David Thickman

Diagnosis of pneumoperitoneum : abdominal CT vs. upright chest film

To compare the sensitivity of CT with upright chest radiography for the detection of free intraperitoneal air, we compared the results of these examinations performed on trauma patients who had introduction of intraperitoneal air from diagnostic peritoneal lavage (DPL). Thirteen patients were studied by abdominal CT within 24 h after DPL. Upright chest radiography was performed prior to abdominal CT or <4 h after abdominal CT. All patients demonstrated free air on abdominal CT. Only 5 of 13 (38%) patients demonstrated free air on plain radiography. The amount of free air demonstrated on CT was quantified into three groups. Upright chest radiography in the minimal group (less than three 1 mm pockets of air) was totally insensitive (0 of 2) in detecting free air. Upright chest radiography in the moderate group (greater than three 1 mm pockets, but <13 mm diameter collection of air) was 33% sensitive (3 of 9). Upright chest radiography in the large group (>13 mm collection of air) was 100% sensitive (2 of 2). Abdominal CT is clearly superior to upright chest radiography in demonstrating free intraperitoneal air in this clinical setting.

Magnetic resonance imaging of avascular necrosis of the femoral head

This study investigates the role of magnetic resonance imaging (MR) in identifying avascular necrosis (AVN) of the femoral head and in monitoring its therapy. The detection of AVN, particularly in its early stages, is imperative to give therapeutic intervention the best opportunity for successful management. The results of magnetic resonance imaging are compared with those of the standard diagnostic modalities in evaluation of patients with the lesion. Examinations were performed at 0.12 T with a repetition time (TR) of 143 ms and times to echo (TEs) of 10 or 20 ms. This study represents a retrospective review of 90 hips which were examined in 45 consecutive patients. Of these, 52 hips were biopsied as part of treatment. MR was shown to be sensitive in the detection of AVN. Comparison of MR with radionuclide imaging showed comparable sensitivity and specificity. MR was also noted to be sensitive in the detection of early AVN. Preliminary results suggest that MR can monitor treatment of the affected hip, and may even be able to predict patient response to therapy. Although further work is necessary to determine the role of MR in the evaluation of the patient presenting with hip pain, MR is a sensitive method in detecting AVN and in monitoring its course in patients suspected of having the disease.

Searching for lung nodules. A comparison of human performance with random and systematic scanning models.

The contrast sensitivity of the retina is greatest in the center and decreases rapidly toward the periphery. Therefore, the detection of low-contrast lung nodules depends upon the manner in which the image is sampled by retinal receptors as eye fixations jump across the image during scanning. The scanning performance of two radiologists was compared with two computed models, a systematic and a random scanner. Although radiologists do not seem to have random scanning patterns, their coverage of the image was matched more closely by the random model. This suggests that radiologists employ a scanning strategy that is designed to cover the image of the lungs in a minimum time using the smallest possible visual field. The visual field size that is most effective in detecting nodules during search has a radius of 3.5 degrees visual angle. Nodule detection may be limited by basic neurologic constraints on human scanning performance.

Coronary CT angiography findings in patients without coronary calcification.

OBJECTIVE Coronary calcification detected by CT is a marker for atherosclerotic disease with prognostic significance. However, potentially unstable plaque is characterized by a high lipid content rather than calcification, which may make detection using the calcium score difficult. To assess the prevalence and severity of atherosclerotic disease in patients without coronary calcification, we evaluated findings in patients with a normal calcium score undergoing coronary CT angiography (CTA). MATERIALS AND METHODS Data from 794 consecutive coronary CTA examinations performed between February 2005 and May 2007 were reviewed. The calcium scores were determined as part of coronary CTA examinations, and calcium was quantified according to the Agatston method. Patients underwent coronary CTA because of high risk for coronary artery disease (53%) or atypical symptoms or abnormal stress test results (47%). On coronary CTA, plaque was characterized as mild disease without hemodynamically significant stenosis, moderate disease without hemodynamically significant stenosis, moderate stenosis (50-70% luminal narrowing), or severe stenosis (> 70% luminal narrowing). RESULTS Of the 729 patients included in the study, 325 (45%) had a normal calcium score. Of these, 167 (51%) had noncalcified plaque on coronary CTA. Twelve (3.7%) of those with a normal calcium score had at least moderate stenosis, five (1.5%) of whom had severe stenosis. Eight of the 12 patients with significant stenosis underwent invasive angiography and coronary stenting. CONCLUSION A considerable atheroma burden including significant stenoses may be present in patients with no coronary calcification. Although the calcium score does add prognostic value to standard risk factors and serum markers, imaging the vessel wall directly may be helpful to identify noncalcified plaque and guide therapy.

MR imaging of cerebral abnormalities in utero

In view of the lack of ionizing radiation, ability to image in a variety of planes, and high contrast resolution, magnetic resonance (MR) imaging may have a role in obstetrical management. Three fetuses with severe cerebral abnormalities were studied by MR in utero. The findings were correlated with ultrasound examinations and with autopsy results. Ventricular dilatation and progression of hydrocephalus were detected by MR. Although fetal motion may affect image quality, diagnostically useful images were obtained with imaging times of 2.5 min.

Mr Imaging of Fetal Brain

Magnetic resonance (MR) imaging was used to evaluate normal fetal intracranial anatomy in axial, coronal, and sagittal planes. The T1 and T2 weighted images (WI) of aborted fetuses of varying gestational ages were correlated with anatomic sections. In the premature fetus three distinct intensity zones were seen on MR that were not visualized on gross specimens. Unmyelinated white matter displays low intensity on T1 W1 and high intensity on T2 W1. Maturational changes of the brain were observed with advancing fetal age.

Vicarious excretion of water-soluble contrast media into the gallbladder in patients with normal serum creatinine.

Ten patients with normal serum creatinine and no evidence of acute cholecystitis were found to have vicarious excretion of water-soluble contrast media into the gallbladder 20 minutes to 72 hours after injection. Eight of the ten had unilateral renal pathology. Two patients, however, had bilaterally normal kidneys. The patients had been injected with either diatrizoate, iothalamate, or iodamide. The mechanisms and pathophysiology of vicarious contrast excretion are discussed. The vicarious excretion of intravascular contrast in the gallbladder does not in itself indicate renal or hepatobiliary disease. Although commonly associated with unilateral renal pathology, vicarious gallbladder excretion of urographic contrast may be a normal variant in some patients.

Nuclear magnetic resonance imaging in gynecology

Nuclear magnetic resonance proton imaging is a new imaging technique that holds promise for gynecologic diagnosis. Without the use of ionizing radiation, it provides images with excellent definition of the major pelvic organs. The extent and nature of disease are well demonstrated. In this report, an introduction to the principles of nuclear magnetic resonance imaging is given and several clinical examples that reveal the potential uses of nuclear magnetic resonance imaging in the female pelvis are shown.

MR IMAGING OF THE MEDIASTINUM: A RETROSPECTIVE COMPARISON WITH COMPUTED TOMOGRAPHY

Magnetic resonance (MR) imaging of the mediastinum was performed with a 0.12 T resistive magnet and compared with the results of CT. On T1 weighted images with partial saturation technique, soft tissue masses, lymphadenopathy, lipomatosis, and vascular anatomy were comparable with MR and CT imaging in 19 of 30 patients (63.3%). In the remaining 11 patients only slight differences between the two modalities were observed. Our experience suggests that MR imaging at low field strength is equivalent to CT in the morphologic assessment of the mediastinum without the need for administration of intravenous contrast medium or exposure to ionizing radiation.

CT of melanoma liver metastases : is the examination without contrast media superfluous ?

The current method of evaluating hypervascular liver metastases with CT includes both contrast enhanced and unenhanced studies. The necessity of performing both examinations for the detection of liver metastases in the workup of malignant melanoma has not been specifically addressed. This study evaluates potential additional information derived from an unenhanced examination of the liver. We studied 55 patients with malignant melanoma who had both contrast enhanced and unenhanced CT examinations performed during the workup and staging of their disease. Sixteen patients had 89 measurable liver lesions seen on enhanced CT. Three patients had liver lesions that were too numerous to accurately measure. Unenhanced CT demonstrated only 62% of the measurable lesions. All liver lesions seen on the unenhanced images were identified on the enhanced studies. Only one metastasis was found to be comparatively smaller on the enhanced examinations. The unenhanced examinations detected no additional lesions. It is reasonable to perform only an enhanced examination during the workup and staging of malignant melanoma liver metastases.