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What do the -30 to +60mm markings mean in this MRI scan image?
They are marking distance from a reference plane.
In the images you provided, you are looking at horizontal slices through a brain. The legends are indicating that each plane has that vertical distance from a reference point (if the subject were standing); the positive numbers are dorsal to that reference and the negative numbers are ventral.
A common reference point for MRI images (to define as [0,0,0]) is the midpoint of a line through the pre-auricular point, though ultimately it is an arbitrary distinction.
If the actual reference point is important to you, you will need to verify the reference coordinate system used in the study you are looking at. It's also possible you are looking at coordinates transformed to some reference brain rather than real-life coordinates for that particular subject, but again, whether that matters or not depends on why you care. If you are doing research across subjects, you probably want to know reference coordinates; if you are doing brain surgery on a particular patient you want real-life coordinates.
What does +60mm mean in MRI scans? - BiologyPeople have been killed in the MRI by metal projectiles like oxygen tanks, wheelchair parts and other magnetic objects that came into range. (Photo credit: Liz West, Flickr)
Katy Peters needed to get an MRI for a radical hysterectomy surgery she had coming up. Her doctor told her that should would need to remove her nipple jewelry beforehand for safety (She had a barbell in each nipple). After talking with her piercer, she decided to sign the waivers and go ahead with the MRI while her jewelry was still in.
Since MRI stands for Magnetic Resonance Imaging, and the MRI unit is a giant super-powered magnet, you might imagine that her jewelry came out like Magneto showed up and went to town on her nipples.
The most common fear someone has when approaching the MRI with piercings is having the piercings magnetically removed in a painful way, but a far lesser known and much more common issue is called thermal heating. Like tin foil in a microwave, metal can resonate with the waves in the MRI and get hot. Like painfully so. According to this 2012 study, thermal heating is responsible for 70% of MRI injuries.
So when your doctor is a little iffy about you leaving your jewelry in, it’s because of the potential for injury involved.
Or as one MRI technician told me during a (cough) heated discussion we had: “How am I supposed to know what your jewelry is made of? How do you know what it’s made of? Did you make it?”
The other issue that can come up is what are called artifacts. Artifacts are when something makes the MRI results harder to read. Metals of any kind can make the magnetic field scatter a bit around them and this results in a weird spot. Doctors can’t see around this spot very well because of the interference.
Except Katy’s barbells stayed put and everything was fine.
This article is about why, and about how you, should you need an MRI, can be similarly blessed by the non-ferromagnetic fairy
An artifact blanks out part of an MRI. (Photo credit: kc7fys, Flickr)
and keep your jewelry right where it belongs. We’ll also cover some concerns that your doctor might have, what the risks are, and all that jazz.
First, let’s talk about why Katy’s nipple barbells stayed put.
She went and talked to her piercer about the MRI and was given this advice:
“The barbells were surgical-grade,” she says, “and would not need to be removed. They were made of the same material that bone pins, artificial joints, and surgical screws are made from (which obviously cannot be removed before an MRI) so the removal notice from the hospital was precautionary, given that many folks are unaware what type of metal they have in their body.”
The APP, in their FAQ on jewelry in the MRI concur, as does this handy article by a surgeon that accompanies it.
316L stainless steel. This version of stainless is actually used in some heart surgeries for stents. It’s been shown to be safe in the MRI during lab tests. However, this kind of stainless is most likely to cause artifacts in the MRI readings, making your results harder to read if the jewelry is right near what the doctors are trying to look at.
316LVM implant grade stainless. ASTM-138 compliant steel. This kind of stainless is used in bone pins and other implants. Studies done on this material using surgical staples made of the same steel produced neither heat, nor movement when put in the MRI. In other words, you’re good to go.
What’s the difference between 316L and 316LVM, you ask? As far as the MRI is concerned, they’re likely the same, i.e. fine, but in case you were wondering: The L stands for Low, as in Low Carbon content, which reduces tarnishing from contact with stuff like, well, you. The VM stands for Vacuum Molded, which means it was molded in a special vacuum chamber which seriously reduces contaminants. That’s why 316LVM is the gold standard for steel implants.
But the takeaway is that neither of these steel grades should cause any issue with the MRI except for artifacts.
Grade 5 titanium. This grade of titanium is commonly used in dental implants and those implants are deemed safe for the MRI. For added piece of mind, there’s never been an issue with any kind of titanium and the MRI that I could find. Ever. Titanium isn’t ferromagnetic, and so shouldn’t cause any issues at all except for a tiny amount of artifacts on the MRI results. It’s way better than stainless, but there’s still some interference, so if your piercings are right on top of whatever the doc is trying to see (And we’re talking millimeters) then you might have a problem.
Implant grade titanium. ASTM F-136 compliant titanium. This stuff is made out of material that’s been tested and retested in MRIs. You are golden.
Another MRI (Photo credit: Image Editor, Flickr)
Katy Peters, when she had her MRI done, kept her nipple bars in just fine and experienced no troubles because they were implant grade material.
But research done using lower grades of steel has found that comparable sized materials (Like steel shrapnel or shotgun pellets made of steel rather than lead) showed very little heating, but enough movement at high power levels to cause discomfort.
In other words, no matter what you’re wearing you probably won’t have to worry about the Magneto effect. But thermal heating might still cause an issue.
As a last bit of encouragement, almost all MRI labs have ferromagnetic metal detector wands that they use to scan people. Lots of people have gotten a little metal under their skin from welding or industrial work, so it’s pretty common to have to scan people if there’s a risk.
Ask them to give your jewelry a go with the wand. If the wand doesn’t beep, you’re probably good to go.
And a final note from the MRI technician that I argued with about this subject:
“Don’t they make plastic retainers you can put in your piercings?”Here's another sweet MRI pic for all the MRI lovers out there. (Image Credit: Jan Ainali, Wikimedia)
After posting my original blog, we got a lot of feedback from Facebook (Shoutout to Facebook users Liz, Larissa, and Megan for their great questions). I decided that a follow-up would be good, since there’s not a lot of information out there on some of these questions.
In a surprising turn, Liz mentioned having images in an MRI spoiled by her silicone eyelets. Silicone, being non-metallic, is totally safe to wear in an MRI, but it can cause significant artifacts. Other users have reported that similar things happen during CT scans and X-rays. How close your jewelry is to the area they are trying to scan is obviously a factor.
I double confirmed this with medical professionals and a review of studies done on silicone in the MRI. Given its use in medical procedures, reducing silicone artifacts is a big deal. It’s particularly a problem with burst breast implants, where an MRI would be ideal for showing the extent of the damage, but the artifacts that the silicone causes in the imagery are an issue.
Since MRIs are expensive, you don’t want to have something in place that will skew results and force you to have a second one done.
How bad are the artifacts?
The appearance of “snow storm” artifacts are actually used to diagnose a burst implant or migration of silicone injection fluid. On an MRI, they look like fuzzy white dots or lines, and they’re hard to see through. So if what you’re looking for is right behind it, forget it.
Aside: Never get raw silicone injected into your body. It can cause abscesses, infections, and terrible things. There, I said it.
The problem is called “chemical shift”. If you think of an MRI as a microscope getting focused, the big things to get clear are water and fat. When you get these two into focus, everything else is easier to see. When silicone is present, it can cause a kind focus error, where the water and fat are harder to see clearly.
When MRI folks are working around something like a breast implant, they use special techniques to try and clarify the image. They basically say, “All this stuff is silicone, not fat or water, don’t be confused.” And the MRI focuses accordingly. Without this correction, some lines on your MRI might appear thicker than they should.
In other words, if you’re wearing silicone you might want to think about removing it for the MRI.
Larissa wanted to know about organic jewelry and whether they might cause artifacts. You might think that information would be limited for wood, stone and glass, but it actually isn’t. Thanks to the magic of foreign bodies, aka splinters and such, the effects that these materials have on MRIs is readily known.
Glass is radiopaque, meaning it shows up really solidly on radiographic scans like X-rays and CT scans (Which are really an X-ray variant).
This is an image from an MRI. Because pictures are nice. (Image Credit: RSatUSZ, Wikimedia)
So if you’re wearing glass and going in for this kind of thing, there’ll be a big white spot where the glass is. Great if you have a glass splinter, bad if your doctor is looking for something behind your plugs. But that’s only a problem for something super localized, like right behind whatever glass you’re wearing.
This study and several others that I found tested the ability of different technicians to find foreign bodies imbedded in a sheep’s skull, and include materials like glass, stone, plastic and wood.
In all of the studies I found, I wasn’t able to identify any artifacts caused by these materials. In fact, for finding foreign bodies, the CT scan was actually king. Wood, glass and plastic were all nearly invisible to the MRI, while stone could be seen for reasonably large pieces (Greater than 2mm). I also confirmed with a doctor that none of these materials will create notable artifacts on an MRI.
So glass and wood shouldn’t cause an issue with your scan. Stone is a bit iffier, because remember that stone is not necessarily pure. It can contain iron, silver, and all kinds of trace metals running in veins through the rock. In my previous blog post on the MRI, I mentioned that patients received severe burns from silver filaments in their clothing (This is why you wear a hospital gown into the MRI today). So tiny bits of metals in your stone jewelry could theoretically heat up.
Glass jewelry can also have additives, so if your glass has sparkly things inside, you might want to take it out, just in case.
Megan had probably the most difficult question to find an answer to: How does Niobium fare in the MRI?
While titanium and surgical stainless steel have had rigorous testing and some anecdotal support for their safety in the MRI, niobium does not have much info on how it performs during medical testing. In studies done on Cochlear implants containing niobium rings, the rings were found to exhibit heating of less than .1 degree Celsius, or about .18 degrees Fahrenheit, so not a notable amount of heating. The rings also exhibited zero movement in the MRI.
Interestingly, niobium is used in some implants, most notably some newly designed stents that are between 75-97% niobium. Why did they choose to work with niobium? Because it reduces artifacts in the MRI and because it’s very non-allergenic. Having said that, I wasn't able to find a source who could say that niobium jewelry is safe to wear in the MRI. So the jury is still out on that last one.
How to Determine Which Earpad or Cushion to Order
The best way to find out which of our foam earpads and cushions will fit your headphones would be to make a measurement of your earpiece. When making your measurements, please keep in mind that it is best to measure the physical size of your headphone’s earpiece, not your old earpads or cushions. We have geared all our recommendations on the earpiece size.
There are literally thousands of different makes and models of headphones and headsets. Customers will frequently contact us and ask what cushions are required for their specific headphones. Most of the time we have absolutely no idea, because the headphone manufacturers don’t supply the required details about their product models, sizes and shapes. Each year, new headphones are released with new features that they hope will encourage new buyers. None of the manufacturers provide any details of their replacement parts because they want to make it easier to buy a whole new headphone, rather than worry about supplying replacement parts.
We have started a database showing many of the models of headphones and the known earpads that fit, based on customer feedback. If you tell us which earpads or cushions wound up fitting on your headphone, we well will be happy to post the information online showing which earpads and cushions fit particular models of headphones. Hopefully this database will grow and make it a little easier for customers to find their appropriate earpad or cushion. You will find the database online at the following URL:
HIL53 Cushions Installed onto Logitech Premium Notebook Headset
We do know from experience that many people have long sought out replacement cushions for the Logitech Premium Notebook Headphones, including the Logitech Model A-0445A or Logitech H555 headsets. Our 50mm size foam earpads and leatherette cushions will be perfect for those headsets (shown in the picture on the right). For most others, you will have to make measurements.
We suggest that you take the time to measure your headphone using a ruler. Most rulers have both the inch and metric sizes, as you can see from the ruler shown here.
Many people are perplexed when they have to compare inches and millimeters, but it is really quite simple. As you can see, we did a measurement with the ruler here, and it shows a size of 1 11/16 is the equivalent to 40mm.
Fitting round cushions to oval-shaped or egg-shaped earpieces
Some earpieces are round and others are oval shaped. Our replacement cushions and earpads all start out round. The round ones can stretch to fit onto oval shaped headphone earpieces.
As they stretch in length, they will reduce some in width. We just need to know the proper variation for your headphone so we can determine what circular size will fit on your oval headphones.
In order to determine the proper size replacement earpad or cushion for your oval shaped headphone, you will need to know the average size of the earpiece.
As it stretches to adjust in length, it will correspondingly get smaller in the width.
How to average the width and length of an oval-shaped earpiece
- Measure the length
- Measure the width
- Add the length and width
- Divide by 2 to get the Average
- Convert inches to millimeters
- Match the closest earpad Size
This example shown is an earpiece that is 3 ¼” long by 2 ¼” wide. That is same as 3.25 inches x 2.25 inches.
(length + width) ÷ 2 = average size
So the average would be 2.75 inches. 2.75 inches is the equivalent of 70mm.
How to determine the circumference and diameter
Alternatively, for oval- or egg-shaped earpieces you might find it better to first determine the circumference of your earpiece in either inches or millimeters.
You can use a string, dental floss or just cut a thin strip of paper. Tightly wrap this around the outer edge of the earpiece. Once you know the distance around the earpiece, write down that value as your circumference. If your value is something like 3 ¼ inches, you will want to convert that to decimal format, such as 3.75 inches. Then, divide the circumference by 3.14 (pi) and that will give you the earpiece diameter. Once you have the earpiece diameter, compare that with the tables showing the foam and leatherette replacement earpads and cushions to see what range of sizes point to the appropriate replacement item.
We offer various sizes of foam earpads and leatherette style cushions. The foam earpads can stretch a bit more than the leatherette cushions. So if your measurement is very close to the top end of the size range, you probably won't have any problem stretching the foam earpads a little more. If you are just near the top end of a range of sizes for the leatherette cushions, it will be better to move up to the next size cushion so you won't have to struggle to get the cushion onto your headphone earpiece.
Don't assume that a 60mm measurement will mean that you need the 60mm earpad or cushion. You will need to look up the earpad or cushion that is going to fit, based on the range of sizes in the tables. If you look at the table of foam earpads, for example, you will see that a 78mm foam earpad or 70mm leatherette cushion would be the best one to fit onto a 64mm earpiece.
How to convert inches to millimeters
If you want to convert inches to millimeters, you might find it easy to get help from Google. If you do a search and enter in the phrase “2.75 inches in mm” and hit return. You will get something like this:
Measuring circle-shaped headphone earpieces
Measuring circular headphone earpieces is fairly easy. You just remove the existing foam or leatherette style cushion from the headphone. Measure the diameter of the earpiece. The diameter is the distance from the left edge to the right edge.
Don’t worry about the hole size in the center of the cushion because that is going to stretch and conform to the earpiece. You only want to know the outside “edge-to-edge” diameter of the earpiece.
That will enable you to select the proper earpad or cushion for your headphone or headset.
Normally the material is not glued in place. It is only stretched over the outer edges. In some cases, the cushion will actually go around the outer edges and fit into a thin groove type opening around the face of the headphone earpiece.
Let's say that you have a circular shaped earpiece. You will want to measure across the earpiece from edge to edge. Once you know the diameter, you can easily look to see which earpads or cushions are available.
Replacement of square-shaped foam earpads
Removing square earpad from headphone earpiece
There are some very popular headphones that have square-shaped foam earpads. Our square-shaped foam earpad is typically compatible with them all, because they all seem to have the same style of earpiece. Therefore you will find that our SQ50 square shaped foam earpad will generally fit all those headphones.
If you were to look at the outside of the foam pad, it would certainly appear to be square shaped, however when you look at the opposite side, you will see that the inside opening is usually circular. These earpads actually fit around an earpiece that is usually round or it may be square with rounded edges. The earpiece is typically about 50mm in diameter.
The above picture shows how you would remove the old square shaped earpad from the headphone earpiece.
Square earpad on headphone
Square-shaped foam earpads have a 50mm circular opening
These square shaped foam earpads are found on many Bang and Olefson headphones, such as the B&O Play. These are also found on many of the following headphones:
- Subjekt Pulse Bluetooth Wireless Headphones
- Jaybird Sportsband Wireless Bluetooth Headphones
- GOgroove AirBand Bluetooth Stereo Headphones
How to remove the old earpad
Most earpads and cushions are only held in place by pressure. Usually, you can remove the foam by just pulling it off from the outside edges of the Earpiece. In most instances, you can stretch it around the outer edges to put it right back on again.
If the material is crumbling and falling apart, you may not be able to get it back on the headphone. This is not all that uncommon.
Why old headphone cushions fall apart
Some people want to know why the foam crumbles and turns to dust. Your original foam earpads and Leatherette Cushions were made of a low-grade type of plastic that contains petroleum distillates. As the material ages, the petroleum dries up and the plastic actually breaks into little bits and pieces.
Our replacement ear cushions and earpads will hold up for a much longer period of time, because they are made from higher-grade materials. Unfortunately, the headphone manufacturers planned the obsolescence of the headphones, and hoped that they would only last 2-years at the most. That way they could count on your going out to buy the newest model when your old one began to wear out.
Upgrading headphones by replacing foam earpads with leatherette
Many individuals prefer to order the leatherette style headphone cushions because they feel that the cushion material is softer against their ears. This is all a personal decision that you make on your own.
Many people may find that their older headphones were just fine the way they were. Some may actually choose to upgrade them by installing the leatherette cushions.
Keep in mind that the leatherette cushions are actually a bit thicker, so if your headphones must fit into a charging stand, then the cushion thickness might become a problem.
Available sizes of foam earpads and leatherette cushions
At the present time, we offer the following foam earpads and leatherette Cushions:
|Size||Foam earpad||Leatherette cushion|
|50mm round earpiece - square outside||SQ50|
|80mm teardrop shape||80MM||80LEA|
Replacement earpads & cushions for teardrop-shaped headphones
The 80mm size teardrop-shaped earpads and cushions most frequently fit onto the wireless infrared headphones. Many of these headphones are frequently used on with many vehicle entertainment systems, DVD players and home TV stereo systems.
So if you are looking for an egg-shaped or teardrop-shaped earpad or cushion for an infrared wireless headphone, you may find that the 80mm earpads and cushions are ideally suited for your headphone. The names may be different, however these headphones are all roughly identical in terms of the earpads and cushions. Many of these headphones are branded under the following names:
Many of the vehicle entertainment system headphones look similar to the models above. These types of infrared wireless headphone are frequently used with many of the following vehicle and airplane entertainment systems:
Foam earpads and corresponding earpiece dimensions
|Foam earpad||Part No.||Metric||Decimal Inches||Inches Using Ruler|
|40mm foam earpad||E-20 and E-20-4||24mm - 35mm||0.945 - 1.38 in||15/16 - 1 3/8 in|
|50mm foam earpad||F-30 and F-30-4||35mm - 44mm||1.38 - 1.73 in||1 3/8 - 1 3/4 in|
|Square foam earpad||SQ50||35mm - 44mm||1.38 - 1.73 in||1 3/8 - 1 3/4 in|
|60mm foam earpad||D-60 and T-60||44.5mm - 56mm||1.75 - 2.20 in||1 3/4 - 2 3/16 in|
|70mm foam earpad||L-70 and L-70-4||55mm - 63mm||2.19 - 2.50 in||2 3/16 - 2 1/2 in|
|78mm circular foam||FEP78||58mm - 70mm||2.28 - 2.78 in||2 9/32 - 2 13/16 in|
|80mm teardrop shape||80MM||80mm - 87.3mm||3.19 in - 3.44 in||3 3/16 - 3 7/16 in|
|80mm teardrop shape||80mm||Typically 65mm wide by 80mm tall||2.5 - 2.75 wide x 3.25 - 3.88 tall||2 1/2 - 2 3/4 wide x 3 1/4 - 3 7/8 inches tall|
Leatherette earpads and corresponding earpiece dimensions
DETECTING RISK ITEMS THAT OTHER SYSTEMS MISS
Despite careful, guideline compliant screening procedures, small ferrous objects inadvertently concealed on a patient, visitor or staff member may present a significant risk within your MRI facility.
Ferroguard Screener by Metrasens is the most sensitive ferromagnetic detection system (FMDS) for MRI safety available providing whole body screening with superior detection.
Detection performance comparison – smaller risk items
DETECT THE RISKS OTHER SYSTEMS MISS
Independent testing-laboratory study 8 comparing the performance of Ferroguard Screener in detecting smaller, commonly encountered risk items, against the performance of the other most frequently seen whole-body FMDS.
Only Ferroguard Screener uses Fluxgate sensors, making it the most sensitive FMDS available (minimum detectable magnetic signal, 80 pTesla, 0.8 μGauss). Despite its compact design, it’s super-sensitive to smaller risk-items all the way from the top-of-the-head to the tip-of-the-toes of the tallest patient.
DEMONSTRATED IMPLANT DETECTION EFFICACY
Reported detection of implanted cardiac pacemakers in 75 patients 1 :
– 99.6% Sensitivity
– 100% Specificity
Similar detection efficacy demonstrated for a wide range of implanted ferromagnetic items 2-5
INCREASING THROUGHPUT AND EFFICIENCY
Published studies show 5% of patients still have remaining, unknown, ferromagnetic risk items following diligent conventional screening and gowning 6,7 . Adopting Ferroguard Screener as an additional, final step in your patient screening process can reduce artifacts and time-wasting restarts.
FERROGUARD SCREENER AT A GLANCE
A true FMDS
“The use of ferromagnetic detection systems (FMDS) is recommended…” by the ACR 9 , “…use of conventional metal detectors…that do not differentiate between ferrous and nonferromagnetic materials is not recommended”.
Faster & more reliable
Whole-body screening in seconds. Far quicker and more consistent than with any hand-wand.
Preferred by patients
A less intrusive, more comfortable screening experience
Simple to adopt
Take the pressure off your staff and add objectivity to your screening
Accessible for every budget
A must-have addition to your MRI safety procedures.
Completely safe to use on all patients, including those with implants
The quality you expect
The only FMDS designed under ISO9001 international quality standards
View technical specification
- Ferroguard Screener is to be operated indoors only (Pollution Degree 2)
- It can be operated at any altitude up to 2000m
- Ambient temperature 41 o F – 104 o F (5 o C – 40 o C), humidity 20% to 90% (non-condensing)
- Permitted voltage range 100 V AC- 240V AC, 50 Hz-60Hz
- Temporary overvoltage must not exceed 264V
- Equipment will withstand transient over voltages in accordance with category 2 of IEC 60364-4-443
|Sensor Unit||12lbs (5.4kg)||54.5” (1380mm)||3.9” (100mm)||2.4” (60mm)|
|Power Supply||0.4lbs (0.2kg)||4.0” (100mm)||1.8” (46mm)||1.5” (28mm)|
|Wall Poster||0.2lbs (0.1kg)||23.5” (595mm)||16.5” (420mm)||n/a|
|Floor Mat||0.3lbs (0.15kg)||n/a||23.6” (600mm)||25.6” (650mm)|
|Shipping Carton||22lbs (10kg)||58.5” (1490mm)||8” (200mm)||5.5” (140mm)|
|Voltage Input||100-240 VAC, 50-60Hz|
Note: The power adaptor and any associated cords supplied with your Ferroguard Screener must not be replaced, and must be examined and supplied only by Metrasens.
IEC61326-1:2005-Electrical equipment for measurement, control and laboratory use- EMC Requirements- Part 1: General Requirements
IEC61010-3-2:2005+A1:2008+A2:2009, IEC61010-3-3:2008- Immunity for residual, commercial and light-industrial environments- EMC
Free Guide to MRI Safety & Ferromagnetic Detection Regulations
With multiple professional and accrediting bodies involved, it can be difficult to keep track of what the various published safety recommendations and guidelines in the US say. Metrasens is pleased to assist by providing this summary of the present status as it relates to the growing adoption of ferromagnetic detection systems (FMDS) for the prevention of MRI projectile incidents.
Ferroguard should not be used to replace current MRI screening procedures. The safety of staff and patients is best served by the combination of conscientious screening protocols, thorough staff training AND installation of a ferromagnetic detection system used in the correct manner.
Macro photography: Understanding magnification
Photography, like any other art, demands both compelling content and expert technique to create a pleasing result. In my previous article, I discussed some of the aesthetic choices involved in creating a successful macro image. Technique, however, is an absolute must it's the artist's tool to convey his artistic vision.
Nature, landscape and wildlife are some of the most technically challenging fields of photography, and macro photography comes with its own unique set of technical considerations. In this article I'll be discussing one of the most important ones magnification.
Some of the greatest challenges in macro photography arise from the simple fact that we shoot from very close distances. Thus the magnification of our subject becomes of primary importance. The magnification ability of a given lens is stated in its specifications but in my experience, few photographers understand the meaning and implications of this designation.
To understand the concept of magnification, it's worth taking a very brief look at how a photographic image is created. Every point in a given scene reflects light rays. The front element of the camera lens 'captures' these rays and then focuses them onto the imaging sensor, producing a projection of the scene at the location of the sensor.
Magnification - or more precisely, the magnification ratio - is simply the relationship between of the size of the (in-focus) subject's projection on the imaging sensor and the subject's size in reality. Perplexed? Here are some examples. Suppose that we're photographing a small child, 1 meter in height. Imagine that the height of the child's projection onto the sensor is 1cm. The magnification ratio is 1cm/100cm, or 1/100. Magnification is typically notated using a colon, so we write it as 1:100, and pronounce it, 'one to one hundred', meaning the child is 100 times larger in real life than its image as projected on the sensor. Similarly, if the subject is a 10cm long lizard, and its projection on the sensor is 2cm long, the magnification ratio is 2cm/10cm or 1:5. The lizard is five times larger in real life than its projection on the sensor.
When your subject(s) fills the frame with no cropping involved, it is easy to determine the magnification ratio from a captured image provided you know the size of your subject and the dimensions of your camera's sensor, which can be found in the specifications section of the user manual.
We've seen in the examples above that sensor size can be used to calculate magnification, but the degree of magnification itself depends on focal length and subject distance exclusively (assuming that the lens is not used with any extenders or magnifying filters). Sensor size does not alter magnification. With a fixed focal length and subject distance, an APS-C sensor, for example would just crop the frame compared to a full-frame sensor, not enlarge it. Magnification is a property of the projection, regardless of the size of sensor (or film format) you are using. With a full frame sensor you'd just make calculations using 35mm as the sensor width instead of 22mm, but the subject would then be proportionally larger, cancelling out the sensor size difference.
Sensor size does have an effect on the image's appearance though, a topic I will address in an upcoming article.
What happens if the subject is the same size in real life as its projection? If we shoot a 1cm fly and its projection on the sensor measures 1cm as well, the magnification is 1:1. The 1:1 ratio has an important meaning for macro enthusiasts. Technically speaking, macro photography means shooting at a magnification ratio of at least 1:1. Therefore, a 'true' macro lens has the ability to produce a magnification ratio of 1:1, or higher.
At this point you may understandably ask, what's so special about a macro lens? Surely one can take any old 50mm f/1.8 lens and just move it closer to your subject until you reach 1:1 magnification. The problem, however, is that a regular lens will not be able to focus at such close distances. A more specific definition of a macro lens, then, is one whose minimal focus distance is short enough to allow photography of a focused subject in 1:1 magnification.
Let me take this opportunity to point out that many lens makers employ a very liberal use of the term, and happily write 'macro' on a variety of zoom and prime lenses that are not capable of 1:1 magnifications. This is a sales tactic, and you can easily find so-called macro lenses that can only produce 1:4 or 1:3 magnification ratios. One can, of course, produce great results with such lenses, and it is often possible to achieve higher magnifications on these lenses with the use of optional accessories. When shopping for a macro lens, however, you'll want to look carefully at the magnification specs most 'true' macro lenses will actually have 'macro 1:1' prominently displayed on the barrel. That removes any ambiguity.
Once you have a macro lens, how do you accurately calculate its level of magnification at an arbitrary focus distance? The easiest way, by far, is to use a ruler, as shown in the examples below.
I should point out that with a regular macro lens, 1:1 magnification is achievable only at the very closest focus distance. Using a longer focus distance necessarily means the magnification will be lower. Indeed, for a fixed focal length, magnification is inversely related to subject distance. This relationship isn't linear, i.e. if I get a 1:4 magnification from a shooting distance of 40 cm, I won't necessarily get a magnification of 1:2 (twice that) from a shooting distance of 20cm. However, getting closer will always result in a larger magnification and vice versa, meaning that for our purposes we can use the terms magnification and proximity somewhat interchangeably.
There are cases (such as the image above) where we wish to shoot at magnifications greater than 1:1. These so-called 'extreme-macro' magnifications are possible using special lenses or other equipment, and I'll discuss how that's done in a future article.
For further reading on macro photography take a look at Erez's previous articles in this series:
Polymer degradation is pH-dependent, rapid, and correlates with changes in relaxivity
The pH dependence of polymer degradation was measured in two ways using GPC: molecular weight change over time, and acetone (degradation byproduct) release at different pH values. Though the acetone release results suggest that the molecular weight change graphs slightly underestimate the time for full degradation, both measures show that the polymer is degraded fully at pH 7.4 in one day, at pH 6.5 in eight hours, and is stable at pH 10.
Previous groups have designed degradable polymer contrast agents 14, 27-32 , but have not shown a direct relationship between changes in the relaxivity during the degradation time. Real-time T1 measurements of our polymer solutions coupled with our GPC degradation showed a direct correlation between the change in relaxivity and the degradation rate. We were excited to observe that at pH 7.4 and pH 6.5, the polymer degrades into fragments which have the same relaxivity. This value (3.8 mM -1 s -1 ) is slightly higher than the relaxivity for Gd-DTPA measured in our system, which was 3.64 ± 0.12 mM -1 s -1 , and slightly lower than that of Gd-DTPA-bisamide (Omniscan) relaxivity in plasma, at 37 ଌ and in a 1.5T field, 4.1 mM -1 s -1 1 . Interestingly, the time required for relaxivity to decrease to its minimal value is shorter for both pH 6.5 (3.7 h) and 7.4 (17h) than the time for the polymer to fully degrade by GPC. We speculate that this results from the similar relaxivity of small oligomers formed earlier in degradation to that of the small molecule. These ‘small fragments’ do not tumble slower than the small molecule contrast agent. Our polymer relaxivity measurements are similar to other polymeric contrast agents 2-5 and peptide-based contrast agents 31, 32 .
Degradation-independent effects of pH on relaxivity
While we are confident that the effects of pH on relaxivity over time result from degradation, it should be noted that pH could have additional effects on relaxivity. First, high pH would lead to stronger intermolecular associations, which would lower the degrees of freedom of the system and increase relaxivity 13 . This can be seen ( Fig. 3 ) when at pH 10, the polymer contrast agent at time 0.25 h appears brighter than at pH 7.4, even though according to Fig. 4 , the relaxivity has decreased by only a percent or two. . Similar to our system, relaxivity values for Gd-DTPA have been shown previously to be pH-dependent 33 . Additionally, because each pH is achieved by combinations of different potassium phosphate buffers, each may have a different viscosity, which could affect relaxivity 33 . However, these factors would not cause changes in relaxivity over time. While the starting relaxivity of our data might not be identical, we do observe a change in relaxivity over time, supporting our hypothesis that degradation decreases relaxivity proportionally to molecular weight.
In vivo contrast and clearance
Our polymer contrast agent shows an enhanced contrast and intensity over time when compared to Magnevist ( Fig. 5 and and6). 6 ). Because both our degradable polymer contrast agent and Magnevist are or become small in size, uptake in the liver should be quite limited 34 ( Fig. 6A ). Furthermore, both contrast agents appear to enhance similar areas in vivo both contrast agents seem to prefer the bloodstream and kidneys versus the liver.
The change in contrast patterns over time suggest that our agent is cleared at a similar rate as Magnevist. With both agents, contrast in the bloodstream decreases quickly and that in the kidneys increases simultaneously, followed by a slower decrease towards the initial value after approximately 4 h. Further, contrast increases over the first hour in the bladder, which is associated with renal filtration 35 . We measured Gd concentration in the blood over time ( Fig. 7 ), which indicated that the contrast agent is removed quite rapidly from the bloodstream. We were not surprised that our polymer contrast agent would be cleared rapidly, but had hoped to observe slower clearance time than that of Magnevist. However, our polymer contrast agent could be improved significantly in this regard (see next section).
Limitations and Improvements
Though our MTT assay shows that the pH-dependent degradable polymer contrast agent negatively affects cell viability at high concentrations, we believe this would not likely translate in vivo. These poor-viability readings could result from the high concentrations of buffer needed to attain high Gd concentrations. Furthermore, in the assay, polymer solutions are incubated with cells for 24 h, significantly longer than a similar concentration would persist in vivo. Our polymer rapidly clears into the bladder, which would reduce not only the overall polymer concentration in the blood over time, but also the time window in which the polymer could enter cells in the body.
One area we could improve our polymer system would be to design different degradation rates. Different imaging applications require different circulation times, so a system with an adjustable clearance rate is advantageous. The degradation rate of this polymer could be slowed by incorporating hydrophobic components similar to the work of Paramonov et al. 36 . Alternatively, changing the distance between the ketal and Gd chelating moiety could also slow degradation.
The pH-dependent degradable polymer contrast agent developed here was intended to be a proof-of-concept model, so we chose a straightforward synthesis rather than developing something applicable immediately for human use. Moreover, we believe our pH-dependent degradable polymer is the first step in development of a clinically-relevant blood pool contrast agent. The most critical improvement the polymer system would need is a longer blood pool retention time. This could be achieved in one of two ways. First, following the example of Mohs and co-workers, incorporating a short PEG chain would increase vascular retention, as they demonstrated for a polymer whose molecular weight was quite similar to ours prior to PEG incorporation 37-39 . Second, generating polymers with a higher molecular weight by changing the synthesis route would show an improvement in not only blood retention time, but increased ionic relaxivity, as Karfeld-Sulzer and co-workers have shown 32 .
The second critical improvement is to replace the metal chelating unit with one that binds Gd more stably to further reduce risk of toxicity. DTPA-bisanhydride reacts with amines to form DTPA-bisamides, which are less stable than other Gd-binding FDA approved ligands 1 their thermodynamic stability constant (log K) is 16.84, versus (log K of 22.46) for Gd-DTPA 40 or over 23, up to 25.3 for DOTA and DOTA-modified chelators 41, 42 . While incorporating a stable chelator such as DOTA would involve a more complicated synthetic route, such an agent would be much more feasible for a practical in vivo contrast agent.
The dental pulp is located in the centre of a tooth, made up of living connective tissue and cells.  It is surrounded by a rigid, hard and dense layer of dentine  which limits the ability of the pulp to tolerate excessive build up of fluid. Normal interstitial fluid pressure in the pulp ranges from 5-20mm Hg, marked increases in pressure in the pulp due to inflammation can go up to 60mm Hg.  The rise in pressure is commonly associated with an inflammatory exudate causing local collapse of the venous part of microcirculation. Tissues get starved of oxygen thus causing venules and lymphatics collapse which may lead to localized necrosis.  A common clinical sign associated with the histopathology will be varying levels of suppuration and purulence. 
Following the spread of local inflammation, chemical mediators such as IL-8, IL-6 and IL-1  are released from necrotic tissues leading to further inflammation and odema, which advances to total necrosis of the pulp. 
Further stages of destruction of pulp necrosis often leads to periapical pathosis, causing bone resorption (visible on radiographs) following bacterial invasion. The apical periodontal ligament (PDL) space widens and becomes continuous with apical radiolucency the lamina dura of the apical area will also be lost.  The periapical lesion will enlarged with time and consequently, the pulp will be diagnosed as necrotic.
The pulp can respond (reversible pulpitis, irreversible pulpitis, partial necrosis, total necrosis) in a variety of ways to irritants. This response depends on the severity and duration of the irritant involved. If the irritant is severe or persists for a sustained amount of time it can cause the odontoblasts to die and cause initiation of an inflammatory response.
The odontoblast cell bodies decrease in number and size before any inflammatory changes occur. The outward flow of tubular fluid can cause the nuclei of odontoblasts to be aspirated into the dentinal tubules. The odontoblasts may also be permanently damaged which causes them to release tissue injury factors which can then influence adjacent odontoblasts and underlying connective tissue. Odontoblasts can undergo vacuolization, a decrease in the number and size of the endoplasmic reticulum, and degeneration of mitochondria. It is unknown by which process (apoptosis or necrosis) the odontoblasts die.
Lymphocytes, plasma cells and macrophages comprise the initial inflammatory infiltrate. In response to bacterial assault and tissue injury non-specific inflammatory mediators are released. These inflammatory mediators include histamine, bradykinin, serotonin, interleukins (IL) and metabolites of arachidonic acid. They can interact with neuropeptides (substance P) and calcitonin gene-related peptide (CGRP) during the inflammatory response. Destruction of the nerve fibres causes neuropeptides to be released into pulp. The neuropeptides can cause an increase vascular permeability and vasodilation. The filtration of serum proteins and fluid from the vessel causes the tissue to become oedematous. The tissue pressure increases as the blood volume and interstitial fluid volume rises. The thin-walled venules are compressed and the resistance to flow in these vessels increases. This is accompanied with a decrease in blood flow causing an aggregation of red blood cells and subsequent increase in blood viscosity. This tissue also becomes ischaemic which suppresses the cellular metabolism in the area of the pulp that is affected. This causes necrosis.  Necrosis is a histological term that means death of the pulp.  It does not occur suddenly unless there has been trauma. The pulp may be partially necrotic for some time. The area of cell death enlarges until the entire pulp is necrotic. Bacteria invade the pulp which causes the root canal system to become infected.  Teeth that have total pulpal necrosis are usually asymptomatic except for those that have inflammation which has progressed to the periradicular tissues.
Pulp necrosis arises due to the cellular death within the pulp chamber – this can occur with or without the involvement of bacteria.  It is the result of various connective tissue disease progressions which occur in stages normal healthy tissue becomes inflamed (i.e. pulpitis) which if left untreated leads to necrosis and infection and finally resulting in loss of pulp tissue (i.e. pulpless canals) 
Dental Caries Edit
The influx of bacteria and growth of a carious lesion (if gross and left untreated) inevitably leads to the centre of the tooth – the pulp chamber. Once this tissue damaging process reaches the pulp it results in irreversible changes – necrosis and pulpal infection.  
Dental Trauma Edit
When a tooth is displaced from its normal position as a result of dental trauma, it can result in pulp necrosis due to the apical blood supply being compromised. This might be due to displacement of the tooth through avulsion or luxation. Furthermore, if the tooth is severely damaged, it could lead to inflammation of the apical periodontal ligament, and subsequently pulp necrosis. 
Dental Treatment Edit
Pulpal necrosis can also occur as a result of dental treatments such as iatrogenic damage due to overzealous crown preparation – this may be due to excessive thermal insult and close proximity to the pulp during tooth preparation – or rapid orthodontic work causing excessive force.
Pulpitis is stated to be one of the stages of disease progression which leads to pulpal necrosis. This inflammation can be reversible or irreversible. Due to the enclosed nature of the pulp chamber - unlike normal inflammation - when inflamed, the increased pressure cannot be displaced to other tissues, resulting in pressure on the nerve of said tooth and tissues adjacent.  In irreversible pulpitis where the inflammation of pulpal tissues are not reversible, pulpal blood supply will become compromised and therefore necrosis of pulpal tissues will occur.
Pulp necrosis may or may not arise with symptoms.
Signs and symptoms of pulpal necrosis include
- Pain 
- Crown discolouration  and/or fistula
- Internal root resorption
- Increased tooth mobility
There are additional signs of pulp necrosis which may be detected during radiographic assessment:-
However, in some cases there may be no radiographic signs. For example, pulp necrosis caused by dental trauma which may only manifest/present itself with time, resulting in clinical changes. 
The pain associated with pulp necrosis is often described as spontaneous.  Hot temperatures are reported to have exacerbating factors, and cold temperatures are said to soothe this pain. In some cases, the pain presents as a long dull ache as this is due to necrosis of the apical nerves being the last part of the pulp to necrose. Therefore the pain is from the apical nerves, which have residual vitality remaining when the majority of the pulp is necrosed due to the supply of blood to the more medial parts of the apical nerve. 
Crown discolouration Edit
In some cases of pulp necrosis there is a yellow, grey or brown crown discolouration. Dark coronal discoloration is believed to be an early sign of pulp degeneration.  Teeth with said discolouration need to be treated with special care and further investigations are required before pulp necrosis can be diagnosed. 
Abscess and/or fistula Edit
Alterations in the gingiva such as fistulas or abscesses and radiographic signs such as periapical lesions and external root resorption are used in some studies to diagnose pulp necrosis however other studies state that these factors alone are not enough to diagnose a necrotic pulp. 
Internal root resorption Edit
Internal root resorption may be an indication of pulpal necrosis though it is not possible to diagnose accurately with radiographic presentation of this alone. This is because the pulp tissue apical to the resorptive lesion will still be vital to allow active resorption to take place, it provides the clastic cells with nutrients via a viable blood supply. 
There are a plethora of ways to diagnose pulp necrosis in a tooth. The diagnosis of pulp necrosis can be based on the following observations: negative vitality, a periapical radiolucency, a grey tooth discoloration and even peri-apical lesions.  This altered translucency in the tooth is due to disruption and cutting off of the apical neurovascular blood supply. 
Thermal Tests Edit
Thermal testing is a common and traditional way used to detect pulp necrosis. These tests can exist in the form of a cold or hot test, which aims to stimulate nerves in the pulp by the flow of dentine liquid at changes in temperature. The liquid flow leads to movement of the odontoblast processes and mechanical stimulation of pulpal nerves. 
The cold test can be done by soaking a cotton pellet into 1,1,1,2 tetrofluoroethane, also known as Endo ice refrigerant spray. The cotton pellet will then be placed onto the middle third of the intact tooth surface. The clinical study done by Gopikrishna indicated the tooth to be diagnosed as having necrotic pulp if subjects felt no sensation after two 15-second applications every two minutes.  It is worthy to note that a control test should be performed on the adjacent tooth to ensure further accuracy of results.
Pulse Oximeter Test Edit
The pulse oximeter test is a more accurate way to test for necrotic pulps as it primarily tests for vascular health of the pulp as compared to its nervous response.  This method involves taking measurements of blood oxygen saturation levels, making it non-invasive and an objective way to record patient response regarding pulpal diagnosis.  In a study conducted in primary and immature permanent teeth, results clearly reflected that pulse oximetry can readily differentiate between vital and non-vital, necrosed teeth.
The pulse oximeter consists of a probe containing 2 light-emitting diodes, one of which transmits red light to measure the absorption of oxygenated haemoglobin, and the other transmitting infrared light, measuring the absorption of deoxygenated haemoglobin. As both oxygenated and deoxygenated haemoglobin absorb different amounts of red and infrared light, relationships between pulsatile changes in blood volume and light absorption values can establish saturation of arterial blood. In addition, using absorption curves for both oxygenated and deoxygenated haemoglobin can determine the oxygen saturation levels.  For the purposes of evaluating pulp vitality, it is imperative that the probes fit the anatomical contours and shape of the measured teeth. 
A study was done to assess the accuracy of pulse oximetry in comparison to thermal and electrical tests. Customized pulse oximeter dental probes were placed on the crown of the tooth, with oxygen saturation values recorded after 30 seconds of monitoring each tooth. The values were taken as a positive response (ie vital pulp) within the range of 75-85% oxygen saturation and a negative response below 75%, indicating pulp necrosis. 
Another critically appraised topic  also suggests that a pulse oximeter is more accurate than cold testing in diagnosing pulp necrosis, however comments raised regarding the validity of the evidence stated that the pulse oximeter adaptors were built by the respective authors causing some degree of bias in the experiments. 
3-Tesla Magnetic Resonance Imaging Edit
MRI scans have been used to detect and evaluate several head and neck regions including the Temporomandibular Joint, salivary glands, floor of the mouth, etc. In the clinical study completed by Alexandre T. Assaf, MRI scans were used to detect pulp vitality after trauma in children. The absence of re-perfusion of the dental pulp suggests the lack of revitalization of the affected teeth and hence necrosis of the pulp. In this study, MRI scans prove to be a promising tool to avoid excessive root treatment on traumatized teeth. However, a major flaw in this study is a small sample size of 7. 
The most basic treatment for teeth with pulpal necrosis is root canal treatment. This involves the use of biologically accepted mechanical and chemical treatment of the root system, followed by the placement of a root filling, allowing healing of the periradicular tissues to occur.
Pulpal regeneration can be considered if the following criteria are met:
- Incomplete root development and incomplete apex closure
- Apexogenesis is not applicable as there is apical closure
Pulpal regeneration involves the removal of the necrotic pulp followed by the placement of medicament into the root canal system until it is non-symptomatic. Apical bleeding is then induced to create a clot at the apex which will be sealed by Mineral Trioxide Aggregate. 
In an immature permanent tooth pulpal necrosis causes the development of the root to stop. This causes the walls of the root to become fragile and thin which can make these teeth more prone to cervical root fracture and ultimately the tooth may be lost. These teeth in the past were treated with the calcium hydroxide apexification technique. A disadvantage of this was that it required multiple visits over a prolonged time and there could be an increased risk of cervical root fracture due to an increase in exposure to calcium hydroxide. The apical barrier technique with mineral trioxide aggregate was then used. The advantage of this technique over apexification was that it shortened the number of appointments and the healing outcomes were better. A disadvantage of both these techniques was that it did not allow the root to mature and so regenerative endodontic procedures (REPs) were utilised. A systematic review conducted by Kahler, et al (2017) showed similar clinical outcomes for teeth treated with REPs versus calcium hydroxide apexification/MTA apical barrier technique. They suggested that it should be considered as a first line treatment option in immature teeth with pulpal necrosis. They did state that a thorough discussion with the patient would be necessary as teeth treated with REP’s can show variable root maturation and adverse outcomes. 
Considerations for ESI on Membrane Proteins
Careful consideration in optimizing the parameters are absolutely necessary when analyzing biological materials in mass spectrometric methods. Two examples of these parameters are the collision voltage and selection of detergent 6 . The collision voltage is that which is applied to molecular ions, accelerating them into the collision cell with an inert gas 5 . Optimization of collision voltage involves selecting a voltage that enables fragment ions to be observed, but also well resolved. This voltage goes hand-in-hand with careful consideration of the buffer/detergent. Ideally, the buffer/detergent needs to be able to efficiently solubilize the protein, and also be easily removed to allow the protein to be properly desolvated (see Figures 3 and 4) 6 . Detergents are used for membrane proteins because of their amphiphilic nature, similar to the membrane proteins themselves 6 . Where these two parameters come together are when the membrane protein-detergent complex transfers into the gas phase: the collision voltage must be high enough to desolvate the membrane protein from the detergent, and the detergent must not strongly solvate the membrane protein 6 . Strong solvating detergents require higher energies which risk destabilizing the protein prior to detection in the mass analyzer.
If the membrane protein is not liberated from the detergent, perhaps due to low collision voltage, the membrane proteins' signals maybe be suppressed by noise from the remaining detergent (see Figure (PageIndex<1>)0b and 10f). Figure (PageIndex<1>)0 below also demonstrates the concepts of selecting proper collision voltage combined with an appropriate detergent.
Bone screws have been used in spinal instrumentation since the 1960s. A pedicle screw is a particular type of bone screw designed for implantation into a vertebral pedicle.
What is the vertebral pedicle?
The pedicle is a dense stem-like structure that projects from the posterior of a vertebra. There are two pedicles per vertebra that connect to other structures (e.g. lamina, vertebral arch). The location of a pedicle is illustrated below.
Polyaxial Pedicle Screws
Today's standard is a polyaxial pedicle screw made of Titanium, which is highly resistant to corrosion and fatigue, and is MRI compatible. The screw is threaded and the head is mobile - it swivels helping to defray vertebral stress. Like other screws, polyaxial screws come in many sizes. Polyaxial pedicle screw length ranges from 30mm to 60mm (up to 2-1/2 inches). The diameter ranges from 5.0mm to 8.5mm (up to 1/4 inch).
These screws are used to correct deformity, and/or treat trauma. Similar to other bone screws, pedicle screws may be used in instrumentation procedures to affix rods and plates to the spine. The screws may also be used to immobilize part of the spine to assist fusion by holding bony structures together.
Although pedicle screws are most often used in the lumbar (lumbosacral) spine, they can be implanted in the thoracic and sacral vertebra. The surgeon uses fluoroscopy or conventional x-ray to determine the depth and angle for screw placement. A receiving channel is drilled and the screw is inserted.
Can I Add An M.2 Card if My PC Doesn’t Have a Slot?
For laptops, the answer is no—the design of modern laptops is so compact that there’s no space for any kind of non-planned expansion. If you use a desktop, you’re in luck. There are plenty of adapters for sale that use the PCIe x4 slot already on your motherboard. However, if your motherboard can’t boot from PCIe, then you won’t be able to set that M.2 drive as your boot drive, which means you won’t benefit from a lot of the speed. So keep that in mind—if you want the full benefits of an M.2 drive, you’ll probably need a motherboard that supports it.Michael Crider
Michael Crider is a veteran technology journalist with a decade of experience. He spent five years writing for Android Police and his work has appeared on Digital Trends and Lifehacker. He’s covered industry events like the Consumer Electronics Show (CES) and Mobile World Congress in person.
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