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D D Stark

Publications and source records attributed to D D Stark.

At least 19 recordsLinked to original sources
PubMed1992

Clinical indications for MRI.

Safety considerations for MRI will continue to require careful attention and detailed scientific investigation. As new insights are gained into the hazards of time-varying electromagnetic and static magnetic fields, more sophisticated assessment of the true risk will be possible. At the present time, for established clinical indications, the risk of a mismanagement of disease appears to outweigh the minimal or unknown risks of MRI. Other than the mechanical hazards of implanted or external metallic or electrical devices, MRI seems to be an extraordinarily safe and compatible environment for patients undergoing evaluation of suspected diseases.

Humans↗
PubMed1992

Accumulation of iron oxide particles around liver metastases during MR imaging.

The histologic nature of the bright ring ("peritumoral edema") around some liver metastases on T2-weighted magnetic resonance (MR) images is controversial. In the case reported, particles of the iron oxide contrast agent AMI-25 are retained in the peritumoral zone of a colon cancer metastasis, causing the bright ring to disappear. The location of iron particles in resected specimens could be used systematically to study peritumoral edema.

Adenocarcinoma↗
PubMed1992

Magnetic resonance techniques and artifacts.

One area in which MR imaging can use improvement is the reduction of artifacts due to various physiologic motions during imaging. These artifacts degrade images and can cause misleading interpretations. This paper reviews some of the recent technical advances directed to remove these artifacts, as well as other techniques that improve MR imaging quality in general.

Artifacts↗
PubMed1991

Preclinical evaluation of MnDPDP: new paramagnetic hepatobiliary contrast agent for MR imaging.

Manganese(II)-N,N'-dipyridoxylethylenediamine-N,N'-diacetate-5,5'-bis (phosphate) (MnDPDP) is a paramagnetic complex designed for use as a hepatobiliary agent. The T1 relaxivity of MnDPDP (2.8 [mmol/L]-1.sec-1 in aqueous solution) was similar to that of gadolinium diethylenetriaminepentaacetic acid (DTPA) (4.5 [mmol/L]-1.sec-1) and gadolinium tetraazocyclodecanetetraacetic acid (DOTA) (3.8 [mmol/L]-1.sec-1). However, in liver tissue the T1 relaxivity of MnDPDP (21.7 [mmol/L]-1.sec-1) was threefold higher than that reported for Gd-DOTA (6.7 [mmol/L]-1.sec-1). Maximum liver T1 relaxation enhancement occurred 30 minutes after injection of MnDPDP, at which time 54MnDPDP biodistribution studies indicated that 13% of total body activity was in the liver. Enhanced (MnDPDP, 50 mumol/kg) MR images showed a fivefold increase in tumor-liver contrast-to-noise ratio over baseline unenhanced images. Results of the authors' acute and subchronic toxicity studies suggest that MnDPDP will be safe at the doses necessary for clinical imaging; at 10 mumol/kg, the safety factor (LD50/effective dose) for MnDPDP is 540, significantly greater than the safety factor of Gd-DTPA (ie, 60-100).

Animals↗
PubMed1991

Hepatobiliary MR imaging: first human experience with MnDPDP.

The first human MR imaging results for the hepatobiliary contrast agent manganese(II)N,N'-dipyridoxylethylenediamine-N,N'-diacetate 5,5'-bis(phosphate) (MnDPDP) are reported. MnDPDP is a paramagnetic contrast agent specific for hepatobiliary imaging. An imaging study was performed to investigate the presence of contrast enhancement or facilitated visualization of normal structures. Twelve healthy subjects receiving MnDPDP at doses of 3, 10, or 15 mumol/kg were imaged after injection for approximately 30 minutes at 1-5-minute intervals. Transaxial abdominal images were obtained at 1.5 T in a single breath-hold interval of 21 seconds with use of a spin-echo pulse sequence (repetition time = 150 msec, echo time = 20 msec). Liver parenchyma enhancement was observed 1 minute after injection and persisted for at least 30 minutes. Clearance into the gallbladder was visualized within 15 minutes. Enhancement was dose-dependent; a dose of 10 mumol/kg produced a 75%-100% signal enhancement of the liver at 10 minutes after injection.

Adult↗
PubMed1990

Clinical application of superparamagnetic iron oxide to MR imaging of tissue perfusion in vascular liver tumors.

Previous studies of AMI-25, a particulate iron oxide magnetic resonance contrast agent, imaged liver tumors 1 or more hours after injection, in the retention phase after complete clearance of AMI-25 from the circulation. In the present study, imaging was performed in the distribution phase, during the first 12 minutes after injection while contrast agent remain in circulation, and these images were compared with those obtained in the retention phase. Nineteen patients with cancer were studied, including 15 imaged during the distribution phase. T2-weighted distribution phase images demonstrated 90% of the lesions detected by means of T2-weighted retention phase images, showed a 3.5-fold increase in contrast-to-noise ratio over images obtained before administration of AMI-25, and increased diagnostic confidence by reducing signal from small intrahepatic blood vessels. Distribution phase images showed little contrast agent uptake by cancer tissue. Both distribution and retention phase images demonstrated greater contrast agent uptake by hemangiomas than by malignant neoplasms (P less than .01). The use of both distribution phase and retention phase AMI-25-enhanced images offers improved diagnostic accuracy in the detection and characterization of focal liver lesions.

Adenocarcinoma↗
PubMed1990

Hepatic cirrhosis and hepatitis: MR imaging enhanced with superparamagnetic iron oxide.

Superparamagnetic iron oxide was applied as a reticuloendothelial contrast agent in the diagnosis of cirrhosis and hepatitis in seven patients. Three patients had compensated cirrhosis, and four had active hepatitis. T1- and T2-weighted spin-echo magnetic resonance images were obtained before and 1 hour after the administration of iron oxide. Eight patients without diffuse liver disease served as a control group. Normal liver tissue showed a 75% +/- 9% reduction in signal intensity after the administration of iron oxide, and the liver appeared homogeneously hypointense. Cirrhotic liver tissue showed a smaller response (P less than .05) to iron oxide, with a 52% +/- 13% reduction in liver signal intensity. Inhomogeneous structures could be observed in enhanced images and are thought to represent fibrous bands or regenerating nodules. Liver tissue with active hepatitis showed a markedly reduced response to iron oxide (11% +/- 2%) (P less than .05), and the parenchyma appeared homogeneous. The authors conclude that the uptake of iron oxide particles is inhomogeneously altered in cirrhosis because of structural changes and homogeneously decreased in hepatitis because of functional changes of hepatic parenchyma.

Contrast Media↗
PubMed1990

First clinical trial of a new superparamagnetic iron oxide for use as an oral gastrointestinal contrast agent in MR imaging.

The authors report the results of preclinical testing and initial clinical application of a superparamagnetic iron oxide specifically prepared as a contrast agent for magnetic resonance (MR) imaging of the gastrointestinal tract. MR imaging was performed at 0.6 and 1.5 T in 15 volunteers. Images of the upper abdomen and pelvis were obtained before and after ingestion of the contrast material at doses of 22.5-225.0 mg of iron in 600-900 L. Two readers scored the images. Delivery of contrast material into the proximal and distal small bowel, with obvious loss of signal intensity (T2 enhancement), was achieved in all subjects. Enhanced images showed improved delineation of the head and tail of the pancreas, anterior margins of the kidneys, and paraaortic region. The contrast agent did not generate artifacts, an improvement over prototype formulations evaluated previously in animals. Except for a brief episode of diarrhea in five subjects, the agent was well tolerated. Use of this contrast agent improved the diagnostic quality of abdominal MR images by enabling the distinction of the bowel from nonbowel structures at concentrations that did not produce image distortion.

Adult↗
PubMed1990

Hepatic tumors: quantitative tissue characterization with MR imaging.

To determine which quantitative methods of image analysis are most suitable for the differential diagnosis of benign and malignant hepatic lesions, the authors analyzed magnetic resonance images obtained at 0.6 T in 42 patients with proved hepatic cavernous hemangioma and 63 patients with various hepatic malignancies. The lesion-liver signal-intensity ratio for images obtained with a repetition time of 2,350 msec and echo time of 180 msec was most helpful in distinguishing hemangiomas from cancer (area under the receiving operator characteristic curve [ROC] = 0.99 +/- 0.005). All 38 lesions with lesion-liver signal-intensity ratios greater than 3.5 were hemangiomas, whereas all 57 hepatic tumors with a ratio less than 2.5 were malignant neoplasms. A specificity of 93% and sensitivity of 89% can be achieved with use of quantitative signal-intensity data only. The authors conclude that in conjunction with heavily T2-weighted pulse sequences, signal-intensity ratios are an important adjunct to morphologic analysis in the differential diagnosis of hepatic neoplasms.

Adult↗
PubMed1990

Localization of P-31 MR signal with use of superparamagnetic iron oxide particles.

Volume localization of magnetic resonance signals was achieved by using the regional susceptibility differences produced by superparamagnetic iron oxide particles. In vitro experiments demonstrated a direct linear relationship between the concentration of particulate iron and phosphorus-31 chemical shift or line broadening. In vivo experiments indicated that an intravenous dose of 5-10 mg of iron per kilogram of body weight suppressed P-31 signal from normal liver in healthy rats. In rats with hepatic implants of mammary adenocarcinoma, superparamagnetic iron oxide particles suppressed detectable P-31 or hydrogen-1 signal arising from healthy liver tissue, but not that from tumor. Signal due to surface tissues, which affect surface-coil spectra, could be selectively suppressed with a film-based application of particles to the abdominal wall. Thus, P-31 spectra from simulated or actual lesions could be selectively detected after chemically suppressing signals from neighboring or surrounding tissue.

Adenosine Triphosphate↗
PubMed1990

Detection of hepatic metastases: comparison of contrast-enhanced CT, unenhanced MR imaging, and iron oxide-enhanced MR imaging.

Diagnostic accuracy of contrast-enhanced CT, unenhanced MR imaging, and MR images enhanced with superparamagnetic iron oxide was evaluated in 10 patients with histologically proved hepatic metastases. First, diagnostic performance of the imaging technique with respect to the ability of radiologists to recognize the presence or absence of a metastasis was measured by using receiver-operating-characteristic (ROC) analysis of single images. Second, the total number of lesions (N = 108) detected by "complete" CT and MR examinations was counted. Finally, lesion-liver contrast-to-noise ratios (CNR) were measured in all MR sequences. The area under the ROC curve was .67 +/- .03 for contrast-enhanced CT, .81 +/- .07 for the unenhanced SE 260/14 sequence, and .92 +/- .01 for the iron oxide-enhanced SE 1500/40 sequence. The enhanced SE 1500/40 sequence yielded significantly (p less than .005) greater accuracy than did contrast-enhanced CT. The same sequence detected significantly (p less than .05) more lesions than all other imaging techniques (19% more than the best unenhanced MR sequence and 36% more than contrast-enhanced CT). The enhanced SE 1500/40 sequence also yielded the highest CNR value (19.5 +/- 10.2) of all MR sequences. These results indicate that iron oxide-enhanced MR imaging is a superior imaging technique for the detection of hepatic lesions.

Adult↗
PubMed1990

Iron oxide-enhanced MR imaging of the liver and spleen: review of the first 5 years.

Superparamagnetic iron oxide (SPIO) particles are a potent new class of MR contrast agents affording improved detection of hepatic and splenic neoplasms. In this report we review the development of this agent through preclinical studies and early clinical results at Massachusetts General Hospital during a 5-year investigation. SPIO particles are sequestered by normal phagocytic Kupffer cells of the reticuloendothelial system (RES) but are not retained in tumor tissue. Consequently, there is a fivefold increase in T2 relaxation between normal RES tissue and tumor, with a comparable advantage in quantitative signal-to-noise ratio, contrast-to-noise ratio, and lesion detectability in the liver and spleen on MR imaging. Increased lesion conspicuity can be exploited to decrease threshold size for lesion detection to less than 3 mm. Clinically beneficial effects occur with a variety of mildly T2-weighted spin-echo pulse sequences; gradient-echo techniques show even greater benefit after administration of SPIO. Metabolically, pharmaceutical-grade preparations are biodegradable and bioavailable, being rapidly turned over into body iron stores and incorporated into erythrocyte hemoglobin. Early dose-escalation clinical trials have identified a probable clinical dose range of 10-20 mumols Fe/kg body weight. In the United States, SPIO compounds evaluated to date are still approved for use in investigational studies only. Newer commercial formulations currently being evaluated may extend clinical safety margins.

Animals↗