What can I measure or do with DSC's phantoms?
- Simulate in vivo radiopharmaceutical distribution in an emission computed tomography (ECT) slice (SPECT or PET)
- Evaluation of data acquisition and reconstruction methods for brain ECT studies
- System single-slice volume sensitivity
- System total volume sensitivity
- Effect of regional variations in intrinsic system response using uniform cylindrical portion
- Accuracy of attenuation compensation algorithms
- Variation in spatial resolution within the field of view using the multi-sized rod insert
- Lesion detectability using the multi-sized spheres
- Effect of finite spatial resolution and Compton scattering on image quality
- Image contrast, %-RMS noise and signal-to-noise (SN) measurements
- Line spread measurements in air and in water
How do I know which phantom (or size rods/spheres/etc.) to buy?
For higher resolution, we offer the Deluxe Phantom (Model ECT/DLX/P) and for even higher resolution, is the Ultra Deluxe Phantom (Model ECT/U-DLX/P).
For legacy systems or those with generally poor performance, we offer the Benchmark Phantom (Model ECT/BEN/P). The cold rods in its insert range from 9.5 to 25.4 mm and the 6 spheres are 12.7 to 38 mm
Please note that when you purchase a “QC” phantom of the circular cylinder type, you receive a cylinder with cover plate and the insert of your choice. If you wish to add to your imaging options, you can purchase only the inserts (rods or spheres) and use your existing cylinder.
Note that some of our other phantoms will have a single insert that is available. Please see our Products page see the full line of phantoms and options for each particular one.
The “QC phantom” line is only part of our offerings. Some phantoms are designed for evaluating neurological studies (brain phantom models include 2-D, 2-D multi-compartment and 3-D versions), torso phantoms, elliptical QC phantoms, a NEMA phantom and cardiac phantoms. We also supply a wide array of inserts and accessories, and a series of phantoms and inserts for super-high resolution “small animal” scanners.
So, please look through our catalog to find the phantom that you think best suits your needs. Of course, if you want help deciding or just have questions in general, please contact us.
Why Do I Need a Phantom?
You cannot determine these parameters very easily in a patient, and even if you did, you probably won’t have the same patient back with exactly the same “configuration” month after month when you are performing Quality Control procedures … and you can’t fill arbitrary locations in patients with just any arbitrary amount of radioactivity.
With a phantom, you can:
- have a standardized test procedure
- compare your results from month to month
- compare your results to your other scanners, or to those at other institutions
- decide on clinical protocols for acquisition and processing ahead of time
- practice patient setup and image processing techniques
In what locations should I position spheres in the SPECT or PET QC phantoms?
What kind of lubricant should be used on O-rings and where can I buy it?
One acceptable product for use on O-rings is “Silicone Lubricant” in the catalog at http://www.tryphon.it/catalogo.htm. The catalog description says “Special silicone lubricant with PTFE”, and it is fairly inexpensive.Another acceptable product for use on O-rings is Gunk Plumber’s Silicone Grease. The Gunk part number is GR2V. You can find more information about this product at http://www.gunk.ca/prodsht-en/gr2.pdf (link will open in a new window). We found Gunk Plumber’s Silicone Grease in local hardware stores and the plumbing department of home improvement companies (such as Lowes and Home Depot). It may also be available at plumbing supply companies and auto part dealers.
How do I receive the correct manual?
What is the procedure for placement of the solid spheres?
How do I eliminate air bubbles in the Mini, Micro and Ultra Micro line of phantoms?
How can I accurately simulate bone density in a fillable phantom (or insert)?
What is the density of the fillable lungs in certain body phantoms?
2. Measure Lung volume with Styrofoam beads installed in lung [V(lung)]
3. The fraction F is simply the fractional amount of water that can be used in the presence of the beads and is equal to density of the lungs when it is multiplied by the density of water (1 gm/cm3):F = V(lung)/V(total) gm/cm3To repeat, typically, F is about 0.3 to 0.4, depending on how tightly one packs the Styrofoam beads in to the lungs.
What is the density of the Teflon spine in certain body phantoms?
thick = object thickness in cm
ref = reference counts (no material between detector and radiation source)
obj = object counts (material is between detector and radiation source)
mu = mu value Calculations:
a = obj/ref
b = natural-log (a)
mu = b/thickSuppose that: obj = 80920 counts (through a material) ref = 139890 counts (reference beam) and the material thickness = 3.4 cm, then:80920 / 139890 = 0.5784545 (divide object counts by reference counts)
ln (0.5784545) = -0.54739539 (take natural logarithm)
-0.54739539 / 3.4 cm = -0.16099864 per cm (divide previous step by thickness in cm)
Other notes: “Virgin Teflon” can refer to any of a number of specific chemical compositions such as PTFE, FEP and PFA, among others. The exact compositions are proprietary to DuPont, the manufacturer of Teflon.
What is the atomic number, density and composition of the phantom material?
The systematic name is methyl 2-methyl-2-propenoate. Its molecular formula is H2C=C(CH3)COOCH3.Information about polycarbonate can be found here, which is also a URL at NIST.
What contrast agent should I use for MRI Scans?
Why is my resolution is very poor?
- inappropriate collimator
- camera is unnecessarily far away from phantom
- center of rotation (COR) correction values are not up to date
- phantom moved during scan
- poorly chosen reconstruction filter – too much blurring
- acquisition and/or reconstruction matrix size too coarse
- you may have the detector tilted with respect to the axis of rotation (this is not a possibility on some scanners)
Note: Not having “enough” counts in the reconstructed images does not affect resolution, except to the extent that you don’t have enough information to see what resolution capability is (or would be) there with “enough” counts. You essentially have in this case just a noisy, although possibly high resolution, image.
- Image Problems: I see areas that are hot, where I do not expect to see any hot area. What causes this?First make sure that you are not seeing circular artifacts caused by camera non-uniformity. If you don’t think that is the problem, look at the location of the hot area of interest. If it shows up at the exact center of the phantom, for example, it could be that you are seeing a nylon screw soaking up Tc-99m pertechnetate. The hot area in the accompanying photo below demonstrates an example of this phenomenon.
The hot area at the center of the phantom (red arrow) is actually the Tc-99m pertechnetate that has been absorbed onto the surface of the nylon hold-down screw. The center of the screw does not show any activity – yet – but in time, might eventually show activity to some degree. It has been our experience that this uptake increases over time, and may not appear if you can finish your scan soon enough after adding radioactivity to the phantom.There are several possible fixes for this problem. One way is to use a Lucite ® rod with a cap (user supplied). This will not show uptake of radioactive material onto the rod. A probably better way, which we have had good success with, is to use another radiopharmaceutical, like Tc-99m DTPA. We suspect that this phenomenon has to do with the differences in electrical charge of pertechnetate versus DTPA. Other radiopharmaceuticals might also allow for imaging without having the screw show up.Another avenue of research would be that of pre-soaking the screw with some other (non-radioactive) solution that would saturate whatever binding sites that the Tc-99m would normally stick to. If you find such a solution (pun intended), please let us know about it.
My reconstructed images are very noisy. What can you do about it?
- scan for longer times
- use more radioactivity
- filter more
- add adjacent slices together
- acquire (or process) the images with smaller matrix size (thus increasing the number of counts per pixel)
- consider using “smart” reconstruction programs such as OS-EM or ML-EM instead of filtered backprojection
- I see rings in my reconstructed images.Generally, “ring” or “circular” artifacts (see accompanying image) are caused by less then adequate uniformity of camera response. This means that a uniform source of radioactivity, like a flood source, does not appear uniform in the images (projection data) acquired into the computer. A full discussion of this phenomenon can be found many other places. Usually, the cure for these artifacts is fairly simple. (Note: In the slice shown containing the rods, the cold areas between each sector and at the center of the phantom are the
rods that support the spheres and the hold-down bolt, respectively,
and are not artifacts.)Present day image reconstruction software usually takes care of this problem by “allowing” (translation: “forcing”) the user to acquire uniformity correction images, usually with a high number of counts – 100 million is a typical number. This image is processed to “map” the non-uniformities in the camera response and generate a correction matrix.Please see your camera’s or computer’s User Manual to determine the method of acquiring and applying flood correction images to your scans. Typically, this is necessary as often as every month to as long as every 6 – 12 months, depending on the camera and its stability.
How can I know if I really obtained the concentration (or concentration ratio) that I wanted?
Note: Because well counters are so sensitive, you might have to wait until your unknown sample decays to below a fraction of a uCi to count it to avoid serious dead time losses. Alternatively, you might consider diluting your sample, if that is an option with your particular circumstances. Try also to make sure that you use as close as possible to the same counting geometry – same volume, material, container, placement within the detector or container, etc.
How can I measure out such small amounts of radioactivity and volumes?
((48.1 – 48.0) / 48.0) * 100 = 0.21 % error
For more exacting applications, q.s. the radioactive volume drawn up from the dose vial (0.1 ml) up to 48.0 ml. In other words, add the 0.1 ml of radioactivity to 47.9 ml of water.
Is there some simple way to get desired concentration ratios of two or more radioactive solutions?
– Solution #2 (S2) needs to be 5 times that (50 uCi/ml) in 100 mlMake S1: We see that we need a total of 2000 uCi (10 uCi/ml times 200 ml). If we happen to draw up 2080 uCi, we see that we need 208 ml of non-radioactive water (2080 uCi / 208 ml = 10 uCi/ml. (We have 8 ml of spare solution: 208 ml available minus 200 needed).Make S2: Since S1 was 10 uCi/ml and we want a 5:1 ratio, that means S2 has to be 5 times S1, or 50 uCi/ml. We want S2 to have a total of 100 ml, so we need 50 uCi/ml times 100 ml, for a result of 5000 uCi.So, for making S2, we happen to draw up 5130 uCi. To get our 50 uCi/ml target concentration, we dilute 5130 uCi in 102.6 ml (which is 5130 divided by 50). Mix the 5130 uCi in the 102.6 ml and you are done! Again, the key to making this solution (no pun intended) work out is to draw up slightly more uCi of radioactivity than initially expected. That way, you can much more easily draw up “exact” volumes of water needed – much more easily than drawing up exact numbers of uCi, plus you have extra volume in case you should spill some.
s there some simple way to get a desired concentration of radioactive solution?
Of course, don’t forget to take into account radioactive decay if there is significant delay between drawing up radioactive volumes from your dose vial. Also, don’t forget you might want to take into account the volume of the radioactivity that you draw up when mixing it into your stock solution. If the volume of the radioactivity you draw up is more than a few percent of that of the “cold” water you are going to mix it with, you might wind up with significant errors in concentration.
This method allows you to handle radioactive material once or twice at most, and instead can spend more time accurately gathering the exact volume of non-radioactive water.
Yes, you will have 2 ml of excess volume, which is actually desirable. If you have *exactly* the volume you need and should spill some, then you will have to either make up the volume with non-radioactive water which would change your target concentration (or live with an air bubble), or you would have to make up another batch.
Again, since you are dealing with radioactivity, you want to minimize the amount of time spent handling it.
One more (repeated) reminder: Especially when dealing with small total volumes, do not forget to take into account the volume of radioactivity solution you draw up from the dose vial! It could cause an unintended error in your total volume leading to an error in desired concentration.
For example, if you withdraw 100 uCi from the dose vial in 0.2 ml , and you want a *total* of 1.0 ml, be sure to add your radioactivity to 0.8 ml. Otherwise your concentration will be:
83.3 uCi/ml = 100 uCi / 1.2 ml
100.0 uCi/ml = 100 uCi / 1.0 ml
for an error of about 17%.
The key to making this solution work out correctly is to draw up slightly more uCi of radioactivity than initially expected. Then, you can easily draw up “exact” volumes of water needed – much more easily than drawing up exact numbers of uCi. Additionally, you have extra volume in case you should spill some.
- Determine your desired concentration and desired water volume.
- From that information, calculate the necessary number of uCi.
- Draw up a little more radioactivity than needed.
- Based on the number of uCi, calculate the new volume of water now necessary to obtain your desired concentration.
- When dealing with small volumes (relative to the volumes of radioactivity withdrawn from your dose vial), be sure to take into account the volume you draw up when adding that to your non-radioactive volume of water.
How can I measure the amount of water that I've added to each sphere?
A. Use a TB type syringe, whose total volume is 1 ml or less.
B. Be certain to get all bubbles out of the syringe, including the needle.
C. Before filling the sphere, squirt out 1 or 2 drops of water into a waste receptacle; this helps ensure no air was left in the needle. Write down the volume shown on the side of the syringe.
D. Subtract the post-filling amount of syringe contents from the pre-filling amount to calculate the water volume inserted into the sphere.The other method involves the weighing of the sphere before and after filling, calculating the weight, and converting to volume. The weights will be on the order of grams, and so you will need a fairly sensitive device.
One that works well for this application is the Mettler PE 360 (Mettler-Toledo, Inc., 1900 Polaris Parkway Columbus, OH, 43240, Phone: +1 614 438 4511). This method assumes that a gram of water corresponds to 1 ml of volume. Weigh the sphere before and after filling, and subtract the weights to determine the water weight. Convert grams to ml to get the volume. Example: A sphere weighs 20.0 and 25.1 grams before and after filling, respectively. The weight of the water is 5.1 grams, and thus the volume is 5.1 mls. Note that this assumption may not hold true for solutions of water and other components, like CT contrast media. In this case, you can determine the weight of the solution (put a known number of mls in a container that you have weighed before and after putting the solution in) and then determine ml per gram. Unknown volumes can be determined by calculations based on the weight of the test solution. Example: A 5 ml solution weighs 5.8 grams. So the solution is 1.16 grams/ml. Now if the sample whose volume is unknown has a weight of 2.32 grams, we divide 2.32 by 1.16, for a volume of 2.0 ml. Note that these are just some “made up” example numbers and may not be similar to your solutions.Note that sensitive scales are, well, sensitive. This means that you should use the shields that come with the scales to seal the measuring chamber against air currents that will produce erroneous measurements. Other tips to using (electronic) scales:
A. Allow sufficient time for the instrument to warm up after turning it on. The various components will drift over time until they stabilize, which might take 15-30 minutes or so.
B. Make certain that the scales are on a flat, level surface. “Level” the adjustable feet on the instrument, if it has this type. Some instruments have a built-in bubble level.
C. Some scales have “tare” capability. This means that you can, after allowing the machine to warm up and stabilize, place the empty sphere on the scales and “zero” the reading on the display. After you fill the sphere and weigh it again, you can then read the weight of the water in the sphere directly off the display without having to perform any arithmetic calculations.
D. Avoid making the measurements if the scales are placed in a location that experiences a lot of vibrations on the table-top. These can come from HVAC systems, large passing trucks, nearby construction, etc.
I would like to have the hollow spheres located at a different height than what the standard stems (support rods) provide. How can I do this?
Please see the accompanying figure, in which the lowest sphere is on a modified support stem. You may notice that it appears white, rather than clear like the other two rods. This rod was made from a nylon screw in which the head was removed. In regards to the other two spheres, it shows how you can substitute the stems for one sphere with the stem for another. The way to get customized stem heights is to take nylon or Lucite ® threaded rods (¼ x 20) and cut them to the desired length. The seal you obtain may not be quite as good as that you would get with the standard stems, but the result should be sufficient.
Tips on cutting rods:
- Put a metal nut on the rod before cutting, on the side of the cut that you will keep.
- You can run the nut up to the desired cut location and slice through the rod with a knife-like object heated with a propane torch, or you can use a standard hacksaw, coping saw, Dremel rotary tool or similar tools. A saw blade with finer teeth usually makes for better looking and easier to use cuts.
- Once you have cut the rod, screw the nut off of the rod. This will help shape the threads to the proper shape. A metal file, grinding wheel or similar tool can help shape the cut end(s) to where it will more easily screw into the base plate and/or the neck of the sphere. Another helpful tool is the Xcelite Standard Lead Shear (model 170-M) cutter, or the Super Shear Flushcutter (model 170-D). These are excellent for trimming small, deformed pieces of threaded nylon off the newly formed stem.
- A good alternative to threaded rods is nylon screws or bolts, which are readily available. Cut the head off of the rest of the screw or bolt per the above instructions. One source of nylon screws and bolts is SMALL PARTS, Inc., 13980 N.W. 58th Court, P.O. Box 4650, Miami Lakes, FL 33014-0650, Phone: 1-800-220-4242.
- DSC recommends that you do not use metal rods or screws in place of the supplied stems. Also, never use pliers or other tools to tighten phantom parts. If you have to resort to pliers to unscrew a stem or other phantom part, place a soft cloth or folded paper towel between the part and the pliers to avoid scratching it or leaving indentations. Applying too much pressure will crack the phantom parts and void your warranty. Never put pliers on the spheres – they are almost guaranteed to break, and this breakage is not covered by the general warranty.
How do I care for and clean my phantom?
How do I know what the SPECT resolution of my system should be?
- relatively fine acquisition matrix and pixel size (use the smallest pixel size your system supports if you want to determine “ultimate” resolution) – 2mm or less should be sufficient
- 120 to 180 angles for SPECT scan, over a 360 deg. range
- line source approximately 5 to 10 cm long, containing 2 to 10 milliCuries
- collimator: user selected
- planar image acquired for 1 to 3 minutes; SPECT scan acquired for total of about 3 to 10 minutes; be sure not to allow pixel overflow in planar or SPECT acquisition, and in the reconstruction; adjust time accordingly
- How do I make my own capillary line sources and how do I fill them?You can order bulk amounts of glass capillary tubing from scientific supply houses. One example is Kimble #46485. Tubes should be about 1mm inside diameter for clinical-type scanners..Once you have your tubing, you can cut it to the desired length with a small, metal triangular file. This is a technique that takes only a small amount of practice to become proficient at. Using very light pressure, hold the tube in between your thumb and forefinger and gently press one corner of the file against the tube where you would like to cut it. (Holding the tube in the fingers works better for the author of this FAQ, rather than trying to lay the tube on a hard surface.) Using too little pressure will fail to scratch a mark on the glass, while too much pressure will basically shatter the tube at that mark. So, take care not to cut yourself; We suggest you don protective eyewear.Once you have a scratch mark at the desired location, put the thumb and forefinger of one hand on one side of the scratch mark and close to it, then do the same for the other hand on the other side of the scratch. Have the scratch mark away from you. Gently bend the tube and it should break cleanly, with a nice even edge on each new end of tubing.Filling the tubes also requires requires a small amount of practice, which you can do with non-radioactive water. The tube may be filled using capillary action by tilting one end of the tube and touching it to the surface of a drop of the radiotracer solution. By holding the other end closed, the tube may then be removed from the solution and sealed with a sealer such as “SealEase” or with a putty compound such as “Mortite”. The author normally seals both ends. This way, if the source should break, there is a likelihood of less solution leaking out the unsealed end of tubing.After filling and sealing your line source, you might want to rinse the end touched to the radioactivity and dry the line source. Of course, please take appropriate precautions not to accidentally break the source, as you could cause radioactive contamination of other objects.
How can I measure the resolution of my system?
What kind of water do I use to fill the phantom?
What if the phantom leaks?
What if I break or lose a part of my phantom?
Reminder: Never use metal screws in place of nylon or acrylic (Lucite ® ) screws!
What is the warranty on DSC Phantoms?
Data Spectrum Corporation warrants the product to be free from defects in materials and workmanship, under normal use, for a period of ninety (90) days upon receipt of product(s). If Data Spectrum Corporation receives notice of defects in materials or workmanship during the warranty period, Data Spectrum Corporation will either, at its option, repair or replace product(s) that proves to be defective. With continued responsible and careful use, the product(s) should provide excellent service.Exclusion: The above warranty shall not apply to defects resulting from improper or inadequate use or maintenance by the buyer (or representative thereof), unauthorized modification or misuse, operation outside of the environmental specifications of the product, improper site preparation and maintenance. Data Spectrum Corporation or any authorized representative will not be liable for any expenses incurred outside this warranty. Data Spectrum Corporation does not warrant that the functions contained in the product(s) or manual(s) will meet each individual requirement, or that the operation of the product(s) or manual(s) will be uninterrupted or error free.Warranty Limitations: Data Spectrum Corporation makes no other warranty, either expressed or implied, with respect to this product(s). Some states or provinces do not allow the exclusion of implied warranties, so the above exclusion may not apply. This warranty gives the buyer specific legal rights, and the buyer may also have other rights that vary from state to state.
What should my quality control scan consist of?
- high resolution or general purpose collimator
- 30-60 milliCuries of Tc-99m (SPECT scanners)
- 128×128 acquisition matrix, zoom 2.0 (or the equivalent of about 1.7 mm/pixel)
- 120 angles (“stops”) per camera, with a full 360 deg. rotation of head(s)
- scan for about 30-60 seconds per angle
- reconstruct with desired filter (start with ramp filter), attenuation compensation (either measured w/TCT scan, or assume 0.12 per cm); add anywhere from 10 to 50 slices in the rods section together; add 3 to 4 slices of spheres section together; add 10 to 20 slices of uniform section together
- for multi-camera scanners, reconstruct each head individually and then all heads combined
- inspect for presence of artifacts, resolution, etc.
- compare with previous scans; archive results
We are told that some institutions set up their QC scan to begin as the technologists are leaving work, allowing the scan to take place after normal working hours, and then processing it the next day. You should first determine that the use of this method complies your institution’s regulations and state and federal regulations with regards to unattended scanner operation, and with regards to concerns of possible unauthorized access to radioactive objects.
How often should I perform my quality control procedure?
- installing a new system
- after having “major” retuning or repairs on the scanner
- after new upgrades of software
- “certifying” or training new personnel
How do I reconstruct my scan images?
Quick filter lesson: Filters can be generally thought of as blurring functions, that is, they only allow lower spatial frequencies to be used during the reconstruction process. Thus, they are often called “low-pass” filters. Filters are typically designed with at least one (but sometimes more) user specified parameter known as the cutoff frequency. This value is usually expressed in cycles per cm, but can be in other units. A larger cycles/cm value means that less blurring is taking place. Thus, a filter with a cutoff frequency of 1.6 cycles/cm does less blurring (and looks noisier) than one with a value of 0.5 cycles/cm.
Reconstruct each head individually, and then all heads combined. Perform attenuation compensation with either a measured TCT map or use a value of 0.12 per cm constant value.
Note: The true attenuation coefficient values for water and Lucite ® are approximately 0.15 per cm at Tc-99m energies. Using a value of 0.12 instead of the true value will artificially “compensate” for the extra apparent activity near the center of the cylinder that results from scattered photons. Note that this is an ad hoc method, and that it provides a close enough approximation for many applications. It will result in a relatively flat profile across the transverse images.
Another point to remain aware of is that the reconstruction software of some scanner systems is configured to use units in terms of cycles per pixel instead of cycles per cm. You should determine if your system is this type and make adjustments accordingly. Contact the vendor of that system to obtain values that are appropriate for your uses of the system. It is impossible for us to provide a specific value, since converting from inverse centimeters to inverse pixels would depend on the matrix size and the field of view of the camera.
For the cold rods sections of the QC phantom, you probably will want to add 10, 20 or more slices together to improve rod visibility and reduce noise. For this to be successful, you must position the phantom in the scanner as perfectly aligned with the axis of rotation as is possible. Otherwise, any tilting will mean rod locations in one slice will be slightly shifted in subsequent slices. When you add them, the rods will not “line up” and you will just have blurred images.
For the slices encompassing the spheres, pick the 2 to 4 slices that seem to include the smallest sphere, and then add these images together. In the uniform section of the cylinder (the volume between the spheres and the phantom’s cover plate), add together 10 to 20 or so of these slices.
Note: Depending on your computer’s software and the number of counts in the transverse images, you might have to scale the images down before adding them, so that you don’t have overflowed values in some pixels. Basically, this just means you have to divide the images by some factor like 2 or 5 or 10 before adding them. Typically, most Nuclear Medicine images today are arrays of 2-byte integers (the “pixels”), which means that the pixel can store a value no higher than 32767. (There is at least one system on the market that has 2 byte integers that have a value range from 0 to 65K, but I did say “typically”, above). If a pixel is told to be set to some number greater than 32767, it “overflows”. The value is too high for the integer format declared in the program’s source code, and may (internally in the particular bit pattern of the bytes) appear to be negative or some astronomically high number. It will depend on the “sign” bit and the variable’s declaration in source code.
Do you have any helpful hints and precautions for filling/draining my phantom?
- Wear gloves, lab coat and protective eye-wear when dealing with radioactivity.
- Use time, distance and shielding as much as is practical to reduce radiation doses to personnel.
- Following a well thought out plan of action will avoid wasting time and will help reduce radiation exposure. Ask yourself “Exactly what is it I want to learn from this scan?”. This will help make sure that you will obtain the desired information and it will help reduce the number of repeat scans later on that you will have to perform.
- Have all your materials (tools, phantoms, mixing containers, etc.) ready before beginning your experiment. This will help reduce the amount of time you are exposed to radiation
- Fill the phantom with water that is at or slightly above room temperature (but not hot!). This will help to:
- prevent the potential cracking of the phantom when the water volume increases as water temperature equilibrates with room temperature (if you were to start with cold water). Since the sealing ability of the caps (with O-rings) is very high, increased pressure in the phantom might in rare instances damage the phantom.
- prevent water from spraying out when a cap is removed. While the number of ml’s involved would be very small, we wish to alert you to the potential for contamination.
- create a very slight vacuum as the water cools, which will help insure against leakage if the caps or O-rings are not properly sealed. Normally, leakage would be a rare event with ordinarily encountered temperatures.
How much radioactivity do I put in the phantom?
For other phantoms or other applications, a good starting point is to do a literature search and see what others in the field have done. We suggest to start with a search on Google.
How do I position the phantom?
This will obtain better resolution than having the camera(s) far away from the phantom.You will have to determine how you actually “mount” or suspend the phantom in the scanner opening. Many people lay the phantom on a blanket or similar object on top of their scanner’s patient bed.
Other institutions have made special holders that clamp onto or replace the head holder. Others have used the collimator changing cart as a support, with adapters to actually support the phantom.Once you have decided upon a mounting method, and while monitoring the phantom position on the persistence scope or computer monitor, the angulations and tilts of the phantom can be adjusted prior to the scan.
While still in “persistence” mode, rotate the camera to top, bottom and sides of the phantom. Adjust the phantom position based on these images. Generally, you will look for the edges of the phantom to be parallel, or “square”, with the edges of the P-scope.
How do I fill my phantom?
- First and foremost, decide on what it is that you want to do! Know ahead of time what it is you want to learn from the scan. Decide before the planned scan time what concentration ratios (if applicable), acquisition parameters, scan length, radioactivity levels, etc. that you want to use. If your experiment depends on concentration ratios, measure the volumes of the chambers that you are going to fill.
- Remember: You are dealing with radioactive materials, so you want to minimize the amount of “fiddling around” measuring volumes, deciding on phantom positioning, total amount of radioactivity to use, etc. You might want to re-read the previous guideline in this series.
- If possible, get together the water to fill the phantom with several hours, or even a day, ahead of preparation time. This will allow dissolved air to escape out of the water, leading to fewer bubbles forming during your scan, and will allow it to equilibrate to room temperature.
- Pre-mix the radioactive tracer with water in external containers instead of injecting the radioactivity into an already filled phantom. This is usually always easier and provides a more uniform solution.