Phantom images must be obtained and submitted for review using the phantom that has been approved by the ACR Committee on Nuclear Medicine Accreditation and may be purchased from Data Spectrum (phantom order forms are available in our Testing Overview: Nuclear Medicine and PET article).
The PET phantom uses the base of the Jaszczak Deluxe Flangeless ECT phantom with the spheres removed (as described below) and a PET faceplate. The ACR-approved phantom is a cylinder with an internal radius of 10.8 cm. The faceplate has fillable thin-walled cylinders (8, 12, 16, and 25 mm in diameter), two additional 25-mm cylinders, one for air and one for “cold” water, and a Teflon cylinder (the PET phantom faceplate design is being used by the ACR with the permission of Peter D. Esser, Ph.D., Columbia University; the intellectual property rights belong to Dr. Esser and uses other than through the ACR require his permission). The lower portion of the cylinder contains six sets of acrylic rods arranged in a pie-shaped pattern with the following diameters: 4.8, 6.4, 7.9, 9.5, 11.1, and 12.7 mm. In addition, for the SPECT/PET version of the phantom, the upper section contains six solid spheres with the following diameters: 9.5, 12.7, 15.9, 19.1, 25.4, and 31.8 mm. The spheres must be removed for PET studies. RODS MUST REMAIN.
PET data must be collected and processed according to the instructions provided in the testing package. The acquisition and processing must be essentially the same as those used for clinical whole-body scans. Despite the use of a specific protocol, it is understood that there may still be some differences even if the data are collected on the same type and model PET unit.
The phantom was chosen for evaluating PET tomographic systems because it is relatively easy to fill and set up for a PET study and can be used to measure tomographic uniformity, spatial resolution, and the detectability of “hot” lesions. The variety of resolution and “hot” components enables the reviewers to see relatively subtle differences in system performance.
Acquire the best possible images on your system with the same protocol as a routine clinical whole-body scan. All settings must be documented. Reconstruct the entire phantom as you would for clinical studies.
Site scanning data forms (available as attachments in our Clinical Image Testing: PET article) should be completed for each PET system that is undergoing accreditation. In addition, for each PET system, the applicant is required to submit a list with the frequency of all PET-related quality control (QC) procedures, including yearly, quarterly, monthly, weekly and daily tests (see the PET Quality Control Summary Form available in our Quality Control: PET article).
The ACR requires semiannual testing and strongly recommends quarterly testing of each PET system with an appropriate ACR-approved PET phantom such as described here, in addition to other tests recommended by the vendor.
Preparation of Phantom
Please read all instructions before preparing the phantom. Confirm that all calibrations and QC procedures are current.
One scan will be acquired with the ACR-approved PET phantom. The phantom scan starts 1 hour after Dose A is measured. During the 1-hour preparation time the other doses are measured, vials are filled, background added to the phantom, and phantom positioned in the gantry.
1 ACR-approved PET phantom
1 1000 ml bag or bottle of distilled water or saline solution
2 tuberculin syringes (for measuring Doses A & B)
3 large syringes (60 ml)
Large-bore needles (18 gauge)
Dose: FDG or F-18 are acceptable (Most vendors provide F-18 for calibrations/tests of scanners at a significantly lower price than FDG)
Clock or timer
Phantom dilution worksheet (attached below)
The Table of Dilutions to produce the 2.5 concentration ratio (2.5:1 ratio may represent a lesion in the liver) is presented below. From the left column on the table, select the administered FDG whole-body dose for your site. The activities that are used for the initial Dose A and for the phantom itself, Dose B, are calculated from the F-18 activity normally used by the facility for whole body scans. If the activity is between the values, you must use the one with the higher level. For example, if your facility uses a 5 mCi dose for the whole body scan, you must select the 6 mCi row from the Table.
The corresponding phantom Doses A and B are along the same row as the Patient dose. The second 25 mm vial must be filled with water and the third left empty (“air”).
The spreadsheet indicates the activity that must be used for filling the phantom (this will also be referred to as the “background”) and the “hot” cylinders (“lesions”). Care must be taken to ensure that the solutions in the background and 1,000 ml bag (or bottle) are thoroughly mixed.
Be sure to adjust the "zero" and "background" settings on your dose calibrator. Follow the directions below to measure (± 10%) the doses and activate the PET phantom. Please record all information on the Phantom Dilution Worksheet (attached below).
Phantom Dose Chart
Dose A (mCi)
Dose B (mCi)
Directions for Activating Phantom and Vials
Protocol Summary for the Two Required Doses:
Data Acquisition and Processing
If the phantom does not have a flange on the top, place the phantom on its side at the end of the imaging table. Carefully align the phantom parallel to the axis of the table (left to right). Use a bubble level to position the phantom in the horizontal plane. A folded 3 x 5 card positioned under the end of the phantom can be used to make it level. If a metal plate is present, move the phantom to a position where the plate does not attenuate the photons.
If the phantom has a flange at the top, it should be placed on the table with its flange hanging over the edge. Carefully align the phantom so it is parallel to the axis of the table. If the imaging table has a metal plate at the end, the phantom should be moved to a position where the plate does not attenuate the photons. Material must be placed under the bottom of the phantom, to make it level. To avoid excessive attenuation, the material should only be under the bottom (rod side) near the end of the phantom, not the entire length of the phantom. If the table is continuous, material must also be used to level the phantom.
Use your facility’s whole-body protocol (zoom =1) with the same settings that are used for routine clinical studies.
Reconstruct the entire phantom with the same protocol used for whole body scans including pre- and post-reconstruction filters. Generate 1 cm thick transaxial slices for analysis (if unit is only being accredited for brain or cardiac, use the appropriate protocol for reconstruction). All acquisition and reconstruction parameters should be recorded on the Acquisition and Reconstructions Parameters form attached below.
All images must be corrected for attenuation with the same protocol applied to patient data. Record the parameters on the Acquisition and Reconstruction Parameters form attached below.
Please see the SUV Analysis Worksheet attached below.
ROI Analysis of 1 cm Transaxial Slice from PET Phantom
Regions-of-interest selection: use the minimum, maximum and mean SUV statistics from these regions for the analysis section. See the Phantom Dilution Worksheet (attached below) for SUV parameter instructions.
A. Select the “best” 1 cm slice showing “hot” cylinders (A, B, C & D). Example:
B. Draw a background region (ROI) in the center of the slice as shown here (diameter = 6 to 7 cm). Small variations in size or location of this ROI are not important. Next draw an ROI just inside the largest hot cylinder found in the slice (the ROI is shown in white over the 25 mm cylinder).
C. Place copies of the smaller ROI (as shown in B) over the other visible objects in the phantom slice as shown here. The ROIs should be inside the Teflon, water, and air regions. All ROIs should be 25 mm in diameter. Note that all four of the hot cylinders may not be observed; only the visible cylinders require ROIs. Make a screen capture of the final ROIs with SUV values.
Images for Submission
Transaxial Slices for Phantom Scan: Prepare images that show all of the transaxial slices (1 cm thick) of the phantom. This should include the rod portion of the phantom. Submitted images must be in DICOM format. (DICOM screen capture is not allowed).
Use linear mapping of the display with the lower threshold set at zero and the upper threshold set to the maximum count (or whatever is satisfactory to produce a good gray scale). When there is linear mapping in an image, an ROI with twice the number of counts will have twice the intensity. Label images appropriately.
ROI Images from Phantom Scan: Prepare an image that shows the “best” 1 cm slice of the hot cylinders from the phantom. Scan with the final ROIs image as described above. The ROI images should display the SUV measurements (mean, max, min), or a table included showing the SUV measurements. ROI image(s) with SUV measurements may be in DICOM format or screen capture (jpg, bmp, tif, etc.). See image example below. For more image examples, please refer to the NM/PET Phantom Image Atlas available in our Testing Overview: NM/PET article.
Evaluation of the Submitted Images
Uniformity and noise are evaluated qualitatively by inspection of reconstructed tomographic sections. Optimal density ranges should be comparable to those used for clinical images. Spatial resolution is judged by identifying the smallest “cold” rods in the ACR-approved phantom and lesion detectability is determined from the “hot” cylinders using the region-of-interest protocol above. The same protocol is used for the “cold” cylinders that demonstrate the effectiveness of the attenuation and scatter corrections.
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