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Biomedical subjects

D G Mitchell

Publications and source records attributed to D G Mitchell.

At least 235 records · Page 13Linked to original sources
PubMedDate not supplied

MR imaging contrast agents--what's in a name?

The purpose of this brief review is to reduce the confusion surrounding the nomenclature of MRI contrast agents. There are several different categories of contrast agents for potential use in human diagnosis and several alternative names for each contrast agent, an array of choices that actually changes over time. This review describes the general process by which these various agents are named, presents one general categorization by which these agents can be considered, and provides a concise table to which readers can refer to identify the proper name to use for each of the agents that has thus far been administered to humans.

Administration, Oral↗
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Breath-holding in healthy and pulmonary-compromised populations: effects of hyperventilation and oxygen inspiration.

Suspension of respiration during end-expiration often is recommended to minimize body organ displacement between sequential image acquisitions. The purpose of this report is to evaluate techniques for end-expiratory breath-holding applicable to a pulmonary-compromised population. Eighty-seven consecutive outpatients with chronic pulmonary diseases and 31 healthy nonsmoking volunteers were recruited for the study. All subjects were asked to hold their breath in end-expiration while in the supine position (29 after breathing room air, 29 after hyperventilating room air for six breaths, and 29 after breathing O2 from a portable oxygen tank via nasal cannula until pulse-oximeter readings stabilized or reached 100%). Each volunteer was tested with all three methods. The mean length of time for a breath-hole on room air without hyperventilation was 9.2 seconds for the patients and 31.7 seconds for the volunteers. A breath-hold after hyperventilation of room air was timed at 12.3 seconds for the patients and 41.2 seconds for the volunteers, and after O2 administration, the breath-hold was 22.4 seconds for the patients and 60.9 seconds for the volunteers. No adverse effects occurred. The pulmonary-compromised patient can suspend respiration most successfully after O2 administration (P < .0001), whereas hyperventilation seems to be less beneficial. Nonpulmonary-compromised volunteers can hold their breath for longer periods of time.

Adult↗
PubMedDate not supplied

Rapidly enhancing hepatic hemangiomas at MRI: distinction from malignancies with T2-weighted images.

The purpose of this study is to describe a subset of atypical hepatic hemangiomas that enhance rapidly and diffusely and to determine whether heavily T2-weighted images could distinguish between atypically enhancing liver hemangiomas and hypervascular malignancies. A retrospective search of MR records identified seven patients with liver hemangiomas that demonstrated diffuse early enhancement and 23 patients with biopsy-proven malignant liver lesions that were hypervascular on dynamic gadolinium-enhanced MR images. Quantitative analysis of signal intensity measurements was performed on the T2-weighted images, heavily T2-weighted (TE > 140), and dynamic gadolinium-enhanced images. Blinded reader comparison of the T2-weighted images and gadolinium-enhanced images was performed. Hypervascular hemangiomas enhanced to a greater degree than hypervascular malignant liver lesions on the early phase gadolinium-enhanced images. Perilesional parenchymal enhancement was demonstrated in five cases of rapidly enhancing hemangiomas. Signal intensity and contrast-to-noise ratios on the heavily T2-weighted images of the hemangiomas were significantly greater than that of the hypervascular malignant lesions (P < .05). Hemangiomas were differentiated from the hypervascular malignant liver lesions with high accuracy (97-100%) by three blinded readers based on the T2-weighted images. A subset of hemangiomas have atypical rapid diffuse enhancement on dynamic gadolinium-enhanced images. These atypical hemangiomas can be distinguished from hypervascular malignant liver lesions on T2-weighted MR images.

Adult↗
PubMedDate not supplied

Biliary cystadenoma with mesenchymal stroma of the liver: correlation between unusual MR appearance and pathologic findings.

We reported a case of the biliary cystadenoma of the liver. The cystic mass had lobulation and septation and showed marked hyperintensity on T1-weighted images and hypointensity on T2-weighted images; MR findings were very unusual for cystadenoma. The content of the cystic mass was jelly-like, thick mucinous fluid without intracystic hemorrhage. We concluded that these unusual signal intensities of the cyst were due to hyperproteinous mucinous fluid.

Adenoma, Bile Duct↗
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Sinusoidal spread of liver metastases from renal cell carcinoma: simulation of diffuse liver disease on MR imaging.

Rarely, hepatic metastases can simulate hepatic infiltrative diseases. We present a case of a patient with advanced metastatic renal cell carcinoma who developed hepatomegaly and clinical signs of hepatocellular injury. On magnetic resonance imaging, the injury simulated a diffuse process, e.g., acute fulminant viral or chemical hepatitis or drug toxicity. Despite its high resolution, magnetic resonance imaging might not depict focal lesions in patients with extensive metastases. In correlation with clinical history, malignant disease should be considered when diffusely abnormal hepatic signal intensity is noted.

Carcinoma, Renal Cell↗
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Hepatic iron deposition on MR imaging in patients with chronic liver disease: correlation with serial serum ferritin concentration.

BACKGROUND: To evaluate the relationship between magnetic resonance (MR) imaging grading of iron deposition and serial serum ferritin concentration in patients with chronic viral liver diseases. METHODS: In 80 patients with viral hepatitis and cirrhosis, MR images including T2*-weighted gradient echo images (echo time > or = 6.5 ms) were reviewed. The grades of parenchymal iron deposition and iron-containing nodules in the liver and spleen and the liver-to-muscle and spleen-to-muscle signal intensity ratios were compared with the most recent, the mean, the lowest, and the highest values from all available serum ferritin levels. RESULTS: The serum ferritin concentration was significantly correlated with the grades of iron deposition in liver and spleen and with the grades of iron-containing nodules seen on MR images (p < 0.05). Liver-to-muscle signal intensity ratio was weakly correlated with the ferritin concentrations. Among categories of ferritin concentration, correlation with MR grades was highest for mean ferritin concentration (r = 0.487, p < 0.001). CONCLUSION: MR imaging grades of hepatic iron and siderotic nodules correlate with serum ferritin, especially with the mean levels.

Adult↗
PubMedDate not supplied

Hepatic MR imaging: comparison of 2D and 3D gradient echo techniques.

BACKGROUND: To compare fat-suppressed three-dimensional gradient echo (3D-GRE) and two-dimensional gradient echo (2D-GRE) techniques for hepatic magnetic resonance imaging. METHODS: For 107 patients with suspected focal hepatic lesions, unenhanced 2D-GRE multislice in-phase and opposed-phase images and 3D-GRE images were obtained. Two radiologists independently and in random order reviewed the images. Quantitative analysis compared contrast-to-noise ratio (C/N) of liver masses and of the liver to spleen and signal-to-noise ratio (S/N) of the liver. Subjective grading of lesion conspicuity, confidence for lesion detection, artifacts, and overall image quality were also evaluated. RESULTS: Conspicuity and confidence for focal lesions was statistically significantly higher on 3D-GRE than on 2D-GRE images. Liver-to-spleen C/N was higher on 3D-GRE images than on in-phase and opposed-phase 2D-GRE images (p < 0.01). Liver S/N was higher on in-phase 2D-GRE images than on 3D-GRE and opposed-phase 2D-GRE images (p < 0.001). Lesion-to-liver C/N was higher on 3D-GRE images than on 2D-GRE images for nonsolid lesions (p < 0.05), but there was no significant difference for solid lesions. Motion and pulsation artifacts were significantly fewer on 3D-GRE images, but graininess and shading were significantly higher. Overall image quality was not significantly different for the three sequences. CONCLUSION: Fat-suppressed 3D-GRE sequences can afford comparable or better image quality than 2D-GRE images and may have the potential to detect more focal hepatic lesions.

Adult↗
PubMedDate not supplied

Giant hyperplasia of the caudate lobe of the cirrhotic liver: correlation with an anomaly of the caudate portal branch.

Different imaging appearances of giant hyperplastic change of the caudate lobe of the liver are presented in a patient with liver cirrhosis. The mass like caudate lobe was isoechoic on ultrasound, hypodense on postcontrast computed tomography (CT), hyperintense on T1-weighted magnetic resonance, images and isointense on T2-weighted images. These imaging findings are similar to those of dysplastic nodule in cirrhotic liver. The caudate lobe received normal portal flow on CT during arterial portography, but superior mesenteric arteriography showed precocious or early division of the caudate portal branch. We suspect that caudate hyperplastic change may be correlated to anomalous caudate portal vein branch.

Humans↗
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Budd-Chiari syndrome: hepatic venous obstruction by an elevated diaphragm.

We describe two cases of Budd-Chiari syndrome detected by magnetic resonance imaging that resulted from compression of the inferior vena cava by an elevated right hemidiaphragm. Magnetic resonance images demonstrated elevation of the right hemidiaphragm and medial deviation of the inferior vena cava with short segmental narrowing. The hepatic veins and inferior vena cava were patent but discontinuous. Hepatic venous drainage was assisted by multiple large intrahepatic collaterals.

Aged↗
PubMedDate not supplied

Gallbladder adenomyomatosis: findings on MRI.

BACKGROUND: To describe the characteristic magnetic resonance imaging (MRI) findings of gallbladder adenomyomatosis in two cases. METHODS: Two patients had abdominal MRI findings of gallbladder adenomyomatosis confirmed at cholecystectomy. RESULTS: The surgical specimen showed findings typical of adenomyomatosis, including marked thickening of both epithelial and muscular elements with multiple Rokitansky-Aschoff sinuses. On gadolinium-enhanced spoiled gradient-echo images and single-shot fast spin-echo images, mild gallbladder wall thickening with multiple intramural cystic components from Rokitansky-Aschoff sinuses were readily visualized. CONCLUSION: Adenomyomatosis of the gallbladder can be detected and diagnosed from MRI findings.

Aged↗
PubMedDate not supplied

Free MRA of the abdomen: postprocessing dynamic gadolinium-enhanced 3D axial MR images.

Dynamic contrast-enhanced whole-abdomen axial images were obtained by using a fat-suppressed, three-dimensional, breath-hold enhanced fast spoiled gradient-echo technique, configured for optimal evaluation for detection and characterization of liver lesions. We then evaluated the feasibility of using these images to reconstruct "free" abdominal magnetic resonance angiography, without additional cost or acquisition time, in 32 randomly chosen patients. The aorta, celiac trunk, superior mesenteric, hepatic, splenic, and renal arteries were clearly depicted.

Abdomen↗
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Femoral head avascular necrosis in sickle cell anemia: MR characteristics.

Since considerable expansion of hematopoietic marrow occurs in patients with sickle cell anemia (SCA), magnetic resonance images of 20 hips in 10 patients with known homozygous SCA were reviewed to determine a) if low signal hematopoietic marrow extended into the femoral capital epiphysis and b) if the MR characteristics of avascular necrosis (AVN) differed depending on the type of epiphyseal marrow. Our results revealed variable epiphyseal marrow type; mixed (fatty and hematopoietic) marrow (42%), fatty marrow (32%), hematopoietic marrow (16%) and hemosiderotic marrow (10%). AVN occurred irrespective of the underlying marrow. Segmental areas of low signal intensity in variable shapes (ring, band, crescent or large homogeneous area) was the most consistent MR manifestation of AVN in SCA. A low signal intensity peripheral rim surrounding a central zone, isointense with epiphyseal marrow on T1 and T2 weighted images, was most frequently observed similar to that described in patients without hemoglobinopathy. The notable difference, however, was of segmental areas within the same femoral head that demonstrated variable central zone signal on T2 weighted images. Further, while an increase in hip joint fluid is commonly seen with both early and advanced AVN in patients without hemoglobinopathy; it was increased in only one hip in patients with SCA. The observed differences in MR characteristics may be due to different pathophysiology of AVN in patients with SCA.

Adolescent↗
PubMedDate not supplied

Multiple spin-echo MR imaging of the body: image contrast and motion-induced artifact.

For a given TR and TE, image quality changes when the number of spin echoes obtained is varied. To investigate the importance of this in clinical imaging, a total of 4 patients and 9 volunteers had MRI examinations of the abdomen (n = 7) and/or pelvis (n = 8) which included at least 2 sequences with identical TR (2000 or 2500 ms), TE (80 ms) and other parameters, but with a different series of refocusing pulses. Sequences included single-echo (S), asymmetric and symmetric double-echo (AD and SD) and quadruple-echo (Q) techniques. Image contrast and severity of motion-induced artifact was measured via blind examination by 3 independent MRI radiologists and calculation of signal-difference, signal-difference-to-noise ratios and intensity of motion-induced "ghost artifact." The order of decreasing signal differences was S, SD, AD and Q, and all of three liver lesions were better seen with S than with SD techniques. These observations are consistent with signal loss from cumulative inaccuracies from multiple 180 degrees RF pulses. The order of increasing intensity of ghost artifact was Q, SD, AD and S, consistent with the beneficial motion artifact-reducing effects of even-echo rephasing. Knowledge of these effects of multi-echo imaging allows one to make informed decisions about imaging protocols rather than to simply obtain multiple echoes "because they are free."

Abdomen↗
PubMedDate not supplied

Induced renal artery stenosis in rabbits: magnetic resonance imaging, angiography, and radionuclide determination of blood volume and blood flow.

To investigate the ability of MRI to detect alterations due to renal ischemia, a rabbit renal artery stenosis (RAS) model was developed. Seven rabbits had RAS induced by surgically encircling the artery with a polyethylene band which had a lumen of 1 mm, 1 to 2 weeks prior to imaging. The stenosis was confirmed by angiography, and the rabbits were then imaged in a 1.4 T research MRI unit. T1 was calculated using four inversion recovery sequences with different inversion times. Renal blood flow, using 113Sn-microspheres, and regional water content by drying were then measured. The average T1 of the inner medulla was shorter for the ischemia (1574 msec) than for the contralateral kidney (1849 msec), while no change ws noted in the cortex. Ischemic kidneys had less distinct outer medullary zones on IR images with TI = 600 msec than did contralateral or control kidneys. Blood flow to both the cortex and medulla were markedly reduced in ischemic kidneys compared with contralateral kidneys (119.5 vs. 391 ml/min/100 gm for cortex and 19.8 vs. 50.8 ml/min/100 gm for medulla). Renal water and blood content were less affected. Our rabbit model of renal artery stenosis with MRI, radionuclide, and angiographic correlation has the potential to increase our understanding of MR imaging of the rabbit kidney.

Angiography↗