Biomedical subjects
Publications and source records attributed to D G Mitchell.
A well-performed MR study early during the course of a patient's diagnostic evaluation for pancreatic disease may be a cost-effective alternative to a set of expensive and invasive tests. In this article, the spectrum of practical MR imaging techniques that can be valuable for diagnosing pancreatic disease is explored. Because many radiologists are inexperienced in pancreatic imaging, the technical parameters are emphasized.
Magnetic resonance imaging (MRI) can contribute to cost-effective management in women with suspected myomas or adenomyosis and can provide precise presurgical mapping prior to myomectomy or correction of müllerian duct anomalies. MRI is also valuable in patients with suspected adnexal masses that are not detected sonographically or where definitive diagnosis of juxtauterine myoma, cystic teratoma, or hemorrhagic mass may alter management.
We report the features of annular pancreas on magnetic resonance imaging in an asymptomatic adult. Fat suppressed T1-weighted imaging sequence demonstrated normal appearing pancreatic tissue encircling the duodenum, and depicted an aberrant ventral pancreatic duct.
Color Doppler imaging revealed a subclavian steal--retrograde flow in the right vertebral artery which shunted blood from the brain's posterior circulation to the right arm via the subclavian artery--in 17 of 54 infants (31%) during extracorporeal membrane oxygenation (ECMO); right vertebral artery flow returned to antegrade after ECMO and removal of the right common carotid arterial cannula. When subjects with and without a subclavian steal were compared, there were no statistically significant differences in mortality; in the results of neonatal electroencephalograms, cranial ultrasound studies, or computed tomography studies; or in early neurological development. Blood flow patterns and peak systolic velocities in the circle of Willis, middle cerebral arteries, internal carotid arteries, and basilar artery were similar in both groups during ECMO; blood flow velocity in the middle cerebral arteries was slightly but significantly lower on the right than the left in both groups. Our results indicate that increased flow in the left vertebral artery adequately compensated for the effect of a subclavian steal on the basilar and cerebral circulation. The moderate to marked neonatal electroencephalographic abnormalities commonly occurring during ECMO and the approximately 20% incidence of neurodevelopmental deficits among ECMO survivors remain largely unexplained.
PURPOSE: To compare contrast of abdominal tissue on magnetic resonance (MR) images obtained with T2-weighted conventional spin-echo (SE) and fast spin-echo (FSE) sequences. MATERIALS AND METHODS: Forty-eight patients (26 men and 22 women, aged 24-77 years) with known or suspected liver disease underwent FSE and SE MR imaging at 1.5 T. Signal intensity (SI) and ratios of signal-to-noise (S/N), signal difference-to-noise (SD/N), and SI were calculated for the spleen, pancreas, kidney, muscle, fat, and malignant liver lesions compared with liver. RESULTS: Significant differences were found between SD/N on FSE and SE images of all tissues, with FSE images providing lower SD/N for all tissues except fat. Malignant liver lesions (n = 69) showed lower SI ratios on the FSE compared with the SE images. Differences in mean SI ratios between malignant liver lesions and hemangiomas or cysts (n = 41) were significant on the FSE images (P = .01) but not on the SE images (P = .27). CONCLUSION: Compared with conventional T2-weighted SE images, small but significant differences in tissue-to-liver contrast were obtained for some tissues, including malignant liver lesions, on FSE images.
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PURPOSE: To determine if hepatic metastases can be distinguished from cavernous hemangiomas by pattern analysis of magnetic resonance (MR) images obtained prior to and following administration of gadoteridol at standard (0.1 mmol/kg) and triple (0.3 mmol/kg) doses. MATERIALS AND METHODS: Ninety-five patients with proved hepatic metastases (n = 71) or cavernous hemangiomas (n = 24) underwent MR imaging at 16 different institutions. T2-weighted spin-echo and T1-weighted images were obtained before and after gadoteridol administration. Two independent blinded reviewers rated individual features of benignancy versus malignancy on a five-point confidence scale. RESULTS: The most useful diagnostic features, with 100% specificity, were nodular enhancement for hemangiomas and rim enhancement for metastases. Confident (definitely benign or definitely malignant) diagnoses were rendered in 80 of 95 cases (84%), with an accuracy of a confident diagnosis of 96%. CONCLUSION: The pattern of enhancement on T1-weighted images is highly accurate for distinction between hemangiomas and metastases in images obtained with both doses.
PURPOSE: To assess the accuracy of using several criteria to evaluate endorectal coil magnetic resonance (MR) images for penetration of the prostatic capsule. MATERIALS AND METHODS: Thirty patients with prostate carcinoma underwent MR imaging and prostatectomy. Specified sites of potential capsular penetration on MR images were blindly evaluated by three readers for six diagnostic criteria. These evaluations were compared with pathologic findings of capsular penetration and were analyzed by means of receiver operating characteristic (ROC) analysis. RESULTS: The area under the ROC curve (Az) for the readers' overall impression of capsular penetration varied from .72 to .77. Highest mean Az's were for the criteria of capsular thickening (.74) and nodular extracapsular tumor (.72), although the latter finding had poor sensitivity (15%). Interobserver variation was low for all findings. CONCLUSION: Sensitivity and specificity were generally low for the diagnostic criteria. The usefulness of endorectal coil MR imaging in staging prostate cancer may be limited by the lack of diagnostic signs that uniformly identify extracapsular penetration.
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OBJECTIVE: Solid fibrotic nodules of endometriosis can simulate peritoneal metastases on imaging studies. To assist with this distinction, we analyzed the MR appearance of solid masses of pelvic endometriosis. MATERIALS AND METHODS: A search of pathologic and surgical records of patients who had pelvic MR imaging with a phased-array multicoil disclosed 13 patients who had endometriosis proved at laparotomy. MR images were reviewed retrospectively by two unblinded radiologists for the signal intensity, size, and enhancement pattern of solid peritoneal masses. Eight solid masses in six patients were detected on MR images: four lesions were in the cul-de-sac, two in the bladder wall, and two in the rectal wall. Four of the masses were excised at surgery and one was sampled by surgical biopsy; microscopy showed abundant fibrosis with small clusters of endometriotic glandular tissue. Three masses were inspected at surgery and found to represent dense fibrosis caused by endometriosis. RESULTS: Solid masses of endometriosis ranged in size from 1 to 5 cm. Seven of the eight masses had similar features on MR images: intermediate signal intensity on T1-weighted spin-echo images with punctate foci of high signal intensity, low signal intensity on T2-weighted images, and enhancement after administration of contrast material. CONCLUSION: MR imaging shows enhancing solid masses in some patients with endometriosis. These masses have MR features that might be useful in the differentiation between solid foci of endometriosis and peritoneal metastases.
Basic and more recent advances in imaging the pelvis are reviewed in this article. Commercially available innovations such as phased array multicoils in fast spin echo imaging can be used to improve resolution for MR imaging of the pelvis. Chemical shift imaging and vascular imaging in the pelvis also are reviewed, and potential roles for gadolinium-enhanced imaging and gastrointestinal contrast agents are discussed.
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During pregnancy, leiomyomas may cause complications such as spontaneous abortion, premature labor, and obstruction of labor. The conventional real-time ultrasound examination usually detects myomas adequately, but, in some cases, a local thickening of the uterine wall persists throughout the examination, interfering with the differentiation between myoma and contraction. In such cases, repeat scanning approximately 30 minutes later differentiates contractions, which usually resolve, from myomas. We examined 10 patients with B mode and color Doppler ultrasonography. In the 5 patients with myoma, we observed splaying of the vessels around the mass, whereas in the 5 patients with contraction, there was no vessel displacement in the area of the local myometrial thickening. The use of color Doppler and observation of these findings may obviate a prolonged ultrasound examination in questionable cases.
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Pulsation artifact on gradient echo images with ultrashort TE (i.e., < 3 msec) and intermediate TR is primarily from view-to-view amplitude modulation. Paramagnetic contrast agents increase the signal from blood during diastole without increasing the intensity of unsaturated systolic blood, decreasing signal modulation between systole and diastole. In a phantom and in humans, artifact decreased or remained the same following contrast enhancement.
Abdominal imaging studies may be performed for various indications in patients known to have sarcoidosis. To assess magnetic resonance imaging (MRI) and sonographic ability to detect abnormalities in sarcoidosis patients with abdominal involvement, a prospective study on 18 selected patients was performed. Besides organomegaly, when present, ultrasound demonstrated normal or increased hepatic parenchymal echogenicity, coarsening of the liver parenchyma with or without discrete nodules, focal calcifications, as well as contour irregularity. Splenic discrete nodules were seen on ultrasound in a single patient. Besides organomegaly, MRI abnormalities include abnormal hepatic signal intensity, discrete nodules, contour irregularity, speculation of small hepatic vascular branches, and a high periportal signal intensity. MRI splenic abnormalities include contour irregularity, nodularity, and abnormal signal intensity. The data presented in this study reveals the spectrum of ultrasound and MRI findings in sarcoidosis patients with abdominal organ involvement, potentially enabling the evaluation of the severity of the disease. MRI appears more sensitive than ultrasound for study of abdominal sarcoidosis.
We studied the range of appearance of asymptomatic patellar tendons and evaluated the effect of age, weight, joint effusions, and anterior cruciate ligament (ACL) tears on this tendon. One hundred and seventy-three patellar tendons in asymptomatic patients were studied at 1.5 tesla. Sagittal short and long TE images were evaluated in regard to tendon thickness, ratio of thickness of patellar to quadriceps tendons, frequency, location, and severity of intratendon signal, and frequency and severity of tendon buckling. Results were correlated with patient age, sex, weight, the presence of ACL tears, and relative volumes of joint fluid. The mean thickness of the patellar tendon was 0.52 cm. The patellar to quadriceps tendon ratio was 0.72. The patellar tendon frequently (74%) had focal areas of signal apparently within it. This signal was usually subtle, V-shaped (95%), and seen posteriorly in the proximal end of the tendon (82%). Intratendon signal was also seen commonly in the inferior aspect of the tendon (32%). This signal intensity did not increase with greater T2-weighting (99%). Buckling of the patellar tendon was a frequent asymptomatic variant (71%) but was also associated with joint effusions (p < 0.01) and ACL tears (p = 0.01). Buckling, intratendon signal, and tendon thickness increased with weight and age. Variation of the magnetic resonance appearance of the patellar tendon is frequent. Many of these changes appear to represent subclinical degeneration. Buckling of this tendon also may occur secondary to joint effusions or ACL tears.