PET scanning using a gamma camera describes the use of a PET radiotracer, (i.e., radio-labeled 2-fluoro-2 deoxy-D-glucose [FDG]), in conjunction with a SPECT gamma camera, instead of a dedicated PET scanner.  A dedicated PET scanner consists of multiple detectors arranged in a full or partial ring around the patient, permitting the simultaneous detection of the high-energy paired positrons that are emitted at 180 degrees from one another.   SPECT gamma cameras are conventionally used to provide scintigraphic studies, such as bone scans or cardiac thallium studies.  When used in conjunction with FDG, specially equipped SPECT cameras can provide images reflecting the metabolic activity of tissues, similar to PET scanning.  

NOTE:  This document describes a variant to a PET scan and does not address conventional SPECT scanning, which is addressed separately in RAD.00023 Single Photon Emission Computed Tomography (SPECT) Scans and Scintimammography.

For additional indications for conventional PET and PET/CT fusion testing, see RAD.00002 Positron Emission Tomography (PET) and PET/CT Fusion.

Investigational and Not Medically Necessary: 

All applications of PET scanning with a gamma camera are considered investigational and not medically necessary.

A key consideration in the evaluation of PET scans using gamma cameras is the fact that the lower number of detectors in the SPECT approach, compared to the full or partial ring of detectors used in PET imaging, will result in a relative loss of sensitivity and resolution.  Both oncologic and cardiac applications of this technology have been investigated.

Oncologic Applications:
A variety of studies, focusing on the oncologic applications of PET scanning using gamma cameras, have consistently reported a decreased sensitivity for smaller lesions (<2 cm in diameter), compared to conventional PET scanning.  There is inadequate data comparing the diagnostic performance of PET scanning using gamma cameras to either CT scans or MRI.  In 2001, the Centers for Medicaid and Medicare Services (CMS) published an analysis of the data regarding oncologic applications of PET scans using gamma cameras.  This analysis offered the following conclusion:

There are no clear, comparative, broad indication studies, and only very small, indication-specific studies to compare camera-based PET to full-ring PET.  Further, these studies are designed to focus mainly on the intrinsic performance of the scanners, not the evaluation of reconstruction and processing algorithms on the sensitivity and specificity of different systems under conditions of actual clinical use.  In other words, after an exhaustive search for empirical data, there is no body of evidence that attests to the medical benefit associated with use of camera-based PET that is comparable to the literature used to arrive at the December 15, 2000 decision memorandum for full-ring PET.  The extension of that decision memorandum to camera-based systems, while anecdotally supported by nuclear medicine experts, cannot be clearly justified, based on existing clinical and scientific data.

In fact, review of the existing literature on camera-based PET leads to the conclusion, present in several articles, that these systems miss a significant number of small and medium-sized malignant lesions.  Because of the limited size of the studies and other methodologic weaknesses, it is not possible to make confident estimates of the frequency with which these different systems produce false positive or false negative results.  Furthermore, it is not possible to determine the clinical significance of diagnostic errors that might result from use of these PET technologies.  However, given the intended diagnostic role for oncologic uses of PET, it is likely that inaccurate results provided by these imaging systems could lead to errors in treatment, such as early termination of chemotherapy or unnecessary surgical intervention.  Without better studies that provide more confident estimates of the sensitivity and specificity from camera-based PET systems, it may not be possible for clinicians to properly interpret the finding from these imaging studies (CMS, 2001).

Cardiac Applications:
There is inadequate data regarding the use of PET scanning with gamma cameras in the evaluation of coronary perfusion defects.  The use of this imaging modality to assess myocardial viability has been reported by two studies.  Srinivasan and colleagues reported on a case series of 28 patients with chronic coronary artery disease and left ventricular dysfunction.  All patients underwent PET scanning using a gamma camera, conventional PET, and thallium SPECT studies.  Conventional PET served as the gold standard.   Hasegawa and colleagues compared PET scanning with a gamma camera and conventional PET scanning, as techniques to evaluate myocardial viability in 25 patients.  Both studies suggested some utility for gamma-camera PET scanning for the narrow indication of assessment of myocardial viability.  However, the small sample size in these studies does not allow for definitive conclusions (Srinivasan, 1998; Hasegawa, 1999).       

Neurologic Disorders:
PET scans have been widely used in the evaluation of neurological disorders, ranging from epilepsy to dementias.  There is inadequate data to compare conventional PET with PET scanning with a gamma camera for neurological disorders.

Dedicated PET scanners consist of multiple detectors arranged in a full or partial ring around the patient, permitting the simultaneous detection of the high-energy paired photons that are emitted at 180 degrees from one another.  The clinical value of PET scans is related both to the ability to image the relative metabolic activity of target tissues and the resolution associated with PET scanners.  The requirement of on-site manufacture of the FDG and the expense of the dedicated PET scanner itself has limited the widespread availability of PET scanning.  However, radiolabeled FDG has a relatively long half-life of 110 minutes, permitting off-site manufacture at distribution centers with transport to nearby facilities.  Thus, the lack of PET scanners may be emerging as the critical limiting factor to further diffusion of PET imaging.  In response, researchers have begun to investigate whether the more readily available SPECT cameras, routinely used to detect low-energy photons, could be adapted for use to detect higher energy photons emitted from positrons.  An additional technical challenge is the use of sodium iodide crystals, which scintillate in response to bombardment by photons.  In SPECT cameras, these crystals have been optimized to detect lower energy photons, used in routine nuclear medicine studies and not the high-energy photons associated with FDG.  These technical issues raise questions regarding the diagnostic performance of FDG-SPECT, in comparison to conventional PET scanning.  Oncologic and cardiac applications have been most thoroughly studied.

Positron Emission Tomography (PET): an imaging technique that measures the concentration of chemicals injected into the body, and provides images of the chemical function of body parts of interest

The following codes for treatments and procedures applicable to this document are included below for informational purposes.  Inclusion or exclusion of a procedure, diagnosis or device code(s) does not constitute or imply member coverage or provider reimbursement policy.  Please refer to the member's contract benefits in effect at the time of service to determine coverage or non-coverage of these services as it applies to an individual member.

When services are Investigational and Not Medically Necessary:
For the procedure code listed below in all instances, or when the code describes a procedure indicated in the Position Statement section as investigational and not medically necessary.

Peer Reviewed Publications:

1. Delbeke D, Patton JA, Martin WH, Sandler MP.   FDG PET and dual-head gamma camera positron coincidence detection imaging of suspected malignancies and brain disorders.  J Nucl Med. 1999; 40(1):110-117. 
2. Hasegawa S, Uehara T, Yamaguchi H, et al.  Validity of 18F-fluorodeoxyglucose imaging with a dual-head coincidence gamma camera for detection of myocardial viability.  J Nucl Med. 1999; 40(11):1884-1892.
3. Martin WH, Delbeke D, Patton JA, Sandler MP.   Detection of malignancies with SPECT versus PET, with 2-fluorine-18) fluoro-2-deoxy-d-glucose.  Radiology. 1996; 198(1):225-231. 
4. Shreve PD, Steventon RS, Deters EC, et al.  Oncologic diagnosis with 2-[fluorine-18] fluoro-2-deoxy-D-glucose imaging: dual head coincidence gamma camera versus positron emission tomographic scanner.  Radiology. 1998; 207(2):431-437.
5. Srinivasan G, Kitsiou AN, Bachrach SL, et al. [18F] fluorodeoxyglucose single photon emission computed tomography: can it replace PET and thallium SPECT for the assessment of myocardial viability?  Circulation. 1998; 97(9):843-850. 
6. Tatsumi M, Yutani K, Watanabe Y, et al.   Feasibility of fluorodeoxyglucose dual-head gamma camera coincidence imaging in the evaluation of lung cancer: Comparison with FDG PET.  J Nucl Med. 1999; 40(4):566-573. 
7. Udelson JE.   Steps forward in the assessment of myocardial viability in left ventricular dysfunction.  Circulation. 1998; 97(9):833-838. 
8. Weber W, Young C, Abdel-Dayem HM, et al.   Assessment of pulmonary lesions with 18F-fluorodeoxyglucose positron imaging using coincidence mode gamma cameras.  J Nucl Med. 1999; 40(4):574-578. 
9.  Yutani K, Tatsumi M, Shiba E, et al. Comparison of dual-head coincidence gamma camera FDG imaging with FDG PET in detection of breast cancer and axillary lymph node metastasis. J Nucl Med. 1999; 40(6):1003-1008. 

Government Agency, Medical Society, and Other Authoritative Publications:

1. Centers for Medicare and Medicaid Services. National Coverage Determination for PET Scans. NCD #220.6. Effective April 3, 2009. Available at: https://www.cms.hhs.gov/mcd/viewdecisionmemo.asp?from2=viewdecisionmemo.asp&id=218&.  Accessed on April 27, 2009.

Camera Based PET Scans
FDG-SPECT
Gamma Cameras, PET Scanning Using
Metabolic SPECT
PET Scanning Using Gamma Cameras