Don C. Yoo

Fundamentals of PET and PET/CT imaging

In this review, the fundamental principles of fluorodeoxyglucose (FDG) positron emission tomography (PET) and FDG PET/computed tomography (CT) imaging have been described. The basic physics of PET instrumentation, radiotracer chemistry, and the artifacts, as well as normal physiological or benign pathological variants, have been described and presented to the readers in a lucid manner to enable them an easy grasp of the fundamentals of the subject. Finally, we have outlined the current developments in quantitative PET imaging, including dual time point and delayed PET imaging, time‐of‐flight technology in PET imaging and partial volume correction, and global disease assessment with their potential of being incorporated into the assessment of benign and malignant disorders.

Radiofrequency Ablation of Medically Inoperable Stage IA Non–Small Cell Lung Cancer: Are Early Posttreatment PET Findings Predictive of Treatment Outcome?

OBJECTIVE The purpose of this study was to evaluate initial experience with (18)F-FDG PET/CT after pulmonary radiofrequency ablation of stage IA non-small cell lung cancer to determine whether treatment success or residual disease can be predicted with early postablation PET. SUBJECTS AND METHODS Thirty patients with medically inoperable stage IA non-small cell lung cancer (12 men, 18 women; median age, 76 years; range, 60-87 years) underwent outpatient CT-guided radiofrequency ablation over a 33-month period. Mean tumor size was 2.0 cm (range, 1.3-2.9 cm). PET/CT was performed within 60 days before radiofrequency ablation (RFA), within 4 days after RFA, and 6 months after RFA. Metabolic response was categorized as complete response or partial or no response at early post-RFA PET/CT and complete response, partial response, or progressive metabolic disease at 6-month post-RFA PET/CT and was compared with the 1-year clinical event rate (death, disease progression at contrast-enhanced CT, or repeat ablation). RESULTS Early PET/CT images, obtained within 4 days of RFA, were evaluable for 26 patients (23 at 6 months). Patients with a complete metabolic response at early PET/CT had a 1-year event rate of 43%, whereas those with partial or no response or disease progression had a 1-year event rate of 67% (p = 0.27). Patients with a complete metabolic response at 6-month PET/CT had a 1-year event rate of 0%. Those with a partial response and those with disease progression had an overall event rate of 75% (p = 0.001). CONCLUSION Early post-RFA PET/CT is not necessary and 6-month post-RFA PET/CT findings correlate better with clinical outcome at 1 year.

Brain amyloid in preclinical Alzheimer's disease is associated with increased driving risk

Postmortem studies suggest that fibrillar brain amyloid places people at higher risk for hazardous driving in the preclinical stage of Alzheimers disease (AD).

Acute Lower Gastrointestinal Bleeding: Temporal Factors Associated With Positive Findings on Catheter Angiography After 99mTc-Labeled RBC Scanning

OBJECTIVE The objective of the study was to determine if time to positive (TTP), defined as the time from the start of (99m)Tc-labeled RBC scanning to the appearance of a radionuclide blush (considered to be a positive finding for acute lower gastrointestinal bleeding [LGIB]), and lag time (LT), defined as the time from the appearance of a radionuclide blush to the start of catheter angiography (CA), affected the yield of CA for the detection of acute LGIB. MATERIALS AND METHODS TTP and LT were retrospectively evaluated in 120 patients who had positive findings for acute LGIB on (99m)Tc-labeled RBC scanning and subsequently underwent CA for the diagnosis and localization of gastrointestinal bleeding. Two nuclear medicine fellowship-trained radiologists independently reviewed the (99m)Tc-labeled RBC scans. Two fellowship-trained interventional radiologists independently reviewed the angiograms. All data were analyzed using SAS software. RESULTS When a TTP threshold of ≤ 9 minutes was used, the sensitivity, specificity, positive predictive value, and negative predictive value for a positive CA study were 92%, 35%, 27%, and 94%, respectively. In addition, the odds of detecting bleeding on CA increased 6.1-fold with a TTP of ≤ 9 minutes relative to a TTP of > 9 minutes (p = 0.020). A significant inverse relationship was found between LT and a positive CA study (p = 0.041). CONCLUSION TTP and LT impact the rate of positive CA studies. A TTP threshold of ≤ 9 minutes allows the detection of almost all patients who would benefit from CA for treatment and allows a reduction in unnecessary negative CA studies. The likelihood of positive findings on CA decreases with a delay in the performance of CA.

The Evolving Use of Radioiodine Therapy in Differentiated Thyroid Cancer

The incidence of differentiated thyroid cancer has increased worldwide over the last three decades, but thyroid cancer-related mortality remains stable. Until recently, the standard treatment for most thyroid cancers has been near-total thyroidectomy followed by radioiodine remnant ablation. Observational data support lower recurrence rates and improved survival after radioiodine ablation in patients with high-risk cancers; however, a similar benefit has not been established for all patients with thyroid cancer. Risk stratification should be used to identify patients who are likely to benefit from radioiodine ablation and guide therapeutic decisions. For most patients who need radioiodine remnant ablation, preparation for therapy with recombinant human thyroid-stimulating hormone stimulation is as effective as thyroid hormone withdrawal. Lower therapeutic doses of radioiodine are recommended for the majority of thyroid remnant ablations. Higher doses are reserved for advanced disease at initial diagnosis, local recurrences that cannot be treated with surgery alone, and distant metastatic disease.

PET/CT Helps Downgrade an Aggressive-Appearing Rib Mass to a Probable Benign Lesion in a 9-Year-Old Girl.

We present a case of a 9-year-old girl with no significant medical history who developed acute onset of shortness of breath and upper chest pain during cheerleading practice. Laboratory results and physical examination were unremarkable. Chest radiograph and chest CT showed an expansile lytic aggressive-appearing mass within the left sixth rib. Subsequent F-FDG PET/CT showed a left sixth rib lesion that was not hypermetabolic and appeared benign. Biopsy yielded a diagnosis of enchondroma, a benign intramedullary tumor that accounts for 24% of all bone tumors in children as well as adolescents.

Precision Medicine and PET/Computed Tomography in Cardiovascular Disorders

PET/computed tomography (CT) can evaluate the metabolic and anatomic involvement of a variety of inflammatory, infectious, and malignant cardiovascular disorders. PET/CT is useful in evaluating coronary vasculature, hibernating myocardium, cardiac sarcoidosis, cardiac amyloidosis, cerebrovascular disease, acute aortic syndromes, cardiac and vascular neoplasms, cardiac and vascular infections, and vasculitis. Novel targeted radiopharmaceutical agents and novel use of established techniques show promise in diagnosing and monitoring cardiovascular diseases.

Role of PET/CT in Workup of Fever without a Source.

Fever without source is a febrile illness without localizing signs or initial obvious cause. Early workup will often include chest radiography and computed tomography (CT) of the abdomen and pelvis, with or without CT of the chest. To evaluate localizing signs or symptoms or to further evaluate findings from initial studies, targeted imaging according to body part can be performed by using radiography, ultrasonography, CT, or magnetic resonance (MR) imaging. Nuclear medicine studies can provide imaging of the whole body and may be helpful when the clinical and conventional imaging workup findings are negative or equivocal in identifying a source of fever. Nuclear medicine studies can be used to detect pathologic changes early in a disease course, even in the absence of an anatomic abnormality. Gallium 67 scintigraphy, indium 111- and technetium 99m-labeled leukocyte scintigraphy, and fluorine 18 fluorodeoxyglucose positron emission tomography (PET)/CT studies are all useful in the evaluation of fever, but the radiopharmaceutical cost for PET/CT is much lower than that for radiolabeled leukocyte studies. The increased use of bundled payments for inpatient admissions requires updated cost evaluations for the preferred nuclear medicine study. For inpatients in whom the findings from the initial clinical workup and imaging studies are nondiagnostic, PET/CT examination may be preferable to radiolabeled leukocyte studies because of its high sensitivity and lower cost. Negative findings at PET/CT can be helpful in excluding a suspected site of infection, and positive findings at PET/CT can be helpful in confirming a suspected site of infection or in identifying an unexpected cause of fever. (©)RSNA, 2016.

Controversy Over Radioiodine Ablation In Thyroid Cancer: Who Benefits?

Recent studies have proposed that overdiagnosis is probably the principal cause of the increased incidence of thyroid cancer. The controversy around radioiodine ablation is complicated by the ever increasing numbers of small, low-risk thyroid cancers being diagnosed. This article examines the history and evolving epidemiology of the disease and treatment.

DISRUPTION OF CHOLINERGIC NEUROTRANSMISSION, WITHIN A COGNITIVE CHALLENGE PARADIGM, PREDICTS Aβ-RELATED COGNITIVE IMPAIRMENT IN PRECLINICAL ALZHEIMER’S DISEASE AFTER A 27-MONTH DELAY INTERVAL

Figure 1. Performance on the International Shopping List (ISLT) Delayed Recall Task, by participants who either failed the scopolamine challenge test (SCT) at baseline (N 1⁄4 28, at end of study) vs. those who passed the SCTat baseline (N1⁄4 30, at end of study), modeled over all four study visits. Dark lines indicate group mean scores at each visit, with SE bars provided. Both betweenand within-subject variation is represented in each group, by displaying individual subject change over time, with each case yoked to the group baseline mean score. Danielle Goldfarb, Peter J. Snyder, Paul Maruff, Cl audia Y. Santos, Brian R. Ott, Stephen Salloway, Don C. Yoo, Richard B. Noto, Jessica Alber, Louisa I. Thompson, Alex Song, Alpert Medical School of Brown University, Providence, RI, USA; University of Rhode Island, Kingston, RI, USA; The Florey Institute of Neuroscience and Mental Health, Melbourne, Australia; Cogstate Ltd., Melbourne, Australia; Lifespan, Providence, RI, USA; Butler Hospital, Providence, RI, USA; Brown University, Providence, RI, USA. Contact e-mail: dagoldfarb9@gmail.com