Resident interpretation of emergency CT scans in the evaluation of acute appendicitis.

PURPOSE: Radiology resident interpretation of computed tomographic (CT) scans at academic institutions often guides management of cases of suspected acute appendicitis in the emergency department. The purpose of this study was to compare resident and faculty interpretation of CT scans obtained for acute appendicitis. MATERIALS AND METHODS: From December 16, 1999, to July 13, 2000, CT was performed in 103 consecutive patients between the hours of 9:00 PM and 8:00 AM who were suspected of having acute appendicitis. The authors compared the residents' preliminary written interpretations with both the final reports written by the faculty and the surgical findings. The faculty interpreting the CT scans were aware of resident interpretations but were not aware that a study was being conducted. RESULTS: The final faculty interpretation and the preliminary resident interpretation were identical in 96 of the 103 patients (93%; 95% confidence interval: 87.8%, 97.2%). In only one patient was a scan originally interpreted as negative interpreted as positive by the faculty member. Clinically, the patient did not have acute appendicitis, and surgery was not perforrmed. CONCLUSION: In the diagnosis of acute appendicitis, image interpretations made by adequately trained radiology residents can be expected to closely match those of the radiology faculty, and the practice of after-hours interpretation of such studies by radiology residents is safe.

MRA for diagnosis of venous thromboembolism.

Direct imaging of pulmonary embolism (PE) and deep vein thrombosis (DVT) with CT, and potentially with MR, will continue to replace V/Q scintigraphy. Venous imaging with MR far detecting DVT is used in a few centers, and their published accuracy figures are impressive. Recent studies of MR pulmonary angiography for PE reported that sensitivity of MRA was 85-100%, specificity 95-96%, but this data must be confirmed in other centers and patient populations. MR has advantages compared with CT, which make it worthwhile to continue MR development. Ionizing radiation and iodinated contrast material are not used. Imaging the pulmonary arteries and then imaging whichever venous region is of clinical interest is practical in a single examination. Repeated examinations can be performed safely. New contrast materials will facilitate the practicality and accuracy of the MR technique and perfusion imaging may increase sensitivity. MR also has disadvantages compared with CT. It does not image effectively the non-vascular compartment of the lungs. It is more expensive, patient monitoring is more cumbersome, and a routine technique, which embodies all of MR's potential advantages, has not been packaged and tested. Accordingly, helical CT is a realistic option in clinical management of patients with suspected PE in most centers, while clinical application of MR is limited to centers with appropriate MR expertise and technology. However, MR has a number of fundamental characteristics that make it a potentially ideal modality for evaluating patients with suspected acute venous thromboembolic disease and further clinical research with MRA is warranted.

Deep venous thrombosis: detection by using indirect CT venography. The Pulmonary Angiography-Indirect CT Venography Cooperative Group.

PURPOSE: To assess the clinical benefits of performing indirect computed tomographic (CT) venography after pulmonary CT angiography to detect deep venous thrombosis (DVT) in patients suspected of having a pulmonary embolism. MATERIALS AND METHODS: The authors prospectively enrolled 541 consecutive patients who underwent pulmonary CT angiography for suspected pulmonary embolism at seven institutions. Using a protocol that optimizes venous enhancement without additional contrast material injection, the authors obtained contiguous images from the pelvis to the popliteal fossa. Ultrasonography (US) also was performed in 116 patients. RESULTS: DVT was found at indirect CT venography in 45 (8%), and pulmonary embolism was found at pulmonary CT angiography in 91 (17%) of 541 patients. Among the 45 patients with DVT, DVT occurred in 16 patients who had no pulmonary embolism at pulmonary CT angiography, which increased the diagnosis of thromboembolic disease by 18%. Among 116 patients who underwent US and indirect CT venography, 15 had DVT at US, and in all 15, DVT also was seen at indirect CT venography. In four additional cases, DVT was seen at only indirect CT venography. CONCLUSION: Among patients suspected to have pulmonary embolism, a substantial number had DVT in the absence of pulmonary embolism. Combined pulmonary CT angiography-indirect CT venography can depict these cases with accuracy comparable to that of US and thus could have a significant effect on patient care.

Pitfalls in myocardial perfusion assessment with dynamic MR imaging after administration of a contrast material bolus in dogs.

RATIONALE AND OBJECTIVES: The authors evaluated the artifacts observed on myocardial perfusion curves derived from an inversion-prepared fast gradient-echo (GRE) imaging sequence in dogs after injection of a gadolinium-based contrast agent. MATERIALS AND METHODS: Six mongrel dogs were divided into three groups. In groups 1 and 2, anesthesia was maintained with pentobarbital. Group 2 also received an intravenous injection of atropine (0.03 mg/kg). In group 3, anesthesia was maintained with isoflurane (1.0%). Imaging was performed on a 1.5-T magnetic resonance (MR) imaging unit (one section per heart beat, a 30 x 15-cm field of view, 10-mm section thickness, and 64-kHz bandwidth). Region-of-interest (ROI) markers were placed on the blood pool of the left intraventricular cavity, anterior wall of the left ventricle, and anterior to the chest wall to track respiratory motion. RESULTS: In group 1, the signal intensity (SI) periodically increased during each inspiration due to respiratory sinus arrhythmia. The relation between the SI increase and the variation of the delay between images was demonstrated in vitro and by computer simulations. No periodic increase of the SI was observed when regular cardiac rhythm was maintained by pharmacologic inhibition of the vagal-mediated chronotropic response with either the addition of atropine to pentobarbital or the use of isoflurane as the anesthetic agent. CONCLUSION: In an inversion-prepared fast GRE sequence, respiratory sinus arrhythmia can induce periodic SI increase by varying the respiratory rate interval and delay between images.

Deep venous thrombosis: gradient-recalled-echo MR imaging changes over time--experience in 10 patients.

PURPOSE: To determine the gradient-recalled-echo (GRE) magnetic resonance (MR) imaging changes caused by intraluminal thrombus of the lower extremities over time and to establish GRE MR imaging criteria to help distinguish acute from previous deep venous thrombosis. MATERIALS AND METHODS: Four women and six men, aged 38-76 years, underwent GRE MR imaging two to four time after the original diagnosis of deep venous thrombosis; eight also underwent confirmatory ultrasonography at that time. Follow-up was 3 months to 1 1/2 years. All patients were treated with anticoagulants. Evidence of thrombus, signal intensity characteristics, and MR imaging appearance were evaluated. RESULTS: Acute thrombosis was identified as an occlusion or prominent filling defect within the vessel. The luminal diameter of thrombosed veins was equal to or larger than that of a corresponding, unaffected vessel in each case. Acute thrombus signal intensity tended to be decreased initially and increase over time. Residual changes due to thrombosis included the web formation (n = 3), luminal narrowing (n = 4), and wall thickening and/or slow flow (n = 5). Vessels in three patients reverted to normal. CONCLUSION: GRE MR imaging demonstrated progressive changes of venous thrombus over time. These criteria may help distinguish acute deep venous thrombosis from the residual changes of previous thrombosis.

Quantification of myocardial perfusion by MRI after coronary occlusion.

The objectives of this study were to define the relationship between the first order constant of Gd-DTPA transfer (K1) and the myocardial blood flow (MBF) at rest and to compare it with an equivalent relationship obtained for positron emission tomography (PET). In a canine model of permanent coronary occlusion (n = 4), myocardial and blood time concentration curves obtained by 13N-ammonia PET and Gd-DTPA-enhanced MRI were fitted by a one-compartment model to determine K1. A linear relationship was observed between MRI-derived K1 and MBF measured by microspheres (K1 = 0.88 x flow -0.015, R = 0.95), which compares favorably with the equivalent relationship derived from PET (K1 = 0.74 x flow +0.16, R = 0.88). The results of this preliminary study suggest that, at rest and distal to a permanently occluded coronary artery, myocardial perfusion quantification by MRI is possible and can challenge PET.

Distal lower extremity arteries: evaluation with two-dimensional MR digital subtraction angiography.

PURPOSE: To test the hypothesis that magnetic resonance (MR) digital subtraction angiography is superior to two-dimensional time-of-flight (TOF) MR angiography for demonstration of patent arteries in the distal lower extremity. MATERIALS AND METHODS: Thirty-seven lower extremities in 23 consecutive patients were imaged with two-dimensional TOF MR angiography and two-dimensional MR digital subtraction angiography. Images were interpreted in a randomized and blinded manner. Each lower extremity was subdivided into seven potential arterial segments. The number of digital arteries visualized was also determined. Overall image quality of MR digital subtraction and TOF angiograms was compared. The relative ability of MR digital subtraction angiography and TOF MR angiography to demonstrate patent arterial segments was assessed. RESULTS: MR digital subtraction angiography was significantly superior to TOF MR angiography for demonstration of patent arterial segments and digital arteries (P < .001). MR digital subtraction angiographic images were qualitatively superior to TOF images (P < .001). CONCLUSION: Two-dimensional MR digital subtraction angiography is superior to two-dimensional TOF MR angiography for help in identifying patent segments in the distal lower extremity.

Bolus-chase MR digital subtraction angiography in the lower extremity.

A bolus-chase magnetic resonance (MR) angiographic technique performed with a prototypic stepping table and coil holder and a 15-20-mL injection of contrast material was developed to depict the entire lower extremity. Image acquisition was synchronized with passage of the contrast medium bolus through the lower extremity. Ten subjects underwent the examination, which was performed in less than 1 minute. All major arteries were well demonstrated in all cases.

Image is everything. New York Hospital's institution-wide digital imaging lowers costs and improves care.

UNLABELLED: The New York Hospital-Cornell Medical Center, Manhattan: a 1,242-licensed bed voluntary non-profit hospital. PROBLEM: Conventional imaging technology created expensive logistical problems between the radiology facility and the Greenberg Pavilion, a new 850,000 square foot, 11-floor inpatient tower, located two city blocks away. SOLUTION: Use a picture archiving communications system (PACS) to transmit, store and archive digital images. RESULTS: Increased staff efficiencies, improved patient care and reduced costs. KEYS TO SUCCESS: "Many years of planning and a full commitment from the staff."