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D D Stark

Publications and source records attributed to D D Stark.

At least 55 records · Page 3Linked to original sources
PubMed1989

Detection of hepatic metastases with MR imaging: spin-echo vs phase-contrast pulse sequences at 0.6 T.

The purpose of this study was to compare the sensitivity of T1-weighted and T2-weighted spin-echo (SE) pulse sequences with T2-weighted phase-contrast (PC) imaging techniques for the detection of hepatic metastases. Pulse-sequences performance was evaluated in 52 consecutive patients with 88 hepatic metastases who underwent MR imaging at 0.6 T. Lesion-liver contrast-to-noise ratios (CNR) on SE 260/14 (-12.4 +/- 6.7) and PC 2350/60 (+10.8 +/- 4.2) images were significantly (p less than .05) greater than on SE 2350/60 (+ 7.8 +/- 3.9), SE 2350/120 (+8.1 +/- 4.8), SE 2350/180 (+7.9 +/- 4.5), and PC 2350/30 (+4.6 +/- 2.9) images. Sensitivity for detection of 88 individual metastases was comparable on SE 260/14 (78 of 88 patients) and PC 2350/60 (81 of 88 patients) images and was significantly (p less than .05) greater than on in-phase T2-weighted SE images (TE = 60, 70 of 88 patients; TE = 120, 69 of 88 patients; TE = 180, 65 of 88 patients). Histologic analysis of tumor-free liver showed fatty change in 11 of 13 specimens available for pathologic evaluation. In all 11 of those patients, PC images increased tumor-liver contrast in comparison with the in-phase SE images. This analysis suggests that for detection of hepatic metastases at midfield strengths, the T1-weighted, short TR/short TE (SE 260/14) and the T2-weighted, phase-contrast (PC 2350/60) pulse sequences offer comparable performance.

Adult↗
PubMed1989

Magnetic resonance imaging of liver tumors.

Careful optimization of scanning techniques, particularly motion artifact suppression, has been essential to achieve reproducible results in abdominal MRI. The investigators experience indicates that MRI can be more accurate than other imaging methods for the detection of focal liver lesions. Furthermore, MRI is able to solve the major clinical problems in differential diagnosis of benign and malignant liver lesions: cancer v cavernous hemangioma or focal fat. MRI has reduced the dependence on liver biopsy and angiography to diagnose and stage focal liver lesions. Unfortunately, both imaging techniques, especially motion artifact suppression methods, vary widely among machines operating at different field strengths. Therefore, as hardware and software evolve, it is necessary to retrace the steps of pulse sequence optimization and clinical testing. Hopefully, in the future, standardized imaging techniques will become available for body MRI.

Adenoma, Bile Duct↗
PubMed1988

Splenic lymphoma: ferrite-enhanced MR imaging in rats.

Ferrite, a new magnetic resonance (MR) contrast agent, was evaluated in the detection and diagnosis of splenic lymphoma. Before administration of ferrite, normal rat spleens and spleens with diffuse lymphoma showed similar in vitro relaxation times and in vivo MR imaging signal-to-noise ratios (S/N). After the administration of ferrite (50 mumol Fe/kg), the T2 time of lymphomatous spleen was 27.0 msec +/- 2.9 (mean +/- standard deviation), which was significantly greater than that of normal spleen (10.7 msec +/- 1.5, P less than .005). The S/N of ferrite-enhanced in vivo MR images of lymphomatous spleen was 12.4 +/- 0.9, which was significantly greater than normal (5.7 +/- 0.2, P less than .005). Similar experiments with animal models of micronodular lymphoma also demonstrated that ferrite-enhanced MR imaging can distinguish micronodular lymphoma from normal spleen. Benign splenomegaly, studied with an animal model of erythroid hyperplasia, showed ferrite-enhanced MR tissue characteristics that were indistinguishable from those of normal spleen.

Animals↗
PubMed1988

Gd-DOTA: characterization of a new paramagnetic complex.

The relaxivity, biodistribution, and toxicity of the gadolinium-tetraazacyclododecanetetraacetic acid (Gd-DOTA) complex were evaluated. This cyclic complex has much greater in vitro stability (10(28)) than similar noncyclic complexes such as gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) (10(23)) or gadolinium-ethylenediaminetetraacetic acid (Gd-EDTA) (10(17)). The T1 relaxivity of Gd-DOTA (meglumine salt) determined in saline and in liver tissue at 20 MHz was similar to the relaxivity of Gd-DTPA. Tissue proton relaxation enhancement (PRE) correlated closely with chemical measurement of tissue gadolinium concentration. In rats, the biodistribution of Gd-DOTA was similar to Gd-DTPA with a distribution half-life of 3 minutes and an elimination half-life of 18 minutes. The median lethal dose (LD50) in mice of Gd-DOTA was 93% higher than that of Gd-DTPA; the calculated safety factor (ratio of LD50 to effective dose) was 53 for Gd-DOTA and 28 for Gd-DTPA. The data suggest that in vitro stability correlates with in vivo safety.

Animals↗
PubMed1988

Hepatic micrometastases in the rat: ferrite-enhanced MR imaging.

A rat tumor model was used to evaluate the ability of ferrite-enhanced magnetic resonance (MR) imaging to demonstrate hepatic metastases smaller than 1 cm. Twenty-eight rat livers were inoculated with 5 X 10(5) mammary carcinoma cells and imaged with a 0.6-T MR system. Non-enhanced and ferrite-enhanced images were analyzed and correlated with autopsy findings for each rat. Lesion detection rates correlated closely with cancer-to-liver contrast-to-noise ratios. Ferrite-enhanced MR imaging demonstrated significantly more lesions than non-enhanced imaging (P less than .05) and decreased the threshold size for lesion detectability (less than 2 mm). Ferrite also enabled more accurate measurements of the lesions (r = .96).

Animals↗
PubMed1988

Superparamagnetic iron oxide: clinical application as a contrast agent for MR imaging of the liver.

Superparamagnetic iron oxide (ferrite) particles were evaluated as a contrast agent for magnetic resonance (MR) imaging. In this pilot study, doses ranging from 10 to 50 mumol/kg were administered intravenously to 15 patients. Ferrite-enhanced images of the liver obtained with standard pulse sequence techniques significantly increased the number of hepatic lesions detected (P less than .01) and reduced the threshold size for detection to 3 mm (P less than .01). The improved clinical performance of ferrite-enhanced images correlated with significant increases in measured contrast-to-noise ratios (P less than .01). Degradation of superparamagnetic activity and/or clearance of ferrite from the liver was demonstrated as early as 12 hours after injection, suggesting that the lack of chronic toxicity observed in animal studies may be reproduced in humans. These initial clinical results appear to confirm extensive preclinical data indicating that ferrite administered at a dose of 20 mumol/kg has the potential to significantly improve the performance of abdominal MR imaging.

Adult↗
PubMed1988

Superparamagnetic iron oxide: enhanced detection of focal splenic tumors with MR imaging.

Superparamagnetic iron oxide (AMI-25), a reticuloendothelial cell-specific contrast agent for magnetic resonance (MR) imaging, was evaluated for its ability to permit detection of splenic metastases in 18 patients. Superparamagnetic iron oxide, at a dose of 30 mumol of iron per kilogram, decreased the signal intensity of spleen from 19.5 +/- 4.8 to 3.1 +/- 2.2 (spin-echo sequence, repetition time msec/echo time msec = 1,500/42; P less than .05), without changing the signal intensity of tumor. As a result, the tumor-spleen contrast-to-noise ratio increased from 0.2 (tumor isointense relative to spleen) to 18.0 (tumor hyperintense relative to spleen). As a consequence of increased contrast, splenic tumors were detected in four of 18 patients (45 individual lesions; P less than .05), whereas nonenhanced MR imaging permitted detection of splenic lesions in only two of 18 patients (four individual lesions). Maximum tumor-spleen contrast was achieved within 60 minutes after intravenous administration. These initial clinical results indicate that MR imaging with superparamagnetic iron oxide may offer improved accuracy in the diagnosis of splenic tumors.

Adenocarcinoma↗
PubMed1988

Pyogenic liver abscess: contrast-enhanced MR imaging in rats.

MR imaging was used to evaluate experimentally induced pyogenic liver abscesses in an animal model. Rats were examined before and after IV administration of either gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA), ferrite particles, or both contrast agents together. Pyogenic liver abscesses appeared hypointense on T1-weighted images and hyperintense on T2-weighted images. Bolus administration of Gd-DTPA using a fast spin-echo sequence with repetition time of 250 msec and echo time of 20 msec (SE 250/20) showed transient selective enhancement of normal hepatic tissue and increased lesion conspicuity, quantitatively assessed by the contrast-to-noise ratio, which increased from -35.7 to -59.0. Delayed leakage of Gd-DTPA into the abscess center partially obscured small lesions at 30-60 min. Ferrite particles reduced the signal intensity of normal liver, and the abscess then appeared homogenously hyperintense. Applying the SE 500/32 sequence, the contrast-to-noise ratio increased from -1.2 to +74.0. Coordinated administration of both contrast agents showed a further increase in contrast to +94.0, with a hyperintense abscess rim surrounded by hypointense liver. Gd-DTPA increases abscess-liver contrast by rim enhancement of the abscess wall, and ferrite increases the abscess-liver contrast by selectively decreasing the signal intensity of surrounding normal liver. As a result of increased contrast-to-noise ratio, both contrast agents, alone or in combination, increase the conspicuity of hepatic abscesses.

Animals↗
PubMed1988

Dual-contrast MR imaging of liver cancer in rats.

MR contrast agents increase hepatic tumor conspicuity, as measured in terms of contrast-to-noise (C/N) ratios. With an animal model of hepatic metastases from breast cancer, IV administration of Gd-DTPA (0.2 mmol/kg) shows a biphasic time response, transiently increasing the signal intensity of liver relative to tumor, with C/N ratio magnitudes increasing from -5.7 to -16.3 (SE 250/20); after a delay, the signal intensity of tumor increases relative to liver with a reversal of the C/N sign from negative to positive and an increase in the C/N magnitude to +25.0. IV administration of ferrite particles (0.05 mmol Fe/kg) shows a monophasic time response, increasing signal intensity of tumor relative to liver from +1.5 to +49.5 (SE 500/30). When both contrast agents were administered together (dual-contrast technique), the tumor-liver C/N magnitude reached a maximum of +67.8 (SE 500/30) 12 min after drug infusion. Analysis of individual contrast and noise factors contributing to this technique revealed a strong correlation between the signal intensity of liver and the signal intensity of ghost artifacts, which increase after administration of Gd-DTPA (r = .89) and decrease after administration of ferrite (r = 1.0). Dual-contrast imaging shows a synergistic addition of contrast and suppression of noise from ghost artifacts, maximizing the C/N and increasing the conspicuity of focal liver lesions.

Animals↗
PubMed1988

MR imaging of focal splenic tumors.

This study was undertaken to define the MR appearance of splenic tumors in 16 cancer patients with focal splenic lesions; 50 volunteers and liver cancer patients without splenic abnormalities served as controls. In 14 patients with focal splenic lesions, differences between splenic and lesion signal intensities permitted detection of splenic lesions on MR images, either because of cystic or necrotic areas lengthening T2 within the tumor, because of T1 shortening from tumor-associated hemorrhage, or because of T2 shortening of surrounding spleen in two cases of suspected transfusional iron overload. In one spleen, a lesion appeared isointense on both T1- and T2-weighted pulse sequences and was detected only by gross splenic deformity. In one other case, CT defined splenic metastases not visible on MR images. Measurements of signal intensity of normal spleens and tumor are so similar that spin-echo MR imaging can underestimate the size and extent of focal splenic disease or may miss lesions entirely. We conclude that MR imaging is a less sensitive technique for detecting focal lesions of the spleen than for detecting focal hepatic lesions.

Adult↗
PubMed1988

Differentiation of hepatic metastases from hepatic hemangiomas and cysts by using MR imaging.

T1-weighted and T2-weighted pulse sequences were employed for MR imaging of hepatic metastatic tumors (98 patients), hemangiomas (24 patients), and cysts (seven patients); a 0.6-T superconducting magnet was used. In a retrospective study, signal intensity and morphology were used to establish criteria for differentiating metastases from hemangiomas and cysts. The signal intensity of the lesion alone failed to be an etiologic discriminator because over 96% of all masses had a signal intensity less than that of liver on T1-weighted sequences, and at least 90% had a signal intensity greater than that of liver on T2-weighted sequences. Morphologic features depicted on T2-weighted images were more specific than those depicted on T1-weighted images in differential diagnosis. Amorphous, target, and halo signs and a change in morphology were present only in metastatic disease, with a frequency of 45%, 27%, 13%, and 12%, respectively. Two other morphologic patterns--doughnut and lightbulb signs--were found to have overlapping causes. Overall, at least one of the specific signs was observed in 92% of patients with metastatic disease. These data suggest that T2-weighted pulse sequences are essential for discriminating between hepatic metastases and hepatic hemangiomas and cysts. MR imaging is a promising technique for distinguishing these lesions.

Cysts↗