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PET Imaging Arrives

Now available at the Dean Clinic, Monroe Clinic and Upland Hills Health, positron emission tomography (PET scanning) has exploded into the medical imaging arena. Because PET differs from other imaging modalities by imaging differing levels of metabolic function, PET has the ability to specifically distinguish normal from abnormal tissue. PET particularly excels in the fields of oncology (cancer), neurology and cardiology.

While PET scanning has been available since the 1980’s, only recently has widespread clinical use blossomed. The rise in use of PET scanning can be attributed to a combination of growing clinical evidence of its usefulness, improved availability of the radioactive tracers, and reimbursement by both private insurers and Medicare.

It is in oncologic (cancer) imaging that PET has its greatest impact. Because many tumors exhibit accelerated metabolism of glucose, intravenous injection of F-18 fluorodeoxyglucose (FDG) accumulates in areas of tumor that can then be imaged with a special camera. Other applications in cancer include gauging the response to therapy, and distinguishing cancer from non-cancerous findings at imaging. Examples of this situation include distinguishing radiation therapy related enhancement or scarring from tumor, or distinguishing a benign from cancerous pulmonary nodule.

Applications outside the realm of cancer include diagnosis of Alzheimer’s Disease, location of seizure foci in the brain, and determining viable heart tissue in candidates for cardiac bypass surgery.

Applications are expanding rapidly and go beyond those currently reimbursed by Medicare. Currently reimbursed applications of FDG PET by Medicare (CMS) include:

  • Colorectal cancer: initial diagnosis, staging, re-staging
  • Lung cancer (non-small cell): initial diagnosis, staging, re-staging
  • Lymphoma: initial diagnosis, staging, re-staging
  • Esophageal cancer: initial diagnosis, staging, re-staging
  • Breast cancer: for staging, re-staging
  • Head and neck cancers (excluding thyroid): initial diagnosis, staging, re-staging
  • Melanoma: initial diagnosis, staging, re-staging
  • Solitary Pulmonary Nodule
  • Myocardial viability: after non-conclusive SPECT study
  • Refractory Seizures: pre-surgical evaluation

Though not yet approved by Medicare for reimbursement, PET scanning in cases of cancers of the pancreas, ovary and cervix has been shown useful in clinical practice. PET has the potential for modifying long held staging protocols in many of these tumors.

PET scans for cancer must be compared with CT scans to appropriately correlate the findings.

A link to a list of medical journal articles describing clinical results of PET imaging can be found at:

Case Examples:

Abnormal activity representative of recurrent melanoma(arrowhead) in left salivary (parotid) gland in patient who had previously resected head and neck melanoma.

Same melanoma patient with spread of tumor to lung (arrowhead)

Multiple sites of abnormal tumor activity in patient with lymphoma, including axillary nodes (asterisks), cervical chain (arrowhead). Multifocal areas of abnormal activity representing tumor is also present in the abdomen and inguinal (groin) regions.

Same lymphoma patient demonstrating tumor in paratracheal region (arrowhead), and retroperitoneum (asterisk).

Abnormal activity in lung (arrowhead) indicates malignancy (cancer) with a specificity of 82% and sensitivity of 94%. Thus, decision on whether to biopsy or follow up a pulmonary nodule can be guided by findings at PET imaging. Asterisk indicates localized collecting system dilation of kidney.

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