Emily Tam

CT Colonography and Computer-aided Detection: Effect of False-Positive Results on Reader Specificity and Reading Efficiency in a Low-Prevalence Screening Population

PURPOSE To retrospectively evaluate the effect of increasing numbers of computer-aided detection (CAD)-generated false-positive (FP) marks on reader specificity and reporting times by using computed tomographic (CT) colonography in a low-prevalence screening population. MATERIALS AND METHODS Ethics committee approval and informed consent were obtained for this HIPAA-compliant study. Four readers each read 48 data sets (26 men, 22 women; mean age, 57 years) from a screening population (three containing polyps) without CAD application, followed by review of the CAD output and recorded findings and diagnostic confidence. The 45 data sets that were designated as normal were chosen such that 22 generated 15 or fewer FP CAD marks and 23 generated more than 15 FP CAD marks. Sensitivity, specificity, and receiver operating characteristic (ROC) curves were calculated with and without CAD. The relationships between the number of CAD FP marks and reader confidence, reporting times, and correct data set classification were analyzed by using linear and logistic regression. RESULTS Across all readers, CAD resulted in four additional FP detections. Overall reader sensitivity and specificity (6-mm polyp threshold) before and after CAD application were 0.75 (95% confidence interval [CI]: 0.43, 0.95) versus 0.83 (95% CI: 0.52, 0.98) and 0.96 (95% CI: 0.91, 0.98) versus 0.93 (95% CI: 0.88, 0.96), respectively. The area under the ROC curve increased from 0.57 (95% CI: 0.34, 0.80) to 0.61 (95% CI: 0.42, 0.80). There was no correlation between an increasing number of CAD FP marks and reader confidence (P = .71) or correct study classification (P = .23), but there was a positive correlation with CAD-assisted reading times (0.06 [95% CI: 0.02, 0.10], P = .002). CONCLUSION Increasing numbers of CAD FP marks did not adversely influence correct reader study classification or diagnostic confidence, although reporting times did increase.

Diffusion tensor imaging of the anal canal at 3 tesla: Feasibility and reproducibility of anisotropy measures†

To assess the feasibility and reproducibility of 3‐tesla diffusion tensor imaging (DTI) of the anal canal.

Perfusion CT assessment of the colon and rectum : Feasibility of quantification of bowel wall perfusion and vascularization

The aim was to determine the feasibility of vascular quantification of the bowel wall for different anatomical segments of the colorectum. Following institutional ethical approval and informed consent, 39 patients with colorectal cancer underwent perfusion CT. Blood flow (BF), blood volume (BV), mean transit time (MTT), and permeability surface area product (PS) were assessed for different segments of the colorectum: ascending, transverse, descending colon, sigmoid, or rectum, that were distant from the tumor, and which were proven normal on contemporary colonoscopy, and subsequent imaging and clinical follow up. Mean (SD) for BF, BV, MTT and PS for the different anatomical colorectal segments were obtained and compared using a pooled t-test. Significance was at 5%. Assessment was not possible in 9 of 39 (23%) patients as the bowel wall was ≤ 5 mm precluding quantitative analysis. Forty-four segments were evaluated in the remaining 30 patients. Mean BF was higher in the proximal than distal colon: 24.0 versus 17.8 mL/min/100g tissue; p=0.009; BV, MTT and PS were not significantly different; BV: 3.46 versus 3.15 mL/100g tissue, p=0.45; MTT: 15.1 versus 18.3s; p=0.10; PS: 6.84 versus 8.97 mL/min/100 tissue, p=0.13, respectively. In conclusion, assessment of bowel wall perfusion may fail in 23% of patients. The colorectum demonstrates segmental differences in perfusion.

Mechanisms of hyoscine butylbromide to improve adenoma detection: A case-control study of surface visualization at simulated colonoscope withdrawal

Background and study aims: Antispasmodics may improve mucosal visualization during colonoscope withdrawal, potentially improving polyp and adenoma detection. Meta-analysis and case-control studies suggest a 9 % to 13 % relative increase in adenoma and polyp detection. We aimed to assess the impact of hyoscine butylbromide on the expected visualization during colonoscope withdrawal using a CT colonography (CTC) simulation. Patients and methods: Datasets from a previous CTC study examining the effect of antispasmodic were re-analyzed with customised CTC software, adjusted to simulate a standard colonoscopic view. Eighty-six patients received intravenous (IV) hyoscine butylbromide 20 mg, 40 mg or no antispasmodic. Main outcome measurements at unidirectional flythrough, simulating colonoscope withdrawal, were percentage colonic surface visualization, numbers and sizes of unseen areas, and colonic length. Results: Use of antispasmodic was associated with a significant relative increase in percentage surface visualization of 2.6 % to 3.9 %, compared with no antispasmodic, P < 0.006. Total numbers of missed areas and intermediate sized (300 – 1000 mm2) missed areas were significantly decreased, by approximately 20 %. There were no differences between the 20-mg and 40-mg doses. Mean colonic length (161 – 169 cm) was unchanged by antispasmodic. Conclusions: IV hyoscine butylbromide at simulated colonoscope withdrawal was associated with significant increases in surface visualization, which might explain up to half the improvement in adenoma detection seen in clinical studies.

Diffusion tensor imaging (DTI) of desmoid tumours in familial adenomatous polyposis: Initial experience

PURPOSE To assess the feasibility of diffusion tensor imaging (DTI) of desmoid tumours in familial adenomatous polyposis (FAP). MATERIALS AND METHODS Following ethical approval and informed consent, FAP patients with desmoids underwent DTI. Fractional anisotropy (FA), relative anisotropy (RA) and apparent diffusion coefficient (ADC) were compared to control muscle using Mann-Whitney test; and to tumour site and signal intensity using one way analysis of variance (ANOVA). Imaging was repeated after 1 year. RESULTS 15 desmoids (6 intra-abdominal; 6 abdominal wall, 3 extra-abdominal; size range: 1.6-22.9 cm) were evaluated in 9 patients. DTI was successful in 12/15 desmoid tumours. Median (range) of RA, FA and ADC were 0.23×10(-3) mm2/s (0.17-0.26); 0.27×10(-3) mm2/s (0.21-0.31); and 1.65×10(-3) mm2/s (1.39-1.91) for desmoids, significantly different from muscle: 0.27×10(-3) mm2/s (0.23-0.40), 0.32×10(-3) mm2/s (0.28-0.46), and 1.45×10(-3) mm2/s (0.92-1.63) (p=0.0001, p=0.0001, p=0.0016, respectively). There was no difference in RA, FA or ADC between tumour sites, or signal intensity (p>0.05). One year later, 2 patients had died. Tumour increased in size in 1 patient (+61%). DTI quantification was possible in only 8/13 tumours. FA, RA and ADC were not significantly different from baseline (p=0.77, 0.71 and 0.34, respectively). CONCLUSIONS Assessment of water diffusion has the potential to provide insight into tumour microstructure and is feasible in desmoids. Desmoid tumours demonstrate anisotropy but diffusion is less restricted and less directional than in muscle.