Wells, Michael

Background Detection of small renal calculi has benefitted from recent advances in computed tomography (CT) scanner design. Information regarding observer performance when using state-of-the-art CT scanners for this application is needed. Purpose To assess observer performance and the impact of radiation dose for detection and size measurement of <4 mm renal stones using CT with integrated circuit detectors and iterative reconstruction. Material and Methods Twenty-nine <4 mm calcium oxalate stones were randomly placed in 20 porcine kidneys in an anthropomorphic phantom. Four radiologists used a workstation to record each calculus detection and size. JAFROC Figure of Merit (FOM), sensitivity, false positive detections, and calculus size were calculated. Results Mean calculus size was 2.2 ± 0.7 mm. The CTDI vol values corresponding to the automatic exposure control settings of 160, 80, 40, 25, and 10 Quality Reference mAs (QRM) were 15.2, 7.9, 4.2, 2.7, and 1.3 mGy, respectively. JAFROC FOM was ≥ 0.97 at ≥ 80 QRM, ≥ 0.89 at ≥ 25 QRM, and was inferior to routine dose (160 QRM) at 10 QRM (0.72, P < 0.05). Per-calculus sensitivity remained ≥ 85% for every reader at ≥ 25 QRM. Mean total false positive detections per reader were ≤ 3 at ≥ 80 QRM, but increased substantially for two readers ( ≥ 12) at ≤ 40 QRM. Measured calculus size significantly decreased at ≤ 25 QRM ( P ≤ 0.01). Conclusion Using low dose renal CT with iterative reconstruction and ≥ 25 QRM results in high sensitivity, but false positive detections increase for some readers at very low dose levels (≤ 40 QRM). At very low doses with iterative reconstruction, measured calculus size will artifactually decrease.

ABSTRACTBACKGROUND AND PURPOSERequests for after‐hours emergent spine MR imaging seem to be increasing. We sought to review the trend in after hours spine MRI utilization at our institution and to determine how these results impacted therapeutic intervention.METHODSFollowing Institutional Review Board approval, reports from 179 after hours spinal MRI's performed over the past 13 years were obtained and the relevant electronic medical records were reviewed.RESULTSEmergent after hours spine MRI utilization increased from 7 per year to 23 over 13 years. Fifty‐eight percent (104/179) had significant findings. Twenty‐nine percent (52/179) of all patients imaged underwent surgery to treat pathologies identified on MR. Surgery was performed in only 2% (4/179) of these patients within 3 hours and 6% (10/179) within 6 hours of MRI completion. Five percent (8/179) had findings that were treated with radiation therapy and in 78% of these it was performed within 6–12 hours. Of those in whom steroids or antibiotics were initiated, 41% and 50% were treated within 3 hours of MR scanning, respectively.DISCUSSIONClinical use of emergent after hours spine MRI is steadily increasing at our institution. While MR imaging often discerned significant pathologies, performing these emergent studies rarely resulted in immediate surgical or radiotherapeutic intervention.