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Biomedical subjects

D G Mitchell

Publications and source records attributed to D G Mitchell.

250 records · Page 14Linked to original sources
PubMedDate not supplied

Marrow infarction in sickle cell anemia: correlation with marrow type and distribution by MRI.

Ischemic necrosis of bone is believed to occur exclusively in areas of predominantly fatty marrow. Sickle cell disease is unusual in that marrow infarction occurs in areas of active hematopoiesis. MR images of long bone obtained in ten patients with sickle cell anemia (SCA) were analyzed to correlate the distribution and appearance of marrow infarction with the type of marrow. While the hematopoietic marrow predominated in metaphyseal and diaphyseal regions of femurs and tibias, the fatty or mixed marrow was the most common pattern in epiphyses. Infarcts occurred in fatty as well as hematopoietic marrow. Marrow infarcts were isointense or minimally hyperintense on T1 weighted images with the hematopoietic marrow and therefore difficult to detect. On T2 weighted images, the infarcts showed very high signal. T2 weighted images are essential for detection of marrow infarction. Soft tissue changes seen as low signal on T1 and high signal on T2, may be secondary to intramuscular injections of analgesics or muscle ischemia occurring during sickle crisis.

Adult↗
PubMedDate not supplied

Multiple actinomycotic liver abscesses: MRI appearances with etiology suggested by abdominal radiography. Case report.

The magnetic resonance imaging appearances of multiple actinomycotic liver abscesses are described. The abscesses appeared hypointense to liver parenchyma on T1-weighted sequences and hyperintense on T2-weighted sequences with some surrounding edema. Following intravenous gadolinium diethylenetriamine-pentaacetic acid, the masses showed a thick enhancing rim but no central enhancement. Although no etiology was discovered in the initial clinical history, antecedent dental surgery was evident on abdominal radiography that depicted dental amalgam in the ascending colon.

Abscess↗
PubMedDate not supplied

MRI of benign and malignant hepatic lobar atrophy.

We assessed the magnetic resonance imaging (MRI) features of hepatic lobar atrophy. Two of us reviewed MRIs of the liver in eight patients with benign or malignant forms of lobar atrophy. All atrophic lobes showed low signal intensity on T1-weighted images and high signal intensity on T2-weighted images compared with the remainder of the liver, and all showed greater enhancement compared to the nonatrophic lobe. Atrophic lobes have suggestive MRI findings and are similar for both benign and malignant etiologies.

Adult↗
PubMedDate not supplied

Gastrografin versus dilute barium for colonic CT examination: a blind, randomized study.

Fifty patients receiving oral contrast medium the day of their CT examinations were studied to evaluate colonic opacification. Two groups were given small volumes (20 versus 30 ml) of nondilute diatrizoate meglumine/diatrizoate sodium (Gastrografin) the night prior to examination and were compared with groups receiving no contrast medium (control) or a large volume (600 ml) of dilute barium the night prior to examination. Frequency of total colonic opacification was as follows: 30 ml Gastrografin, 92%; 20 ml Gastrografin, 71%; dilute barium, 46%; and control, 9%. Significant artifact was infrequent in all groups. Administration of small volumes of nondilute Gastrografin is a well tolerated, inexpensive, and effective method for opacifying the colon for CT.

Barium Sulfate↗
PubMedDate not supplied

Improvement in signal-to-noise ratio and reduction of chemical shift and motion-induced artifacts by summation of gradient and spin echo data acquisition.

Narrow bandwidth magnetic resonance (MR) imaging allows an increase of signal-to-noise ratio (SNR) but causes increased chemical shift and motion-induced artifacts. To obtain MR images with SNR approximately equal to that obtained with narrow bandwidth but with less chemical shift and motion-induced artifact, we introduced triple readout gradient reversal centered around the spin echo. As a result, signals from two gradient echoes and a single spin echo can be collected and summed. Phantom, knee, shoulder, and abdominal MR images were obtained using a 1.5 T GE Signa System at sampling rates ranging from 10 to 60 kHz. Since the bandwidth per pixel was tripled, chemical shift misregistration was reduced by the same factor. The summation image of two gradient echoes and one spin echo had an SNR comparable with that of a single spin echo acquired within the same total sampling interval. Data acquisition at a high sampling ratio also minimizes the dispersion of T2* weighting among three echoes. In addition, summation of the three resulting images decreases motion artifact by effective averaging.

Abdomen↗
PubMedDate not supplied

Hepatocellular tumors with high signal on T1-weighted MR images: chemical shift MR imaging and histologic correlation.

We reviewed conventional and chemical shift MR images and histologic findings of seven proven primary hepatic masses that had higher signal than liver on T1-weighted images to determine if this necessarily indicates fat and if the presence of fat indicates malignancy. These seven masses included five hepatocellular carcinomas (HCCs), one focal nodular hyperplasia (FNH), and one fatty dysplastic nodule. An eighth solitary high signal mass without histologic proof had evidence of abundant fat on each of two chemical shift MR images 25 months apart. Only one of the five HCCs had chemical shift or histologic evidence of fat, while the FNH and dysplastic nodule each had both chemical shift and histologic confirmation of fat. The dysplastic nodule became more dysplastic and grew significantly within 14 months, but remained benign. The unproven fatty lesion decreased in size over 25 months and is therefore presumably benign. Although no statistical inferences can be drawn from this small correlative study, we have shown that HCC may have higher signal intensity than liver on T1-weighted images, whether or not it contains fat. Chemical shift techniques can confirm the presence of intratumoral fat and thus indicate a mass of hepatocellular origin, but the mass may be benign or malignant.

Biopsy↗
PubMedDate not supplied

MRI of pancreatic gastrinomas.

Pancreatic islet cell tumors are often small and multiple, and preoperative diagnosis can be difficult. In a woman with hypergastrinemia, angiography and CT each depicted a solitary lesion. Magnetic resonance images, acquired using fat suppression, fast spin echo, and contrast material injection, depicted seven separate lesions, which were surgically confirmed.

Adult↗
PubMedDate not supplied

Pancreatic beta-cell tumors: MRI.

Ten consecutive patients with surgically proven beta-islet cell tumors, strongly suspected clinically because of positive laboratory findings, were studied by MRI at 0.5 T. Results were correlated with CT and angiography. MRI detected all 10 insulinomas, with the location confirmed at surgery. Lesion size was < 1 cm in three cases, between 1 and 2 cm in five cases, and between 2 and 3 cm in two cases. A false-negative diagnosis was obtained with CT in 6 of 10 and with angiography in 3 of 10 cases. Our results suggest that if motion artifact can be controlled or reduced, MRI can be employed to localize insulinomas in patients with positive clinical and laboratory findings.

Adolescent↗
PubMedDate not supplied

Abdominal iron distribution in sickle cell disease: MR findings in transfusion and nontransfusion dependent patients.

OBJECTIVE: Our goal was to determine the difference in iron distribution between transfusion dependent (TD) and nontransfusion dependent (NT) patients with sickle cell disease (SCD). MATERIALS AND METHODS: The T2-weighted and T2*-weighted abdominal MR images in nine cases of homozygous SCD were reviewed to determine the distribution of low signal from iron in five TD and four NT patients. RESULTS: All eight patients with visualized spleens had decreased splenic signal intensity. One patient who had no history of splenectomy had no visualized splenic tissue. The majority of both groups had renal cortex of low signal intensity that was attributable to iron deposition from intravascular hemolysis and was not correlated with clinical renal abnormalities. None of the NT group had liver or pancreas of low signal intensity, while all five TD patients had decreased liver signal intensity and three of five had decreased pancreatic signal intensity. CONCLUSION: Decreased pancreatic signal intensity can occur in TD patients, perhaps suggesting total body iron overload. Nontransfusion dependent sickle cell patients usually have normal hepatic signal intensity and do not have total body iron overload, even in the presence of renal and splenic iron deposition.

Abdomen↗
PubMedDate not supplied

Hepatocellular carcinoma after systemic chemotherapy: gadolinium-enhanced mr measurement of necrosis by volume histogram.

As a preliminary study, we measured the necrosis of advanced hepatocellular carcinoma (HCC) by volume histogram after systemic chemotherapy and correlated it with clinical data. Five patients with advanced HCC secondary to chronic hepatitis and cirrhosis underwent pretreatment and posttreatment MR examination on a 1.5 T MR scanner following systemic chemotherapy. MR sequences included dynamic enhanced fast spoiled gradient echo 3D images. Clinical response to chemotherapy, as determined by MR images, was measured as changes of both the total tumor volume and the percent of tumor necrosis by volume histogram algorithm. Four of five patients had clinical improvement. Three of these patients had no or minimal change of tumor volume; however, there was an increase in tumor necrosis in follow-up MR image. One patient of five with no change in tumor necrosis had no response and died at 3 months. Serial MR images showed increased irregular necrosis of advanced HCC after systemic chemotherapy, but stable volume, in patients who responded clinically to systemic chemotherapy.

Antineoplastic Combined Chemotherapy Protocols↗
PubMedDate not supplied

Biphasic contrast-enhanced multisection dynamic MR imaging of the liver: potential pitfalls.

Biphasic contrast material-enhanced dynamic magnetic resonance (MR) imaging is an important technique for evaluating liver disease. However, several potential diagnostic pitfalls may be encountered, including lobar, segmental, subsegmental, and subcapsular hyperperfusion abnormalities; early-enhancing pseudolesions, particularly in the medial segment of the left hepatic lobe; heterogeneous hyperperfusion abnormalities throughout the liver; and hypointense pseudolesions due to vascular artifacts, unenhanced hepatic vessels, partial volume artifacts, magnetic susceptibility artifacts, and regenerative nodules in cirrhosis. These abnormalities sometimes have appearances similar to those of true lesions or tumor spread to the surrounding liver parenchyma on arterial-dominant phase dynamic MR images. In most cases, however, no corresponding abnormalities are seen with other pulse sequences or on delayed-phase MR images. In addition, hyperperfusion abnormalities due to readily recognizable causes are often found in characteristic locations and thus can be differentiated from true tumors. An understanding of the causes of these potential pitfalls and how to avoid them will help radiologists understand and correctly interpret images.

Artifacts↗
PubMedDate not supplied

CT of acquired abnormalities of the portal venous system.

Computed tomography (CT), including biphasic contrast material-enhanced helical dynamic scanning and three-dimensional CT angiography, is useful in evaluating acquired abnormalities of the portal venous system. At contrast-enhanced CT, portal venous thrombus usually manifests as low-attenuation intraluminal lesions combined with enlargement of the affected portal vein. Cavernous transformation, a masslike network of intertwined veins that provides an alternative pathway for a stenosed or occluded portal vein, is depicted as multiple, periportal vascular structures. At helical dynamic CT, arterioportal shunts manifest as early enhancement of the affected portal vein, transient hyperperfusion abnormalities with lobar or segmental distribution, or transient wedge-shaped enhancement peripheral to the tumor. In patients with portosplenic venous invasion by malignant neoplasms, peripancreatic or perigastric veins may dilate if they function as hepatopetal collateral veins. In patients with portal hypertension, a variety of hepatofugal collateral pathways can develop, including esophageal, paraesophageal, coronary gastric, inferior phrenic, paraumbilical, abdominal wall, splenorenal, gastrorenal, retrocaval, and mesocaval collateral pathways. An understanding of the varied CT appearances of acquired abnormalities of the portal venous system will allow more definitive diagnosis and help avoid false diagnosis of disease.

Collateral Circulation↗
PubMedDate not supplied

Recovery of native liver after heterotopic liver transplantation for fulminant hepatic failure: MR studies.

Heterotopic liver transplantation involves the transplantation of an auxiliary liver into the subhepatic space while leaving the native liver intact. This procedure is a viable treatment for select patients with fulminant hepatic failure who fail medical treatment. The MR-pathologic correlation of a patient who developed graft failure and recovered full function of her native liver after heterotopic liver transplantation is presented. Based on the imaging and biopsy findings, immunosuppression was withdrawn and the patient remains asymptomatic with normal liver function. Interpreters of imaging studies in this group of patients should not restrict their attention to the heterotopic graft. The return of the native liver in both a structural and functional sense is a clinically important phenomenon that can be detected with MR imaging.

Adult↗
PubMedDate not supplied

Acute renal allograft rejection: difficulty in diagnosis of histologically mild cases by MR imaging.

To determine the ability of magnetic resonance (MR) imaging to diagnose various degrees of acute allograft rejection (AR), 33 MR examinations in 28 patients were obtained. Surface coils were used in 21 examinations. Seventeen examinations were correlated with biopsy results, which were graded as absent (n = 7), mild (n = 6), or severe (n = 4) AR. Corticomedullary differentiation (CMD) on T1 weighted images was graded as absent/poor versus distinct, and images were also evaluated for visibility of intrarenal vessels. For serial examinations, renal volume was measured and compared. The MR results were correlated with radionuclide interpretations in 22 cases. Diminished CMD was most common with AR (7 of 12) but was also seen with acute tubular necrosis (2 of 6) and cyclosporin toxicity (2 of 3). All four cases of severe AR had diminished CMD. In contrast, only one of six cases of mild AR had diminished CMD (p less than 0.05). Four of five cases of mild AR by radionuclide scan were correctly diagnosed. Visualization of intrarenal vessels was best with surface coils, but this did not contribute to differential diagnosis. Renal volume was increased in rejecting allografts. Magnetic resonance is a promising modality for investigation of renal allografts but is not a sensitive or specific modality for the diagnosis of mild AR.

Graft Rejection↗
PubMedDate not supplied

Obstructive jaundice due to multiple myeloma of the pancreatic head: CT evaluation.

Extraskeletal spread of multiple myeloma is common and may cause jaundice due to hepatic infiltration. Less commonly, involvement of the pancreas may cause obstructive jaundice. We present a patient with multiple myeloma who became jaundiced. Computed tomography revealed an obstructing pancreatic mass. Aspiration biopsy yielded clumps of atypical plasma cells. The mass and the patient's jaundice responded satisfactorily to local radiation treatment.

Aged↗