Search PubMed⌕ Search

Biomedical subjects

D G Mitchell

Publications and source records attributed to D G Mitchell.

At least 73 records · Page 4Linked to original sources
PubMed1996

Normal ovaries and functional cysts: MR appearance.

PURPOSE: To evaluate characteristics of functional cysts and stroma in normal ovaries on magnetic resonance (MR) images. MATERIALS AND METHODS: Fifty-six women with at least one surgically proved normal ovary underwent MR imaging. Gadolinium-enhanced fat-saturated images were obtained in 32 patients. Ovary and cyst sizes and the number of cysts were recorded. Signal intensity was rated for the ovarian stroma and cysts. RESULTS: On T2-weighted images, 57 of 82 (70%) ovaries showed a zonal differentiation. Ovarian stroma enhanced less than myometrium in 30 of 43 cases. Zonal anatomy and degree of enhancement correlated with patient age and menopausal status. Cyst walls had lower signal intensity on T2-weighted images than ovarian stroma in 49 of 74 cases and showed greater enhancement in 21 of 35. CONCLUSION: Most normal premenopausal ovaries exhibit distinct features of a zonal anatomy, whereas postmenopausal ovaries do not. Cysts with discrete enhancing walls were numerous and were found in all age groups.

Adult↗
PubMed1996

Benign and malignant gynecologic disease: clinical importance of fluid and peritoneal enhancement in the pelvis at MR imaging.

PURPOSE: To correlate magnetic resonance (MR) imaging findings of pelvic fluid, peritoneal enhancement, and peritoneal nodules with the presence of benign or malignant pelvic disease. MATERIALS AND METHODS: Pelvic MR imaging findings in 87 women (mean age, 46 years) who subsequently underwent surgery were retrospectively reviewed. Phased-array multicoil, axial spin-echo T1-weighted MR images and axial fast spin-echo T2-weighted images were obtained. The largest pelvic fluid pocket was measured on the T2-weighted images in three orthogonal dimensions. Peritoneal enhancement and nodules were evaluated on gadolinium-enhanced MR images in 54 women. RESULTS: Pelvic fluid was shown in 21 of 25 patients with malignant neoplasms and 48 of 62 patients with benign disorders. Larger fluid pockets were associated with malignancy rather than with benign disorders, but there was substantial overlap. Use of peritoneal enhancement to diagnose peritoneal spread of tumor had a sensitivity, specificity, accuracy, and positive predictive value of 92% (11 of 12), 86% (36 of 42), 87% (47 of 54), and 65% (11 of 17), respectively. Use of peritoneal nodules for peritoneal spread had a higher specificity (90% [38 of 42]) and positive predictive value (69% [nine of 13]), although the sensitivity was lower (75% [nine of 12]). CONCLUSION: Large peritoneal fluid pockets are moderately predictive of malignancy or peritoneal spread of tumor. Peritoneal enhancement and enhancing peritoneal nodules are more sensitive and more specific.

Ascitic Fluid↗
PubMed1996

Renal lymphoma: demonstration by MR imaging.

OBJECTIVE: The objective of this study was to demonstrate the spectrum of appearances of renal lymphoma using current MR techniques including gadolinium enhancement. MATERIALS AND METHODS: Twelve patients with renal lymphoma were examined by MR imaging on a 1.5-T scanner. MR examinations included T2-weighted, breath-hold T1-weighted spoiled gradient-echo, and T1-weighted fat-suppressed spin-echo imaging before and after gadolinium administration. Tumor morphology, signal intensity, and enhancement features were evaluated. RESULTS: Three types of renal involvement were observed: large paraaortic retroperitoneal masses with extension into the renal hilum, the subcapsular space, or both (nine patients); unilateral diffuse infiltration of the renal parenchyma (one patient); and focal rounded intraparenchymal masses (two patients). Untreated lymphoma (10 patients) was slightly hypointense relative to the renal cortex on T1-weighted images and was heterogenous and slightly hypointense or isointense on T2-weighted images. Enhancement of lymphomatous tissue was mildly heterogenous and was minimal on early images after gadolinium enhancement and remained minimal on late contrast-enhanced images in most tumor masses. No central necrosis of tumor was identified, and no renal vein thrombus was present. Five patients with lymphoma that presented as a large paraaortic mass showed diminished renal cortical perfusion of the involved kidney. All of these patients also had tumor extension into the renal hilum. CONCLUSION: Three types of renal involvement with lymphoma were observed. The most common appearance was a large retroperitoneal mass that invaded the kidney. Tumors had low to intermediate signal intensity on T1- and T2-weighted images and had diffuse heterogenous enhancement that was less than that of renal parenchyma.

Adult↗
PubMed1996

Liver I: Currently available gadolinium chelates.

To use currently available gadolinium chelates most effectively, the liver should be imaged repetitively after contrast agent injection during hepatic arterial, portal vein, and delayed phases. Metastases usually demonstrate early as transient enhancement, which is often rim-shaped. Cavernous hemangiomas, however, demonstrate gradual clump-by-clump enhancement. Detection of hepatocellular carcinomas can be improved by use of dynamic scanning techniques. These and other principles of the use of currently available gadolinium chelates are reviewed in this article.

Contrast Media↗
PubMed1996

MR imaging techniques for evaluation of the pancreas.

New techniques have transformed magnetic resonance (MR) imaging of the pancreas from an imaging examination that had been inferior to computed tomography (CT) in diagnostic capability, to one that today may well be superior for many applications. These technologic advances include chemical-shift imaging, fast spin-echo T2-weighted imaging and its modifications, such as MR cholangiopancreatography, and dynamic gadolinium-enhanced imaging. Taken together, these techniques can detect diseases that may be difficult to appreciate on CT, such as small pancreatic adenocarcinomas, islet cell tumors, and ductal abnormalities and calculi. Newer intravenous contrast agents such as Mangafodipir, as well as oral contrast agents, have not been widely used but show promise for future improved pancreatic MR imaging.

Contrast Media↗
PubMed1995

Thickness of patellofemoral articular cartilage as measured on MR imaging: sequence comparison of accuracy, reproducibility, and interobserver variation.

OBJECTIVE: Since the thickness of cartilage is an important indicator of the status, progression and response to therapy of articular disorders, assessment of it is desirable. This study was undertaken to assess the accuracy, precision, and reliability of magnetic resonance (MR) measurements of articular cartilage. METHODS: Fifteen cadaveric patellas were imaged in the axial plane at 1.5 T. Gradient echo and fat-suppressed FSE, T2-weighted, proton density, and T1-weighted sequences were performed. We measured each 5-mm section separately at three standardized positions, giving a total of 900 measurements. These findings were correlated with independently performed measurements of the corresponding anatomic sections. A hundred random measurements were also evaluated for reproducibility and interobserver variation. RESULTS: Although all sequences were highly accurate (range r = 0.78-0.82), the T1-weighted images were the most accurate, with a mean difference of 0.25 mm and a correlation coefficient of 0.85. All sequences were also highly reproducible (mean difference between -0.09 and 0.05 mm) with little inter-observer variation (mean difference -0.04 and 0.11 mm). In an attempt to improve the accuracy of the MR measurements further, we retrospectively evaluated all measurements with discrepancies greater than 1 mm from the specimen. All these differences were attributable to focal defects causing exaggeration of the thickness on MR imaging. CONCLUSION: MR imaging is accurate, precise, and reliable as a basis for measuring articular cartilage and may potentially be usable to monitor progression of articular disorders. Care must be taken not to overestimate the thickness of areas with surface defects.

Adult↗
PubMed1995

Fat suppression by saturation/opposed-phase hybrid technique: spin echo versus gradient echo imaging.

The objective of the study was to compare hybrid opposed-phase fat suppressed sequences using gradient-echo (GRE) and spin-echo (SE) techniques. Eight normal volunteers had abdominal imaging at 1.5 T using both an opposed-phase fat-suppressed SE sequence (TR/TE 450/14) and an opposed phase GRE sequence (TE = 2.5) with frequency-selective fat suppression. Signal to noise ratios (SNR) and contrast to noise ratios (CNR) relative to fat of pancreas, liver and paraspinal muscle were calculated for each sequence. The GRE sequence with TR of 150 (25 s breath-hold) significantly outperformed the corresponding 3 min SE sequence for SNR and CNR for all tissues (p < .05). Hybrid opposed-phase fat-suppressed GRE sequences can be performed with breath-holding in less overall imaging time than SE sequences, and can achieve superior fat suppression and signal-to-noise if sufficient TR is used.

Abdomen↗
PubMed1995

Hepatic vascular diseases: CT and MRI.

Continued development of CT and MRI techniques has allowed these modalities to detect most hepatic vascular diseases, often obviating more invasive tests. In this article, the techniques for hepatic vascular diagnosis are reviewed, with emphasis on spiral CT and two-dimensional MRI techniques, and then the major vascular diseases on which these two modalities have a significant diagnosing impact are considered.

Budd-Chiari Syndrome↗
PubMed1995

Adrenal gland enhancement at MR imaging with Mn-DPDP.

PURPOSE: To determine adrenal gland enhancement with manganese (II) N,N' dipyridoxylethylenediamine-N,N'-diacetate 5,5'bis(phosphate) (DPDP) at magnetic resonance imaging. MATERIALS AND METHODS: After phase III trials, fat-suppressed, motion-compensated, T1-weighted spin-echo images (repetition time, 500 msec; echo time, 12 msec) of 13 consecutive patients were obtained at 1.5 T at one site, prior to and approximately 30 minutes after intravenous administration of 5 mumol/kg Mn-DPDP. Images were analyzed visually and by means of region-of-interest measurements, normalized to spleen. With data added from three more sites, enhancement of three adrenal adenomas and two metastases was analyzed. RESULTS: Twenty-five of 26 adrenal glands were depicted on MR images, and all showed enhancement. Mean adrenal enhancement (38%) was comparable to mean enhancement of liver (46%), pancreas (25%), and renal cortex (58%). Adrenal cortex and medulla could not be distinguished in nonenhanced or enhanced images. All three adrenal adenomas enhanced by more than 40%, but the metastases did not enhance. CONCLUSION: Functioning adrenal tissue (glands and at least some adenomas) are enhanced with Mn-DPDP.

Adenoma↗
PubMed1995

Rotator cuff disorders: interobserver and intraobserver variation in diagnosis with MR imaging.

PURPOSE: To determine interobserver and intraobserver variation in the interpretation of magnetic resonance (MR) images in rotator cuff disorders. MATERIALS AND METHODS: MR images of the shoulder in 97 patients were retrospectively reviewed twice, with a 3-week interval. Surgical findings indicated a full-thickness tear in 29 patients, grade 1 impingement in 19 (tendinitis), and grade 2 impingement (partial tear) in 26. The control population comprised 23 asymptomatic volunteers or patients. RESULTS: All observers were accurate in the diagnosis of a full-thickness tear (89%-98%), with good intraobserver (kappa = 0.67-0.84) and interobserver agreement (kappa = 0.74-0.92). In diagnoses of tendinitis, partial tear, and normal cuff, there were wide ranges of sensitivity (13%-74%) and specificity (72%-93%), as well as poor interobserver (kappa = 0.12-0.60) and intraobserver agreement (kappa = 0.35-0.78). CONCLUSION: Full-thickness tears of the rotator cuff can be accurately identified at MR imaging with little observer variation. Consistent differentiation of normal rotator cuff, tendinitis, and partial thickness tears is more difficult.

Female↗
PubMed1995

Early hepatocellular carcinoma that develops within macroregenerative nodules: growth rate depicted at serial MR imaging.

PURPOSE: To assess by means of magnetic resonance (MR) imaging the growth rate of early hepatocellular carcinoma (HCC) that develops within macroregenerative nodules. MATERIALS AND METHODS: Serial MR imaging was performed in five patients with six macroregenerative nodules that demonstrated a "nodule-within-nodule" pattern (small intranodular focus). The diameter and volume increases of the internal foci at different time intervals were estimated. Average doubling time (DT) was then calculated. RESULTS: The tiny foci within macroregenerative nodules exhibited rapid growth, with average DTs of 29 weeks for diameter and 9.5 weeks for volume. HCC was proved histopathologically in all five patients. CONCLUSION: HCC, which manifests initially as a small focus within a macroregenerative nodule, has the potential for rapid growth. This growth rate should be considered when plans are formulated for follow-up and/or treatment.

Aged↗
PubMed1995

MR imaging: quality assessment method and ratings at 33 centers.

PURPOSE: To outline a quality assessment method with peer review for magnetic resonance (MR) imaging. MATERIALS AND METHODS: Thirty-three providers in the Philadelphia area were rated on a random sample of 132 brain, 124 cervical spine, and 113 lower extremity MR imaging examinations performed during 1990. Blinded peer review was performed by panels of three subspecialty-trained academic radiologists. Technical performance, completeness, and report appropriateness of each MR imaging examination were evaluated. Aggregated scores were calculated to rate provider performance for each of the three parameters of quality. RESULTS: Two or three panelists assessed technical performance as inadequate in 15 cases, completeness as incomplete in 58 cases, and the interpretative report as inappropriate and affecting treatment in 72 cases. Eleven providers received an unsatisfactory rating on one or more parameters of quality. The association between unsatisfactory ratings and the use of low-field-strength (< or = 0.6-T) imagers was statistically significant (P < .008). CONCLUSION: Substantial deficiencies were identified in the performance of examinations and interpretation of MR images in the Philadelphia area in 1990. These findings indicate the need for a program to monitor quality of MR imaging.

Brain↗
PubMed1995

Distinction between benign and malignant adrenal masses: value of T1-weighted chemical-shift MR imaging.

OBJECTIVE: Accuracy of T1-weighted chemical-shift MR imaging for the differentiation between benign and malignant adrenal masses was blindly assessed among three radiologists. SUBJECTS AND METHODS: MR imaging was performed at 1.5 T in 50 patients with 58 adrenal masses, proved benign (n = 38) or malignant (n = 20) based on surgery or growth (malignant) or stable size (benign) for at least 1 year. In-phase spin-echo sequences or in-phase breath-hold fast multiplanar spoiled gradient-recalled echo (FMPSPGR) sequences with a TE of 4.2 msec were compared with opposed-phase breath-hold FMPSPGR sequences with a TR/TE of 35-155/2.2-2.9 and a 90 degrees flip angle for the detection of lipid in adrenal masses. Three radiologists who were blinded to diagnosis and clinical data independently rated the likelihood of a benign adrenal lesion on a five-point scale of confidence. RESULTS: Mean sensitivity, specificity, and positive predictive value for a definite or probable diagnosis of a benign lesion by the three readers were 87%, 92%, and 95%, respectively. At the highest (definite) confidence of a benign lesion, the mean positive predictive value was 99%, with lower sensitivity (54%). Areas under receiver operating characteristic curves for the three radiologists were .98 (95% confidence interval [CI] = .94-1.00), .96 (CI = .91-1.00), and .95 (CI = .89-1.00). Interobserver variation for the diagnosis of a benign mass was low (kappa = .79). CONCLUSION: Chemical-shift imaging using breath-hold opposed-phase T1-weighted MR images is a reliable and reproducible technique for the diagnosis of most benign adrenal masses at the highest threshold of confidence.

Adrenal Gland Neoplasms↗
PubMed1995

Gadoteridol-enhanced MR imaging of malignant hepatic tumors: effects of triple versus standard doses on lesion-liver contrast.

OBJECTIVE: The purpose of this study was to compare liver signal-to-noise ratio (SNR), lesion SNR, and lesion-liver contrast-to-noise-ratio (CNR) in patients with malignant liver lesions after the administration of a standard dose (0.1 mmol/kg of body weight) or a triple dose (0.3 mmol/kg) of a gadolinium chelate (gadoteridol). We hypothesized that the higher dose would produce a higher lesion-liver CNR and therefore increase the conspicuity of hepatic lesions. MATERIALS AND METHODS: A total of 85 patients with malignant hepatic masses (61 metastases, 22 hepatocellular carcinomas, and two lymphomas) proved by histologic or follow-up studies underwent MR imaging at 1.5 T. T1-weighted spin-echo imaging and gradient-echo imaging were done before and within 1 min after (gradient echo) as well as 5 (spin echo) and 15 (spin echo) min after the injection of 0.1 or 0.3 mmol of gadoteridol per kg, randomized before the start of the study (39 patients received the standard dose, and 46 received the triple dose). The signal intensities of the liver and lesions and the SD of background noise were measured by use of regions of interest to calculate the SNR of the liver and malignant lesions and the lesion-liver CNR. RESULTS: The lesion-liver CNR was increased significantly at 5 and 15 min after the administration of gadoteridol. No significant differences in the liver SNR, lesion SNR, and lesion-liver CNR (after 1 min: standard dose, -5 +/- 8, and triple dose, -4 +/- 14; after 5 min: standard dose, -1 +/- 5, and triple dose, 2 +/- 8; and after 15 min: standard dose, 1 +/- 5, and triple dose, 6 +/- 20) were found between the doses at all time points. CONCLUSION: Triple-dose gadoteridol does not improve the lesion-liver contrast of malignant hepatic lesions over that provided by the standard dose and is not warranted for liver MR imaging.

Adult↗