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doi: 10.1148/radiol.2303030297pmid: 14990827
Small increments in the complexity of clinical studies can readily take sample size estimation and statistical power analysis beyond the capabilities of simple mathematic formulas. In this article, the method of simulation is presented as a general technique with which sample size may be calculated for complex study designs. Applications of simulation for determining sample size requirements in studies involving correlated data and comparisons of receiver operating characteristic curves are discussed.
Kalra, Mannudeep K.; Maher, Michael M.; Toth, Thomas L.; Hamberg, Leena M.; Blake, Michael A.; Shepard, Jo-Anne; Saini, Sanjay
doi: 10.1148/radiol.2303021726pmid: 14739312
Recent technologic advances have markedly enhanced the clinical applications of computed tomography (CT). While the benefits of CT exceed the harmful effects of radiation exposure in patients, increasing radiation doses to the population have raised a compelling case for reduction of radiation exposure from CT. Strategies for radiation dose reduction are difficult to devise, however, because of a lack of guidelines regarding CT examination and scanning techniques. Various methods and strategies based on individual patient attributes and CT technology have been explored for dose optimization. It is the purpose of this review article to outline basic principles of CT radiation exposure and emphasize the need for CT radiation dose optimization based on modification of scanning parameters and application of recent technologic innovations.
Macari, Michael; Bini, Edmund J.; Jacobs, Stacy L.; Naik, Sanjay; Lui, Yvonne W.; Milano, Andrew; Rajapaksa, Roshini; Megibow, Alec J.; Babb, James
doi: 10.1148/radiol.2303021624pmid: 14739311
PURPOSE: To compare thin-section multi–detector row computed tomographic (CT) colonography with conventional colonoscopy in the evaluation of colorectal polyps and cancer in asymptomatic average-risk patients. MATERIALS AND METHODS: Sixty-eight asymptomatic men (age > 50 years) scheduled to undergo screening colonoscopy were enrolled in this study. CT colonography was followed by conventional colonoscopy, performed on the same day. Supine and prone CT colonography were performed after colonic insufflation with room air. A gastroenterologist measured all polyps, which were categorized as 1–5, 6–9, or over 10 mm. Biopsy and histologic evaluation were performed of all polyps. CT colonography and colonoscopy results were compared for location, size, and morphology of detected lesions. Point estimates and 95% CIs were provided for specificity and sensitivity of CT by using results at conventional colonoscopy as the reference standard. RESULTS: At colonoscopy, 98 polyps were identified in 39 patients; 21 (21.4%) of 98 were detected at CT colonography. Sensitivity was 11.5% (nine of 78) for polyps 1–5 mm, 52.9% (nine of 17) for polyps 6–9 mm, and 100% (three of three) for polyps over 10 mm. Results at colonoscopy were normal in 29 (42.6%) of 68 patients; at CT colonography, results were correctly identified as normal in 26 of these 29 patients. In one of these patients, a lesion larger than 10 mm was detected at CT colonography. The per-patient specificity of CT was 89.7% (26 of 29; 95% CI: 72.7%, 97.8%). The mean time for CT image interpretation was 9 minutes. CONCLUSION: In patients at average risk for colorectal cancer, CT colonography is a sensitive and specific screening test for detecting polyps 10 mm or larger; the sensitivity for detecting smaller polyps is decreased. Examination findings can be interpreted in a clinically feasible amount of time.
Hussain, Hero K.; Syed, Ibrahim; Nghiem, Hanh V.; Johnson, Timothy D.; Carlos, Ruth C.; Weadock, William J.; Francis, Isaac R.
doi: 10.1148/radiol.2303020921pmid: 14739306
PURPOSE: To assess if T2-weighted magnetic resonance (MR) imaging provides added diagnostic value in combination with dynamic gadolinium-enhanced MR imaging in the detection and characterization of nodular lesions in cirrhotic liver. MATERIALS AND METHODS: Two readers retrospectively and independently analyzed 54 MR imaging studies in 52 patients with cirrhosis. In session 1, readers reviewed T1-weighted and dynamic gadolinium-enhanced images. In session 2, readers reviewed T1-weighted, dynamic gadolinium-enhanced, and respiratory-triggered T2-weighted fast spin-echo images. Readers identified and characterized all focal lesions by using a scale of 1–4 (1, definitely benign; 4, definitely malignant). Multireader correlated receiver operating characteristic (ROC) analysis was employed to assess radiologist performance in session 2 compared with session 1. The difference in the areas under the ROC curves for the two sessions was tested. In a third session, readers assessed conspicuity of biopsy-proved lesions on T2-weighted MR images by using a scale of 1–3 (1, not seen; 3, well seen) and identified causes of reduced conspicuity. RESULTS: Two additional benign lesions were detected by each reader in session 2. Fifty-five lesions had pathologic verification, including 32 malignant, three high-grade dysplastic, and 20 benign nodules. There was no significant difference in the area under the ROC curves between the two sessions ( P = .48). Thirty-two lesions were inconspicuous on T2-weighted MR images because of parenchymal heterogeneity, breathing artifacts (particularly in patients with ascites), and lesion isointensity with liver parenchyma. T2-weighted MR imaging was useful in the evaluation of cysts and lymph nodes. CONCLUSION: T2-weighted MR imaging does not provide added diagnostic value in the detection and characterization of focal lesions in cirrhotic liver.
Yeh, Benjamin M.; Breiman, Richard S.; Taouli, Bachir; Qayyum, Aliya; Roberts, John P.; Coakley, Fergus V.
doi: 10.1148/radiol.2303021775pmid: 14990830
PURPOSE: To compare biliary tract depiction in living potential liver donors at conventional magnetic resonance (MR), mangafodipir trisodium–enhanced excretory MR, and multi–detector row computed tomographic (CT) cholangiography. MATERIALS AND METHODS: Eight living potential liver donors underwent iodipamide meglumine–enhanced CT cholangiography. Eight different potential liver donors then underwent conventional MR cholangiography and mangafodipir trisodium–enhanced excretory MR cholangiography. Two readers independently scored all first-, second-, and third-order biliary branches with a four-point scale from 0 (not seen) to 3 (excellent visualization). Interobserver agreement was calculated by using the weighted κ statistic. Scores were compared between imaging modalities by using generalized estimating equations. Imaging findings of second-order biliary tract anatomy were compared with intraoperative findings for nine patients. RESULTS: Interobserver agreement for overall biliary tract visualization was good for CT, conventional MR, and excretory MR cholangiography (with weighted κ values of 0.76, 0.66, and 0.79, respectively). The mean second-order biliary branch visualization scores for readers 1 and 2, respectively, were significantly higher at CT cholangiography (2.81 and 2.75) than at conventional MR (1.84 and 1.75, P < .001), excretory MR (2.00 and 2.06, P < .001), and combined conventional and excretory MR cholangiography (2.31 and 2.25, P < .01). At CT, conventional MR, and excretory MR cholangiography, respectively, second-order biliary branching anatomy was discernible in eight, five, and seven patients, with second-order biliary branch variants seen in three, two, and two patients. Surgical findings confirmed the pattern of second-order biliary branching seen at CT in five patients, that seen at conventional MR imaging in one patient, and that seen at excretory MR cholangiography in three patients. At surgery, one case of variant biliary anatomy was found to have been missed at CT cholangiography. CONCLUSION: In living potential liver donors, CT cholangiography enables significantly better biliary tract visualization than conventional or excretory MR cholangiography either alone or in combination.
de Bazelaire, Cedric M. J.; Duhamel, Guillaume D.; Rofsky, Neil M.; Alsop, David C.
doi: 10.1148/radiol.2303021331pmid: 14990831
PURPOSE: To measure T1 and T2 relaxation times of normal human abdominal and pelvic tissues and lumbar vertebral bone marrow at 3.0 T. MATERIALS AND METHODS: Relaxation time was measured in six healthy volunteers with an inversion-recovery method and different inversion times and a multiple spin-echo (SE) technique with different echo times to measure T1 and T2, respectively. Six images were acquired during one breath hold with a half-Fourier acquisition single-shot fast SE sequence. Signal intensities in regions of interest were fit to theoretical curves. Measurements were performed at 1.5 and 3.0 T. Relaxation times at 1.5 T were compared with those reported in the literature by using a one-sample t test. Differences in mean relaxation time between 1.5 and 3.0 T were analyzed with a two-sample paired t test. RESULTS: Relaxation times (mean ± SD) at 3.0 T are reported for kidney cortex (T1, 1,142 msec ± 154; T2, 76 msec ± 7), kidney medulla (T1, 1,545 msec ± 142; T2, 81 msec ± 8), liver (T1, 809 msec ± 71; T2, 34 msec ± 4), spleen (T1, 1,328 msec ± 31; T2, 61 msec ± 9), pancreas (T1, 725 msec ± 71; T2, 43 msec ± 7), paravertebral muscle (T1, 898 msec ± 33; T2, 29 msec ± 4), bone marrow in L4 vertebra (T1, 586 msec ± 73; T2, 49 msec ± 4), subcutaneous fat (T1, 382 msec ± 13; T2, 68 msec ± 4), prostate (T1, 1,597 msec ± 42; T2, 74 msec ± 9), myometrium (T1, 1,514 msec ± 156; T2, 79 msec ± 10), endometrium (T1, 1,453 msec ± 123; T2, 59 msec ± 1), and cervix (T1, 1,616 msec ± 61; T2, 83 msec ± 7). On average, T1 relaxation times were 21% longer ( P < .05) for kidney cortex, liver, and spleen and T2 relaxation times were 8% shorter ( P < .05) for liver, spleen, and fat at 3.0 T; however, the fractional change in T1 and T2 relaxation times varied greatly with the organ. At 1.5 T, no significant differences ( P > .05) in T1 relaxation time between the results of this study and the results of other studies for liver, kidney, spleen, and muscle tissue were found. CONCLUSION: T1 relaxation times are generally higher and T2 relaxation times are generally lower at 3.0 T than at 1.5 T, but the magnitude of change varies greatly in different tissues.
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