Richard Tello

Spiral CT evaluation of coronary artery bypass graft patency

Spiral CT (SCT) differs from conventional CT in that the entire heart can be rapidly imaged in the axial plane following the peripheral infusion of small quantities of contrast material. As contrast material travels through coronary artery bypass graft segments, good image detail is achieved, allowing visualization of entire coronary artery graft segments during a single injection. The patency of 43 coronary artery bypass grafts in 14 patients on contrast enhanced SCT, with timing tailored to patient-specific transit times, was compared with that obtained by selective graft angiography. With use of 5 or 8 mm/s table feed and 24 s volumetric acquisitions, SCT established graft patency with 85.7% sensitivity and 100% specificity compared to angiographic examination (96.4% sensitivity and 100% specificity). The mean time between angiography and SCT was 2.1 days, with 86% of SCT studies done within 24 h after angiography. The utilization of dynamic scanning to establish the patient-specific time delay prior to initiation of SCT proved crucial in improving the quality and reliability of SCT bypass graft patency assessment. The paired McNemar test indicates no significant difference between angiography and SCT in establishing patency rates.

Signal characteristics of focal liver lesions on double echo T2-weighted conventional spin echo MRI: observer performance versus quantitative measurements of T2 relaxation times.

PURPOSE The purpose of this work was to evaluate the ability of expert readers to differentiate benign from malignant liver lesions based on visual assessment of lesion signal intensity on double echo T2-weighted conventional spin echo (CSE) MR images and to compare reader performance with quantitative measurements of T2 relaxation times. METHOD Sixty-seven MR examinations demonstrating 85 liver lesions (37 hemangiomas, 32 malignancies, 15 cysts, and 1 focal nodular hyperplasia) on double echo T2-weighted CSE sequences (TR 3,600 ms/TE 50, 160 ms) were qualitatively reviewed by three independent readers. T2 relaxation times were calculated for each lesion. Receiver operating characteristic (ROC) analyses of expert readers were compared with calculated T2 relaxation times. RESULTS T2 values performed significantly better than subjective reader analysis for liver lesion characterization (area under ROC = 0.93 vs. 0.81, 0.78, and 0.75; p < 0.0001). With use of a T2 threshold of 125 ms, the sensitivity of T2 values for malignant lesions was 100%, specificity 71%, and accuracy 84%. By comparison, the sensitivity of the three readers for malignant lesions was 76-83%, with a specificity of 61-72% and an overall accuracy of 71-80%. CONCLUSION Despite expert reader analyses, subjective evaluations of liver lesion signal characteristics are prone to inaccuracy and lack certainty and consistency when intermediate TEs (50/160 ms) are used. Quantitative measurements of T2 relaxation times should be performed to accurately and confidently differentiate benign from malignant liver lesions. Use of a higher T2 threshold than previously recommended is required to avoid misclassification of malignancies.

Observer performance in assessing anemia on thoracic CT.

OBJECTIVE The purpose of this study was to evaluate the ability of expert reviewers to differentiate an anemic from a nonanemic state on the basis of visual assessment of the relative attenuation of blood in the left ventricle on noncontrast thoracic CT images and to compare reviewer performance with quantitative measurement of CT density in Hounsfield units. MATERIALS AND METHODS One hundred two noncontrast thoracic CT examinations were qualitatively reviewed by three independent reviewers. Hounsfield unit measurements of the blood in the left ventricle were recorded by a fourth individual. Anemia was defined as a hemoglobin level of less than 10 g/dL. Receiver operating characteristic (ROC) analyses of expert reviewers were compared with measured Hounsfield units. RESULTS Hounsfield unit measurements performed significantly better than subjective reviewer analyses for differentiation of an anemic from a nonanemic state (area under ROC curve = 0.85 vs 0.72, 0.70, and 0.69; 95% confidence interval, 0.78-0.92 vs 0.63-0.81, 0.61-0.79, and 0.60-0.78, respectively; p < 0.05). With use of a CT density threshold of 35 H, the sensitivity for anemia was 76% and specificity was 81%, whereas the sensitivity of three reviewers was 40-72% with a specificity of 60-83%. Interobserver agreement was found to be poor by kappa statistic (0.0906-0.2128). The correlation coefficient for the analysis of Hounsfield unit versus hemoglobin level was 0.72. Separating data by patient sex revealed a correlation coefficient of 0.81 for men versus 0.52 for women, although the actual regression lines were not statistically different (p > 0.05). CONCLUSION Despite expert reviewer analyses, subjective evaluations of blood attenuation characteristics are prone to inaccuracy and show poor interobserver agreement. Quantitative measurements of CT density in Hounsfield units should be performed to accurately differentiate an anemic from a nonanemic state when serum hemoglobin levels are not readily available.

World Wide Web program for optimizing and assessing medical student performance during the radiology clerkship.

RATIONALE AND OBJECTIVES The purpose of this study was to adapt the technology of the World Wide Web to the teaching and evaluation of medical students participating in the radiology clerkship at our institution. MATERIALS AND METHODS Teaching modules were placed on a local intranet site. One hundred two student evaluations were conducted online as a standardized, written- and image-based test that was administered both before and after the clerkship. The computer-delivered test consisted of 40 standardized questions that were sorted by category (based on American College of Radiology code criteria) and randomly administered from a pool of 200 potential questions. Scores from before and after the clerkship were analyzed statistically to evaluate the effectiveness of the educational program and the student performance. Student case presentation scoring and clerkship administration tasks were also evaluated both before and after implementation of the modules during the first 12 months of this project (July 1997 to July 1998). RESULTS A statistically significant (P < .001) improvement in test performance was found in 102 consecutive students, and all 102 students (100%) preferred the digital-testing format. The amount of time needed to tabulate the teacher evaluation, grade the test, and score the oral presentations decreased substantially with the digital system. CONCLUSION An intranet-based method of evaluating students in an ongoing fashion allows for additional growth in content and ease of use during the radiology clerkship.

DYNAMIC GADOLINIUM DTPA-ENHANCED MAGNETIC RESONANCE OF INTRAVASCULAR STENTS

RATIONALE AND OBJECTIVES Magnetic resonance contrast enhancement depends on the timing of image acquisition. Human trials have demonstrated efficacy of renal artery stents on salvage of renal function. This study assessed the ability of dynamic gadolinium (Gd)-DTPA administration to demonstrate renal and iliac artery stent patency compared to conventional angiography as the gold standard. METHODS Seven subjects with eight stents referred for angiography underwent dynamic magnetic resonance studies, all with renal artery stenting. All were examined with conventional angiography and after dynamic Gd-DTPA infusion. Coronal magnetic resonance images were acquired using a GE Signa 1.5 T magnet (fast spoiled gradient echo; echo time = 4.2 ms; repetition time = 68-150 ms; flip angle = 75 degrees) 0 to 600 seconds after 0.1 mmol/Kg Gd-DTPA intravenous bolus injection during sequential breath-hold acquisitions 13 to 32 seconds each. RESULTS All eight stents were visualized with 100% accurate patency documentation. CONCLUSIONS Fast spoiled gradient echo magnetic resonance imaging with bolus Gd-DTPA administration can provide adequate time and spatial resolution to demonstrate arterial stent patency.

Value of spiral CT in hemodynamically stable patients following blunt chest trauma

INTRODUCTION Features of spiral CT (SCT)-fast scanning, dynamic injection of contrast allowing optimal vessel opacification, and supplemental multiplanar imaging-promises to provide increased accuracy in the diagnosis of acute and non acute thoracic vascular disease. Recent work demonstrating the cost effective triage of hemodynamically stable patients after blunt chest trauma for angiography based on dynamic CT findings has prompted an investigation into the accuracy of SCT in this clinical setting. METHODS A retrospective review of all patients seen in the emergency department over the period of one year for aortic, thoracic, or blunt chest trauma evaluation was performed (74 patients) and all SCT scans available were reviewed and data reformatted for optimal delineation of pathology using maximum intensity projection and multiplanar reformation. The accuracy and predictive positive and negative values of SCT were calculated with respect to angiography, surgical, and/or clinical follow up evaluation. RESULTS Twenty three (31%) patients went directly to angiography owing to mediastinal widening on chest film and hemodynamic instability, of which four were positive and required emergent surgery. Seven hemodynamically stable patients (9%) had noncontrast SCT owing to mediastinal widening on chest film, all of which had angiography with none having great vessel trauma. Fourty four hemodynamically stable patients (60%) had contrast enhanced SCT (ceSCT), of which five (11%) were abnormal and underwent angiography, four of these were positive for aortic damage, one for a subclavian artery laceration. Of the remaining 39 patients who had normal ceSCT; five had angiography, all of which were normal. Of the remaining 34 patients that had normal ceSCT none had adverse outcome on clinical follow-up, minimum of 12 months. CONCLUSION The predictive positive value for aortic trauma of ceSCT in blunt trauma is 80%, with a predictive negative value of 100%, indicating that it is feasible for SCT to be a first line exam in blunt chest trauma in the future.

A web based video tool for MR arthrography

OBJECTIVE Our objective was to integrate digital video and web technology to construct a useful self paced learning tool to deliver recorded techniques of magnetic resonance (MR) arthrography for junior radiology residents and medical students. CONCLUSION The streaming of audio media, an emerging technology, is an effective vehicle to deliver educational material over the Internet using commercially available PCs and modems, especially when teaching resources are limited.

MR hysterography using axial long TR imaging with three-dimensional projections of the uterus

A rapid screening technique for the presentation of uterine cavity anatomy obtained with MR is described. MR hysterographic (MRHG) images were generated and evaluated for uterine cavity abnormalities. Six patients referred for MRI evaluation of the uterus for infertility had an MRI using a pelvic phased array coil with axial 3 mm interleaved fast spin echo images (TR 9000 ms, TE 288 ms with fat saturation) processed using maximum intensity projection algorithms to construct MRHG images. Using the conventional MR sequence as the gold standard the MRHG images were evaluated by two reviewers and accuracy calculated. MRHG took less than 3 min, demonstrated the correct diagnosis in all with a quality score of diagnostic to optimal, and with excellent interobserver agreement (kappa 0.9).

Incidence of adrenal masses in patients referred for renal artery stenosis screening MR.

Tello R, Chaoui A, Fenlon H, et al. Incidence of adrenal masses in patients referred for renal artery stenosis screening MR. Invest Radiol 2001;36:518–520. rationale and objectives. Prior work has shown the efficacy of magnetic resonance (MR) in renal artery stenosis evaluation. The increasing role of renal artery stenosis in the differential diagnostic evaluation of hypertension raises the question of whether MR should be used as a screening modality. This project evaluated the additional potential benefits of MR by determining the incidence of adrenal masses in this selected population. methods.A 2-year retrospective study analysis of patients who failed to respond to antihypertensive medical management and were referred for renal MR for hypertension amassed 77 subjects ranging in age from 18 to 88 years. A masked analysis for adrenal masses was performed on this data set. Magnetic resonance techniques included T2-weighted turbo spin-echo (repetition time [TR] 2000–4000 ms, echo time [TE] 80–100 ms, turbo factor 2–16), T1-weighted spin-echo (TR 200–500 ms, TE 10–30 ms), gradient-echo time-of-flight (TR 26 ms, TE 6.9 ms, 40° flip angle, 2 excitations), and dynamic gadopentetate dimeglumine–enhanced MR angiography (three-dimensional gradient recalled echo, TR 10 ms, TE 3 ms, 40° flip angle, 1 excitation). results.Thirty-three patients had renal artery disease, 44 had normal renal arteries, and 7 had adrenal masses. Forty-three percent of patients who underwent renal MR had disease of the renal arteries detected, and 9% of patients referred for MR had adrenal masses that would have been missed with scintigraphy and/or angiography, of which 57% were responsible for hypertension. conclusions.The ability to evaluate renal artery and adrenal anatomy globally can be useful, as exemplified in the current series, and the adrenals should be examined carefully in any renal MR in a hypertensive patient.

In vivo three-dimensional evaluation of the tracheobronchial tree.

Traditionally computed axial tomography has had limitations in evaluating diseases that affect the tracheobronchial tree because of respiratory-induced artifacts, with the likelihood of missing lesions as a result of misregistration. Spiral computed tomography (CT) differs from conventional CT in that the entire thorax can be rapidly imaged in the axial plane after a single breath-hold. Five patients underwent non-contrast-enhanced volumetric CT, with emphasis on three-dimensional reconstruction, and endoscopic evaluation with pathologic confirmation. In all cases, there was complete corroboration between volumetric CT and endoscopic evaluation. The use of selective thresholds allowed the air within the tracheobronchial tree to be used as a negative contrast agent. Thus with the integration of selective windowing, detailed three-dimensional tracheobronchial anatomy may be elucidated. The absence of respiratory registration artifact due to the single breath-hold technique raises the confidence that three-dimensional and multiplanar images generated from such studies are accurate representations of the pathologic conditions at hand. By the integration of volumetric CT techniques and rapid three-dimensional display of tracheobronchial structures, volumetric CT bronchography becomes practical.