REPORT FROM THE IMAGING PRACTICE ACCREDITATION SUBCOMMITTEE Patrick Byrne, MS, Carmel, IN, Tyler Fisher, Costa Mesa, CA

Accreditation of Non-Traditional Nuclear Medicine Systems

For many decades, Nuclear Medicine was limited to large sodium iodide detectors coupled to photomultiplier tubes. In recent years, the field has seen the introduction and development of a variety of non-traditional, specialized imaging systems. Typically, these systems are intended to image individual organs such as the heart and breast. As their focus is limited, they have been able to optimize their capabilities through the use of unique radiation detectors and proprietary reconstruction methods. These systems are not able to function in the same manner as traditional gamma cameras, so many of the tests described in NEMA NU 1-2012 Performance Measurements of Gamma Cameras are not even possible, if relevant at all. Nevertheless, the American College of Radiology Nuclear Medicine Accreditation Program does provide accreditation coverage of these systems.

Non-traditional Nuclear Medicine breast imaging systems include the GE NM750b, the Dilon 6800, and the Gamma Medica LumaGEM. These systems feature small detectors that are capable of planar imaging only. The NM750b and LumaGEM are cadmium zinc telluride (CZT) based and the 6800 utilizes thousands of individual sodium iodide crystals whose scintillation light is detected by an array of position sensitive photomultiplier tubes.

While the ACR NMAP program requirements do not mention breast imaging units, the ACR will accredit them. A facility accrediting one of these systems should contact the ACR for guidance. The physics portion of testing requires the submission of a uniformity image as well as a resolution image. For resolution, the ACR allows the submission of either a four-quadrant bar phantom or a planar image of the ACR SPECT phantom. Generally, due to geometric limitations, imaging of the SPECT phantom is not practical. Therefore, imaging of a four-quadrant bar phantom is the most likely method for resolution evaluation.

Breast imaging systems are generally not capable of performing all the recommended ACR recommended Nuclear Medicine performance tests. However, some of the tests are able to be performed and each system has built-in quality control routines. Many of the manufacturers have developed documents that provide guidance on the tests that can be performed as well as specifications for normal/abnormal operation. Performance of these tests by the qualified medical physicist or an individual under their direction should be conducted annually in place of the tests detailed in the Nuclear Medicine accreditation program requirements.

An even wider array of systems has been developed to image the heart. Some of these systems are traditional gamma cameras, albeit with smaller field of view (FOV) detectors. Systems in this category include the Siemens C.Cam, the Philips CardioMD, and the GE Ventri. All use sodium iodide scintillators coupled to photomultiplier tubes. These systems are able to perform both planar and SPECT imaging and therefore all the annual Nuclear Medicine performance tests can be conducted on them. Due to their limited FOV, the Deluxe ACR SPECT phantom cannot be fully imaged. The ACR recommends the use of the Data Spectrum Small SPECT phantom for limited FOV systems. This phantom has a diameter of 14 centimeters instead of 20.4 centimeters and will completely fit within the FOV while imaging.

Non-traditional cardiac imaging systems use a variety of detectors, collimators, and reconstruction algorithms. The most commonly encountered non-traditional cardiac systems include the Digirad Cardius, the GE Discovery NM530c, and the Spectrum Dynamics D-SPECT. Digirad systems utilize solid state cesium iodide crystals coupled to a silicon photodiode. These systems also use traditional collimators, with parallel-hole being the most common. The Discovery NM530c and D-SPECT are CZT based systems, with integrated, non-removable collimators. These systems are designed to only perform SPECT imaging of the heart and are not able to perform planar imaging at all. Each has a modified daily quality control procedure, whose method and specifications are described by the manufacturer. The ACR Accreditation Program allows either the Small SPECT phantom or the Deluxe SPECT phantom to be used on these systems.The Spectrum Dynamics D-SPECT includes a special holding plate for the phantom that shows the correct orientation of it in relation to the scanner. The plate and orientation guide are designed for the Deluxe SPECT phantom, so its use rather than the Small SPECT phantom is recommended.

An important note when scanning the SPECT phantom on dedicated cardiac cameras is to recognize that the acquisitions are limited to 180 degrees. Because of this, the setup of the phantom, both internally and in relation to the scanner, is absolutely key in achieving an optimal study. From an internal standpoint, the rods and spheres in the phantom must be coordinated. That is, the largest spheres must be placed over the largest rods and the smallest spheres likewise placed over the smallest rods. Otherwise, you will visualize one (rods/spheres) well but not the other since you’re not scanning completely around the phantom. Setup of the phantom in relation to the scanner is also key as you want the largest rods and spheres to be closest to detectors so that they may be best visualized. Performance of the rest of the specified annual performance tests vary system to system.

Each non-traditional imaging system poses unique testing issues to the qualified medical physicist. Consultations with the manufacturer, service engineer, and ACR accreditation staff will yield great assistance in ensuring a robust testing and quality control program is designed and executed.

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