[18F]FDG uptake in axillary lymph nodes and deltoid muscle after COVID-19 mRNA vaccination: a cohort study to determine incidence and contributing factors using a multivariate analysis.

PURPOSE: Reactive FDG uptake in the axillary lymph nodes (ALN) and deltoid muscle (DM) after COVID-19 mRNA vaccination has been recognized, although the actual situation in the Japanese population remains unknown. To determine the incidence of reactive FDG uptake and its contributing factors, we retrospectively studied a cohort of subjects who were vaccinated at our hospital. METHODS: Whole-body FDG-PET/CT examinations performed in 237 subjects out of 240 subjects with a definite history of COVID-19 vaccination (BNT162b2; BioNTech-Pfizer) were analyzed. Positivity and SUVmax of FDG uptake in the ALN and DM ipsilateral to vaccination, various subject characteristics, and the grade of the pathological FDG-PET/CT findings were evaluated using a multivariate analysis. RESULTS: FDG uptake in the ALN and DM ipsilateral to vaccination was seen in about 60% of the subjects even soon (0-4 days) after the first vaccination, with percentages reaching 87.5% and 75.0%, respectively, after the second vaccination. DM uptake had almost disappeared at around 2 weeks, while ALN uptake persisted for 3 weeks or longer. A multivariate analysis showed that a short duration since vaccination, a younger age, a female sex, and a low FDG-PET/CT grade (minimal pathological FDG uptake) contributed significantly to positive ALN uptake, while a short duration since vaccination and a female sex were the only significant contributors to positive DM uptake. This study is the first to identify factors contributing to positive FDG uptake in ALN and DM after COVID-19 vaccination. CONCLUSION: A high incidence of FDG uptake in ALN and DM was observed after vaccination. ALN uptake seemed to be associated with a younger age, a female sex, and minimal pathological FDG uptake. After vaccination, an acute inflammatory reaction in DM followed by immune reaction in ALN linked to humoral immunity may be speculated.

Characteristic Radiological Features of Retrospectively Diagnosed Pancreatic Cancers.

OBJECTIVES: The aim of this study was to assess the characteristic radiological features of early-stage pancreatic cancer (PC). METHODS: Between 2009 and 2016, 510 PC patients were selected from our hospital cancer registry database based on International Classification of Diseases for Oncology-3 (C25). Among them, 64 patients (42 males and 22 females; median age, 74 [range, 59-91]) had received repeated abdominal radiological examinations before their diagnosis of PC and were retrospectively investigated for specific radiological findings. The subjects underwent the following imaging examinations: computed tomography, magnetic resonance imaging, and fluoroglucose-positron emission tomography. RESULTS: Characteristic radiological features before diagnosis of PC were classified into the following 9 features: pancreatic duct ectasia (n = 16), focal low-density area (n = 15), change of cyst size (n = 8), localized tissue atrophy (n = 7), distal atrophy (n = 4), mass in pancreatic lipomatosis tissue (n = 2), mass concomitant with the already known cyst (n = 2), protrusion (n = 1), and parenchymal disproportion (n = 1). Fifty-three cases (84%) had more than one characteristic radiological feature before diagnosis of PC, and their median observation period until diagnosis was 24 (range, 1-120) months. CONCLUSIONS: The 9 characteristic radiological features provide an opportunity to diagnose PC at an early stage.

Magnetic resonance imaging of prostate carcinoma using phased-array coils: therapeutic effect and recurrence.

Magnetic resonance imaging with phased-array coils was performed in patients with prostate carcinoma before and after hormonal therapy, radiation therapy or radical prostatectomy to evaluate therapeutic effect and recurrence. After hormonal therapy, the prostate gland, seminal vesicle and primary site of tumor usually decrease in size with variable T2 hypointensity. Recurrent or residual tumors after hormonal therapy usually represent T2 hyperintense lesions compared to the hypointensity of the surrounding tissues. Changes of metastatic sites after therapy were also demonstrated.

Dynamic MRI for distinguishing high-flow from low-flow peripheral vascular malformations.

OBJECTIVE: The purpose of our study was to assess the usefulness of dynamic MRI in distinguishing high-flow vascular malformations from low-flow vascular malformations, which do not need angiography for treatment. SUBJECTS AND METHODS: Between September 2001 and January 2003, 16 patients who underwent conventional and dynamic MRI had peripheral vascular malformations (six high- and 10 low-flow). The temporal resolution of dynamic MRI was 5 sec. Time intervals between beginning of enhancement of an arterial branch in the vicinity of a lesion in the same slice and the onset of enhancement in the lesion were calculated. We defined these time intervals as "artery-lesion enhancement time." Time intervals between the onset of enhancement in the lesion and the time of the maximal percentage of enhancement above baseline of the lesion within 120 sec were measured. We defined these time intervals as "contrast rise time" of the lesion. Diagnosis of the peripheral vascular malformations was based on angiographic or venographic findings. RESULTS: The mean artery-lesion enhancement time of the high-flow vascular malformations (3.3 sec [range, 0-5 sec]) was significantly shorter than that of the low-flow vascular malformations (8.8 sec [range, 0-20 sec]) (Mann-Whitney test, p < 0.05). The mean maximal lesion enhancement time of the high-flow vascular malformations (5.8 sec [range, 5-10 sec]) was significantly shorter than that of the low-flow vascular malformations (88.4 sec [range, 50-100 sec]) (Mann-Whitney test, p < 0.01). CONCLUSION: Dynamic MRI is useful for distinguishing high-flow from low-flow vascular malformations, especially when the contrast rise time of the lesion is measured.

CT of internal hernias.

Computed tomography (CT) plays an important role in diagnosis of acute intestinal obstruction and planning of surgical treatment. Although internal hernias are uncommon, they may be included in the differential diagnosis in cases of intestinal obstruction, especially in the absence of a history of abdominal surgery or trauma. CT findings of internal hernias include evidence of small bowel obstruction (SBO); the most common manifestation of internal hernias is strangulating SBO, which occurs after closed-loop obstruction. Therefore, in patients suspected to have internal hernias, early surgical intervention may be indicated to reduce the high morbidity and mortality rates. In a study of 13 cases of internal hernias, nine different types of internal hernias were found and the surgical and radiologic findings were correlated. The following factors may be helpful in preoperative diagnosis of internal hernias with CT: (a) knowledge of the normal anatomy of the peritoneal cavity and the characteristic anatomic location of each type of internal hernia; (b) observation of a saclike mass or cluster of dilated small bowel loops at an abnormal anatomic location in the presence of SBO; and (c) observation of an engorged, stretched, and displaced mesenteric vascular pedicle and of converging vessels at the hernial orifice.

Serial diffusion-weighted MRI of Creutzfeldt-Jakob disease.

OBJECTIVE: The objective of our study was to evaluate the clinical usefulness of MRI findings, including diffusion-weighted imaging, in relation to the clinical signs and symptoms of Creutzfeldt-Jakob disease (CJD). MATERIALS AND METHODS: We reviewed nine cases of CJD in which MRI was performed from the early to terminal phase of the disease. MRI findings were correlated before (early phase) and after (intermediate phase) the onset of the characteristic clinical findings of myoclonus and periodic synchronous discharges on electroencephalograms. The chronologic changes in imaging findings were followed from the akinetic mutism to the terminal phase of the disease (terminal phase). T2-weighted images had been obtained in all the patients, and diffusion-weighted images and FLAIR images had been obtained in six patients. We evaluated the images for the presence and location of abnormal signal intensities. RESULTS: During the early phase, the T2-weighted images showed no abnormal findings. The diffusion-weighted images, however, revealed abnormal high signal intensities in the cortex in all patients and in the basal ganglia in five patients. In two cases, there were abnormal signals on FLAIR images that corresponded to diffusion-weighted imaging abnormalities. During the intermediate phase, the area of the high signal intensities on the diffusion-weighted images had expanded and progressive cerebral atrophy had become apparent. During the terminal phase, abnormal high signal intensities in the cerebral cortex and basal ganglia on the diffusion-weighted images in one patient disappeared. CONCLUSION: Diffusion-weighted imaging is extremely useful in detecting CJD during the very early phase-even before the onset of characteristic clinical findings.

Acute cerebral infarction: effect of JPEG compression on detection at CT.

PURPOSE: To evaluate the effect of Joint Photographic Experts Group (JPEG) compression ratios of 10:1 and 20:1 on detection of acute cerebral infarction at computed tomography (CT). MATERIALS AND METHODS: CT images obtained in 25 patients with acute cerebral infarction and 25 patients with no lesions were compressed by means of a JPEG algorithm at ratios of 10:1 and 20:1. Normal and abnormal sections (on original and compressed images) were reviewed by using a color soft-copy computed monochrome cathode ray tube monitor. Five observers rated the presence or absence of a lesion with a 50-point scale (0, definitely absent; 25, equivocal; and 50, definitely present). Diagnostic accuracy was evaluated with receiver operating characteristic (ROC) curve analysis. Significant difference was defined as a P value less than.05 for the area tested with a two-tailed paired Student t test. RESULTS: At ROC analysis, no statistically significant difference was detected for all cases considered together (Az [area under the ROC curve] = 0.887 +/- 0.038 [mean +/- SD] on noncompressed images, Az = 0.897 +/- 0.038 on 10:1 compressed images, and Az = 0.842 +/- 0.073 on 20:1 compressed images; P >.05). CONCLUSION: JPEG compression at ratios of 10:1 and 20:1 was tolerated in the detection of acute cerebral infarction at CT.

A prospective survey of delayed adverse reactions to iohexol in urography and computed tomography.

We investigated 7505 inpatients who underwent intravenous urography or contrast-enhanced computed tomography to assess risk factors for delayed adverse drug reactions to iohexol, a non-ionic iodinated contrast medium. Focusing on delayed adverse reactions, all adverse events were prospectively investigated for 7 days after injection of iohexol. To explore the relevant risk factors, the relationship between occurrence of adverse reactions to iohexol and 17 different variables was evaluated by logistic regression analysis. To assess the influence of seasonal factors, adverse reactions were separately evaluated during two periods: February to April (the pollinosis period in Japan) and July to September (the non-pollinosis period). The prevalence of delayed adverse events and delayed adverse reactions was 3.5 and 2.8%, respectively, whereas the prevalence of adverse events and adverse reactions was 5.7 and 5.0%, respectively. Multivariate analysis showed that six parameters had a significant influence on delayed adverse reactions to iohexol, including (a) a history of allergy, (b) season, (c) radiographic procedure, (d) age, (e) concomitant surgery or other invasive procedures, and (f) concomitant medication. The prevalence of delayed reactions was lower than in previous large-scale studies. Significant risk factors included a history of allergy and performance of radiography during the pollinosis period, suggesting that allergy was involved in delayed adverse reactions. The type of radiographic procedure also had an influence.

Renal cyst pseudoenhancement with beam hardening effect on CT attenuation.

PURPOSE: The purpose of this study was to evaluate the extent of pseudoenhancement in a phantom model using three different CT scanners. METHODS: The phantom consisted of a water-filled balloon (cyst) suspended in varying concentrations of iodine solution, meant to simulate varying levels of renal enhancement. The phantom was scanned with single detector-row CT scanners of three different manufacturers. All scans were performed at 120 kV and 200 mA with 5 mm collimation. RESULTS: The degree of pseudoenhancement differed among the three scanners. In two of the scanners, the attenuation of water in the balloon (cyst) was noted to increase significantly as the iodine concentration in the cylinder was increased. However, the degree of pseudoenhancement was different between the two scanners. In the other scanner, attenuation of the cyst was noted to decrease as the iodine concentration in the cylinder decreased and to increase as the iodine concentration in the cylinder increased. CONCLUSION: The degree of pseudoenhancement may vary in scanners of different manufacturers. We may need to check the pattern and degree of pseudoenhancement in CT scanners before determining the enhancement threshold for simple renal cyst.

Significance of ST-segment morphology noted on electrocardiography during the recovery phase after exercise in patients with ischemic heart disease as analyzed with simultaneous dual-isotope single photon emission tomography.

BACKGROUND: The significance of differences in electrocardiographic morphology that occur during the recovery phase after exercise has not been clarified. We investigated the relationship between postexercise electrocardiographic morphology and the pattern of residual ischemia measured at that time. METHODS: Exercise dual-isotope single photon emission computed tomography was performed on 171 consecutive patients with chest pain syndrome. After injection of technetium-99m tetrofosmin at peak exercise and thallium-201 at 3 minutes after exercise, dual-isotope single photon emission computed tomographic images were obtained simultaneously. After cross-talk compensation, the extent of ischemia and its localization were measured at both peak exercise and after exercise. RESULTS: When 64 patients with angiographically and scintigraphically proven ischemic heart disease were grouped by morphology of ST-segment depressions at 3 minutes after exercise, 38 patients with the downsloping type had ischemia localized mainly to the middle and basal levels as compared with the more rapid resolution of ischemia in 12 patients with horizontal type and 14 patients with no ischemic electrocardiographic response (apical level 18.4% [7/38], 8.3% [1/12], and 0% [0/14], P = not significant, middle level 47.4% [18/38], 16.7% [2/12], and 7.1% [1/14], P <.01, basal level 57.9% [22/38], 33.3% [4/12], and 14.3% [2/14], P <.02, respectively) independent of the extent or localization of any ischemia noted during exercise (all levels, P = not significant). CONCLUSION: Electrocardiographic morphology during the recovery phase of exercise reflects the extent and localization of residual ischemia at that time independent of ischemic changes noted during exercise.