Impact of model-based iterative reconstruction on low-contrast lesion detection and image quality in abdominal CT: a 12-reader-based comparative phantom study with filtered back projection at different tube voltages.

OBJECTIVES: To evaluate the impact of model-based iterative reconstruction (MBIR) on image quality and low-contrast lesion detection compared with filtered back projection (FBP) in abdominal computed tomography (CT) of simulated medium and large patients at different tube voltages. METHODS: A phantom with 45 hypoattenuating lesions was placed in two water containers and scanned at 70, 80, 100, and 120 kVp. The 120-kVp protocol served as reference, and the volume CT dose index (CTDIvol) was kept constant for all protocols. The datasets were reconstructed with MBIR and FBP. Image noise and contrast-to-noise-ratio (CNR) were assessed. Low-contrast lesion detectability was evaluated by 12 radiologists. RESULTS: MBIR decreased the image noise by 24% and 27%, and increased the CNR by 30% and 29% for the medium and large phantoms, respectively. Lower tube voltages increased the CNR by 58%, 46%, and 16% at 70, 80, and 100 kVp, respectively, compared with 120 kVp in the medium phantom and by 9%, 18% and 12% in the large phantom. No significant difference in lesion detection rate was observed (medium: 79-82%; large: 57-65%; P > 0.37). CONCLUSIONS: Although MBIR improved quantitative image quality compared with FBP, it did not result in increased low-contrast lesion detection in abdominal CT at different tube voltages in simulated medium and large patients. KEY POINTS: • MBIR improved quantitative image quality but not lesion detection compared with FBP. • Increased CNR by low tube voltages did not improve lesion detection. • Changes in image noise and CNR do not directly influence diagnostic accuracy.

Organ-based tube current modulation in a clinical context: Dose reduction may be largely overestimated in breast tissue.

OBJECTIVES: Organ-based tube current modulation aims to reduce exposure to radiosensitive organs like the breasts by considering their anatomical location and altering tube current during rotation. Former phantom studies demonstrated a dose reduction of 20-37 %. Our study aimed to estimate the potential of dose reduction with this technique in relation to the actual location of breast tissue in a large clinical cohort. METHODS: A 1-year cohort of chest CTs of females (N=1,263) was retrospectively evaluated. To estimate the relative dose effect, breast location was analysed by measuring the angle range of glandular tissue within the different dose zones. Relative exposure compared with constant tube current was calculated. Descriptive statistics and Wilcoxon-test were applied. RESULTS: Only 63 % of angle range of glandular breast tissue was found inside the reduced dose zone. The estimated mean relative dose reduction was lower than observed in former phantom studies(16 % vs. 20-37 %) but still significant compared to constant tube current (p<0.0001). CONCLUSIONS: Although organ-based tube current modulation results in a significant reduction of breast exposure compared to non-modulated irradiation, the technique cannot unfold its full potential, because breast tissue is often located outside the reduced dose zone, resulting in significantly lower dose reduction than expected. KEY POINTS: • OBTCM results in significant dose reduction compared to constant tube current scans. • A substantial portion of glandular tissue lies outside the reduced dose zone. • Potential dose reduction using organ-based tube current modulation may be overestimated.

An unexpected cause for cavitary pneumonia and empyema.

Tularemia is an emerging zoonotic disease mainly of the Northern Hemisphere caused by the Gram-negative coccobacillus Francisella tularensis. It is affecting a wide range of animals and causes human disease after insect and tick bites, skin contact, ingestion and inhalation. A 66-year-old man presented to our clinic with cavitary pneumonia and distinct pleural effusion. After failure of empiric antibiotic therapy, thoracoscopic assisted decortication and partial excision of the middle lobe were conducted. Conventional culture methods and broad-range bacterial PCR including RipSeqMixed analysis were performed from the excised biopsies. Culture results remained negative but broad-range PCR targeting the first half of the 16S rRNA gene revealed F. tularensis DNA. This result was confirmed by F. tularensis-specific PCR and by serology. The source of infection could not be explored. To conclude, we report the rare clinical picture of a community-acquired pneumonia followed by pleural effusion and empyema due to F. tularensis. Broad range bacterial PCR proved to be a powerful diagnostic tool to detect the etiologic organism.

Variability of MRI Aortic Stiffness Measurements in a Multicenter Clinical Trial Setting: Intraobserver, Interobserver, and Intracenter Variability of Pulse Wave Velocity and Aortic Strain Measurement.

PURPOSE: To assess intraobserver, interobserver, and scan-rescan variability of MRI aortic stiffness measurements in a multicenter trial setting. MATERIALS AND METHODS: This study was a retrospective analysis of prospectively collected data in a multicenter prospective clinical trial (clinicaltrials.gov ID NCT01870739). Forty-five adult patients (31 men; mean age, 58 years ± 12 [standard deviation]; 15 patients per center; three centers) with arterial hypertension underwent standardized 3-T baseline MRI assessments between June and September 2014. Aortic strain was calculated from maximum and minimum aortic area measurements repeated three times by three readers at three aortic levels on three retrospectively gated axial gradient-echo (GRE) data sets. Pulse wave velocity (PWV) was assessed three times by five readers as Δx/Δt: Δx was measured on a parasagittal GRE image of the aortic arch, and Δt was extracted from ascending and descending aortic velocity curves created on three axial phase-contrast acquisitions. Intraobserver, interobserver, and scan-rescan variability was calculated using percentage coefficient of variation (COV). RESULTS: Aortic strain variability was lowest at the level of the distal descending aorta (DDA) with median COVs of 1.6% for intraobserver variability, 4.0% for interobserver variability, and 10.3% for scan-rescan variability. It was highest at the ascending aorta (AA) with COVs of 3.6% for intraobserver variability, 10.7% for interobserver variability, and 19.8% for scan-rescan variability. Variability of PWV was low: 0.7% for intraobserver variability, 1.5% for interobserver variability, and 8.1% for scan-rescan variability. CONCLUSION: Low variability can be achieved for aortic strain and PWV measurements in a multicenter trial setting using standardized MRI protocols. Although COV was lower when measuring aortic strain at DDA compared with AA, variability was acceptable at both anatomic locations.Supplemental material is available for this article.© RSNA, 2020.

Stress cardiac MR imaging: the role of stress functional assessment and perfusion imaging in the evaluation of ischemic heart disease.

Stress cardiac magnetic resonance imaging can provide valuable information for the diagnosis and management of ischemic heart disease (IHD). It plays an important role in the initial diagnosis in patients with acute chest pain, in the diagnosis of complications post myocardial infarction (MI), in the assessment of the right ventricle after an acute MI, to detect complications due to or after interventions, in prediction of myocardial recovery, to detect inducible ischemia in patients with known IHD, in differentiating ischemic from non-ischemic dilated cardiomyopathy, and in risk stratification.

Potential Benefits of Prophylactic Cholecystectomy in Patients Undergoing Bariatric Bypass Surgery.

BACKGROUND: In patients with morbid obesity, laparoscopic Roux-en-Y gastric bypass (LRYGB) is the treatment of choice. Patients with gallstones routinely undergo cholecystectomy at the same time as LRYGB. Although the risk of developing gallstones afterwards is high, prophylactic cholecystectomy during LRYGB remains controversial. Therefore, we conducted a retrospective study to evaluate the risk associated with prophylactic cholecystectomy and risk factors for developing gallstones after LRYGB. METHODS: Data for patients on whom we consecutively performed LRYGB in 2003-2008 were extracted from the prospective bariatric database. The primary endpoint of the study was detection of newly developed gallstones by ultrasonography, and the secondary endpoint was evaluation of the incidence of post-LRYGB cholecystectomy (questionnaire). RESULTS: Of 117 patients who underwent LRYGB, 20 (17 %) had a previous and 26 (22 %) had a concomitant cholecystectomy. Of the 71 LRYGB patients remaining who had not had their gallbladders removed, 22 (34 %) developed gallstones, with 11 (17 %) requiring emergency cholecystectomy before the study began. Seven (10 %) patients were lost to follow-up, and 53 (75 %) underwent abdominal ultrasound during follow-up, which detected stones in another 11 (17 %) patients up to end of the study period. CONCLUSIONS: Nearly 50 % of our patients had either experienced gallstones before LRYGB or developed gallstones after LRYGB. In the group with new gallstone development, 50 % required emergency cholecystectomy. These results, together with the reported better quality of life after a combined procedure and the reported economic benefits, support the use of concomitant prophylactic cholecystectomy in patients undergoing LRYGB.