Amir Abdelmalik

Whole-Body 18F-FDG PET/CT: The Need for a Standardized Field of View—A Referring-Physician Aid

PET/CT fusion of anatomic and functional imaging modalities is in evolution, with rapid clinical dissemination. The imaged field of view (FOV) selected for whole-body PET/CT protocols is not standardized and varies by institution. Misuse of the term whole body, as well as the pressure to increase the number of daily studies by reducing scanning time, contributes to the lack of standardization. The purpose of this study was to evaluate variations in the FOV and arm positioning selected for whole-body PET/CT protocols at private, as well as academic, PET centers. Methods: Two hundred consecutive whole-body 18F-FDG PET/CT studies were retrospectively reviewed for FOV: 50 studies from a private stationary site, 50 studies from 2 separate private mobile sites (25 consecutive studies from each), and 100 studies from a stationary university site: 50 before and 50 after implementation of a true whole-body protocol covering the top of the head through the bottom of the feet. Data were categorized into 5 different anatomic scan lengths: base of skull to upper thigh, base of skull to mid thigh, top of head to upper thigh, top of head to mid thigh, and true whole-body. Studies were further categorized into 2 patient arm positions: up and down. Results: The private stationary and mobile sites had only 2 categories of anatomic scan lengths identified: base of skull to mid thigh, and top of head to upper thigh. At the university site, before implementation of a true whole-body protocol, the 5 different anatomic scan lengths were identified; after implementation, only the true whole-body scan length was identified. Patients’ arms in the private stationary sites were down 100% of the time. At the private mobile sites, patients’ arms were up 72% of the time and down 28% of the time. At the university site, patients’ arms were up 54% of the time and down 46% of the time. The same site, after implementation of a true whole-body protocol, had patients’ arms up 58% of the time and down 42% of the time. Overall, patients’ arms were up 46% of the time and down 54% of the time. Conclusion: The continued use of the term whole body is misleading because frequently it may not include the brain, skull, or significant portions of the upper and lower extremities. PET/CT anatomic scan length varied not only from one site to the next but also within individual sites. The Centers for Medicare and Medicaid Services have different current procedural terminology codes distinguishing between base of skull to upper thigh and true whole-body covering the top of the skull to the bottom of the feet, thus underscoring the need to standardize the terminology used in describing PET/CT scan length.

The Incremental Added Value of Including the Head in 18F-FDG PET/CT Imaging for Cancer Patients

Purpose: To assess the value of extending the routinely used base-of-skull (BOS) to upper-thigh field of view (FOV) to include the head on 18F-FDG PET/CT in cancer patients. Methods: We retrospectively reviewed 1000 consecutive top-of-head to foot PET/CT studies. Abnormalities above BOS were categorized as unsuspected or known and were correlated with pathology, MRI/CT, and clinical follow-up. Results: Of the 1000 patients, 102 (10.2%) had potentially significant findings above BOS. Of these, 70/102 (69%) were known and 32/102 (31%) were unsuspected. Of the patients with unsuspected findings, follow-up data was unavailable in 7/32 (22%) and abnormalities were confirmed in 25/32 (78%). Of the 25 confirmed unsuspected findings, 4/25 (16%) were false positives and 21/25 (84%) were true positives. Of these, 13/21 (62%) were confirmed metastatic, and 8/21 (38%) were benign. Unsuspected finding of brain metastasis changed the management in 11/13 (85%) and staging in 4/13 (31%). Conclusion: Including the head in PET/CT FOV incidentally detected clinically significant findings in 2.1% (21/1000) of patients. The detection of previously unsuspected metastasis had significant impact on patient management and provided more accurate staging.

FDG PET/CT incidental diagnosis of a synchronous bladder cancer as a fourth malignancy in a patient with head and neck cancer.

A 74-year-old man with 40-year history of smoking and known history of chronic lymphocytic leukemia and cutaneous T-cell lymphoma underwent FDG PET/CT examination for a recent diagnosis of squamous cell carcinoma diagnosed from right frontal crown and left posterior ear skin biopsy. PET images revealed multiple FDG-avid lesions in the head and neck, highly suspicious for nodal metastases. Reviewing CT portion of PET/CT examination revealed a hyperattenuating density in the posterior bladder wall. This lesion was not noticed initially due to the intense physiologic bladder uptake. On lowering the intensity, this lesion showed intense FDG avidity on the PET portion of the examination. Cytoscopic biopsy revealed low-grade papillary urothelial cell carcinoma.

Squamous cell carcinoma of the bulbar conjunctiva seen on F-18 FDG PET/CT.

A 65-year-old man with left orbital mass and recent vision loss underwent FDG PET/CT, which showed intensely FDG-avid anterior left orbital mass invading the periorbital soft tissue. Enlarged left retromandibular, mediastinal, and abdominal lymph nodes with intense FDG uptake were suspicious for malignancy. Left orbital exenteration revealed moderately differentiated squamous cell carcinoma. Fine needle aspiration of mediastinal lymph nodes revealed inflammatory processes; therefore, the left retromandibular lymph node was felt to be benign and no biopsy was performed. However, follow-up PET/CT demonstrated significant increase in size and uptake of the left retromandibular lymph node, which was proven metastatic in subsequent biopsy.