COVID-19: Findings in nuclear medicine from head to toe.

COVID-19 is a multisystemic disease, and hence its potential manifestations on nuclear medicine imaging can extend beyond the lung. Therefore, it is important for the nuclear medicine physician to recognize these manifestations in the clinic. While FDG-PET/CT is not indicated routinely in COVID-19 evaluation, its unique capability to provide a functional and anatomical assessment of the entire body means that it can be a powerful tool to monitor acute, subacute, and long-term effects of COVID-19. Single-photon scintigraphy is routinely used to assess conditions such as pulmonary embolism, cardiac ischemia, and thyroiditis, and COVID-19 may present in these studies. The most common nuclear imaging finding of COVID-19 vaccination to date is hypermetabolic axillary lymphadenopathy. This may pose important diagnostic and management dilemmas in oncologic patients, particularly those with malignancies where the axilla constitutes a lymphatic drainage area. This article aims to summarize the relevant literature published since the beginning of the pandemic on the intersection between COVID-19 and nuclear medicine.

Molecular imaging in oncology: Common PET/CT radiopharmaceuticals and applications.

PET/CT is a commonly used modality in cancer imaging, as it can help in diagnosis, staging and assessment of treatment response in many cancer types. A better understanding of the tumor microenvironment and identification of multiple selective targets are promoting further investigation into different radiotracers for diagnosis and therapy. In the past few decades many radiopharmaceuticals have emerged for specific oncologic indications providing superior detection rate than some morphologic modalities. The purpose of this review is to provide an update on the most current radiopharmaceuticals used in cancer imaging including the mechanism of action, indications and pitfalls.

PET-CT reveals increased intestinal glucose uptake after gastric surgery.

BACKGROUND: Mechanisms of metabolic improvement after bariatric surgery remain incompletely understood. Intestinal glucose uptake is increased after gastric bypass in rodents, potentially contributing to reduced blood glucose and type 2 diabetes remission. OBJECTIVE: We assessed whether intestinal glucose uptake is increased in humans after gastric surgery. SETTING: University Hospital, United States. METHODS: In a retrospective, case-control cohort study, positron emission tomography-computerized tomography scans performed for clinical indications were analyzed to quantify intestinal glucose uptake in patients with or without history of gastric surgery. We identified 19 cases, defined as patients over age 18 with prior gastric surgery (Roux-en-Y gastric bypass [n = 10], sleeve gastrectomy [n = 1], or Billroth I [n = 2] or II gastrectomy [n = 6]), and 43 controls without gastric surgery, matched for age, sex, and indication for positron emission tomography-computerized tomography. Individuals with gastrointestinal malignancy or metformin treatment were excluded. Images were obtained 60 minutes after 18F-fluorodeoxyglucose injection (4.2 MBq/kg), and corrected by attenuation; noncontrast low-dose computerized tomography was obtained in parallel. Fused and nonfused images were analyzed; standardized uptake values were calculated for each region by volumes of interest at the region of highest activity. RESULTS: Both standardized uptake values maximum and mean were significantly increased by 41% to 98% in jejunum, ascending, and transverse colon in patients with prior gastric surgery (P < .05 versus controls). CONCLUSION: Intestinal glucose uptake is increased in patients with prior gastric surgery. Prospective studies are important to dissect the contributions of weight loss, dietary factors, and systemic metabolism, and to determine the relationship with increased insulin-independent glucose uptake and reductions in glycemia.

Imaging the posterior mediastinum: a multimodality approach.

The posterior mediastinum contains several structures that can produce a wide variety of pathologic conditions. Descending thoracic aorta, esophagus, azygos and hemiazygos veins, thoracic duct, lymph nodes, adipose tissue, and nerves are all located in this anatomical region and can produce diverse abnormalities. Although chest radiography may detect many of these pathologic conditions, computed tomography and magnetic resonance are the imaging modalities of choice for further defining the relationship of posterior mediastinal lesions to neighboring structures and showing specific imaging features that narrow the differential diagnosis. This review emphasizes modality-related answers to morphologic questions, which provide precise diagnostic information.

Rifaximin suppresses background intestinal 18F-FDG uptake on PET/CT scans.

BACKGROUND: Identification of cancer or inflammatory bowel disease in the intestinal tract by PET/computed tomography (CT) imaging can be hampered by physiological uptake of F-fluorodeoxyglucose (F-FDG) in the normal colon. Previous work has localized this F-FDG uptake to the intestinal lumen, predominantly occupied by bacteria. We sought to determine whether pretreatment with an antibiotic could reduce F-FDG uptake in the healthy colon. PATIENTS AND METHODS: Thirty patients undergoing restaging PET/CT for nongastrointestinal lymphoma were randomly selected to receive rifaximin 550 mg twice daily for 2 days before their scan (post-rifaximin). Their PET/CT images were compared with those from their prior study (pre-rifaximin). Cecal maximum standard uptake value (SUVmax) and overall colonic F-FDG uptake were compared between scans. All PET/CT images were blindly scored by a radiologist. The same comparison of sequential scans was also undertaken in 30 patients who did not receive antibiotics. RESULTS: Thirty post-rifaximin scans were compared with 30 pre-rifaximin scans in the same patients. SUVmax in the cecum was significantly lower in the patient's post-rifaximin scans than in their pre-rifaximin scans (P=0.002). The percentage of scans with greater than grade 1 colonic F-FDG uptake was significantly lower in the post-rifaximin scans than in the pre-rifaximin scans (P<0.05). In contrast, there was no significant difference in the paired sequential scans from control patients, nor a reduction in the percentage of scans with greater than grade 1 colonic F-FDG uptake. CONCLUSION: This pilot study shows that treatment with rifaximin for 2 days before PET/CT scanning can significantly reduce physiological F-FDG uptake in the normal colonic lumen.

Long-term follow-up assessment after the arterial switch operation for correction of dextro-transposition of the great arteries by means of exercise myocardial perfusion-gated SPECT.

The arterial switch operation (ASO) is the preferred technique for correcting transposition of the great arteries, but translocation and reimplantation of the coronary arteries can produce myocardial ischemia. This report aims to describe the authors' experience with exercise single-photon emission computed tomography (SPECT) used to evaluate myocardial perfusion. Exercise-rest gated-myocardial perfusion SPECT was performed for 69 patients (49 boys; median age, 9 years; 5th percentile [6.4 years] to 95th percentile [15.6 years]), 64 of whom were asymptomatic 9.98 ± 3.20 years after ASO. During exercise testing, the patients reached 9.85 ± 3.05 metabolic equivalents (METs) and a median heart rate of 160 beats per minute (bpm), 5th percentile (106 bpm) to 95th percentile (196 bpm). Whereas 61 patients (88.41 %) had normal myocardial perfusion, 2 patients (2.9 %) had reversible defects, and 6 patients (8.7 %) had fixed defects. All the patients with perioperative ischemic complications (4/4, 100 %) had myocardial perfusion defects, whereas four patients (4/65, 6.15 %) without ischemic complications had abnormal perfusion (p = 0.0005). Age at the time of surgery did not differ significantly (p = 0.234) between the patients with perfusion defects and those with normal study results. No significant difference was observed between the patients who had an A coronary pattern (left coronary artery originating from the left sinus and the right coronary artery originating from the right sinus, n = 47) and those who had a non-A coronary pattern (n = 22) (p = 1). The high rate for normality of exercise myocardial perfusion in our study suggests that myocardial perfusion gated-SPECT should be reserved for patients who have experienced perioperative ischemic complications or those with symptoms, at least during the first 10 years after the surgery.

Imaging findings of Pott's disease.

Tuberculosis (TB) continues to be an important public health problem in developed countries especially in deprived socioeconomic groups, older people, immunocompromised patients, drug-therapy resistant cases and the immigrant population. The spine is the most frequent location of musculoskeletal TB. The wide range of clinical presentations results in difficulties and delays in diagnosis. Advanced disease mimics other infections and malignancy. The diagnosis of spinal infections relies on three main factors: clinical symptoms, imaging and bacteriological culture. Advanced imaging such as Magnetic Resonance Imaging (MRI), Multidetector Computed Tomography (MDCT) and Fluor18-Deoxiglucose Positron Emission Tomography combined with CT (F-18 FDG PET-CT) demonstrate lesion extent, serve as guide for biopsy with aspiration for culture, assist surgery planning and contribute to follow-up. Diagnosis of TB cannot be established solely on the basis of clinical tests or imaging findings and biopsy may be required. Differential diagnosis between tuberculous and pyogenic spondylitis is of clinical importance, but may be difficult on the basis of radiological findings alone. Findings not pathognomonic but favoring tuberculous etiology include: slow progression of lesions with late preservation of disk space, involvement of several contiguous segments, large intraosseous and paraspinal abscesses containing calcifications, and body collapse with kyphotic deformity. In this essay the highlights of TB imaging are reviewed through published literature. In addition, we review retrospectively the radiological findings of 48 patients with tuberculous spondylitis treated from 1993 to 2010. There were 23 male and 25 female patients with a mean age of 53 years.