Heidi C. Schwickert

Angiographic properties of Gd-DTPA-24-cascade-polymer — a new macromolecular MR contrast agent

PURPOSE A new macromolecular MR contrast agent, Gd-DTPA-24-cascade-polymer, was assessed for MR angiography of peritumoral vessels in rats. MATERIAL AND METHODS High resolution 3D-SPGR (TR/TE 100/5ms, alpha = 90 degrees) angiograms were acquired in 10 Fischer rats bearing subcutaneous R3230 mammary adenocarcinomas. MRI was performed before, immediately and 40 min after administration of Gd-DTPA (0.1 mmol Gd/kg), and after either Gd-DTPA-cascade-polymer or albumin-(Gd-DTPA)30 (each 0.05 mmol Gd/kg). A semi-quantitative analysis of small peritumoral vessels and tumor rim enhancement was performed on maximum intensity projection (MIP) angiograms using a 4-point scoring system. A quantitative analysis compared vascular signal-to-background-(S/B), signal-to-noise-, and contrast-to-noise-ratio. RESULTS Gd-DTPA produced a transient and low-scoring vessel definition (0.2 +/- 0.1), but strong rim enhancement (score 1.7 +/- 0.1). The cascade polymer resulted in better but submaximal vessel delineation (score 1.6 +/- 0.3, S/B 5.0 +/- 0.2) and strong rim enhancement (score 1.8 +/- 0.1). Albumin-(Gd-DTPA)30 produced the best and most time-persistent angiograms (score 2.6 +/- 0.2, S/B 7.4 +/- 0.2), but minimal rim enhancement (score 0.3 +/- 0.2). CONCLUSIONS The Gd-DTPA-24-cascade-polymer demonstrated the useful combination of strong tumor rim enhancement and detailed angiographic definition of peritumoral vessels. These are advantages associated with extracellular and blood pool contrast media, respectively.

Tumor angiography using high-resolution, three-dimensional magnetic resonance imaging: Comparison of gadopentetate dimeglumine and a macromolecular blood-pool contrast agent

RATIONALE AND OBJECTIVES We compared the peritumoral vascular definition in rats using either a paramagnetic extracellular or a macromolecular contrast medium in combination with high-resolution magnetic resonance (MR) imaging. METHODS High-resolution, three-dimensional spoiled gradient-refocused acquisition in a steady state (SPGR) images were acquired from tumor-bearing Fischer-344 rats before, immediately after, and again 40 min after administration of gadopentetate dimeglumine (0.1 mmol Gd/kg; n = 10) and albumin-(Gd-DTPA)30 (0.05 mmol Gd/kg; n = 5). Small peritumoral vessels were analyzed semiquantitatively on maximum intensity projection angiograms using a 4-point scoring system; quantitative analyses included signal-to-background ratios (SBRs) and signal-to-noise ratios. RESULTS Gadopentetate dimeglumine caused a transient and low-scoring (0.2 +/- 0.1, SBR = 1.9 +/- 0.2) vessel definition but strong rim enhancement (score = 1.4 +/- 0.2). Albumin-(Gd-DTPA)30 produced persistent, high-quality angiograms (score = 2.6 +/- 0.2, SBR = 7.4 +/- 0.2) but minimal rim enhancement (score = 0.3 +/- 0.2). CONCLUSION Albumin-(Gd-DTPA)30 combined with high-resolution MR imaging produces time-persistent, detailed angiographic definition of peritumoral vessels. Vascular maps obtained with gadopentetate dimeglumine enhancement are not time persistent or of equal quality.

Contrast-enhanced MR imaging of two superparamagnetic RES-contrast agents: functional assessment of experimental radiation-induced liver injury.

The purpose of this study was to compare liver contrast‐enhancing characteristics of two superparamagnetic reticuloendothelial system (RES)‐directed agents with different particle sizes, polycrystalline iron oxide nanocompounds (PION) and carboxydextran‐coated maghemite (DDM128N/389, later referred to as DDM128), in an experimental model of focal radiation‐induced hepatitis. PION, for the small particle size (31 nm), and DDM128, for the large particle size (59 nm), RES‐directed agents were compared for liver enhancement after radiation‐induced liver injury. A single x‐irradiation exposure varying from 10 to 60 Gy was delivered to one side of the liver. T2‐weighted spin‐echo magnetic resonance imaging was performed 3 days after x‐irradiation at 30 minutes post‐contrast. Using the RES‐directed PION, the normal, non‐irradiated portion of the liver decreased in signal intensity with a maximum negative enhancement of −66%, while the irradiated portion of the liver decreased in signal intensity by −24% (60 Gy). The signal intensity decline of irradiated liver tissue using PION was dose dependent, but was found at all radiation dose levels (10–60 Gy). The difference in signal intensity between irradiated (−63%) and non‐irradiated (−82%) portions was also statistically different using DDM128 at 60 Gy. However, lower irradiation doses (10 and 30 Gy) failed to produce a statistically significantly different enhancement in the irradiated and non‐irradiated portion of the liver. Sensitivity of liver enhancement with RES‐directed agents is size dependent. The smaller particle (PION) is more sensitive for detection of radiation‐induced hepatitis than the larger particle (DDM128). The relative insensitivity of DDM128 enhancement for diffuse liver injury will be clinically advantageous for detecting focal lesions in the presence of diffuse hepatic injury.J. Magn. Reson. Imaging 1999;10:52–56.

Motility disorders of the esophagus: diagnosis with barium-rice administration.

PURPOSE To evaluate the role of barium-rice administration for a standardized diagnosis of dysphagia and esophageal motility disorders. MATERIALS AND METHODS Sixty healthy volunteers and 218 patients with various esophageal disorders (achalasia, scleroderma and other connective tissue diseases, neurologic diseases, esophagitis and others) were examined both by a conventional barium study and by a barium-rice study. The barium-rice meal consisted of barium sulfate and boiled rice, mixed half and half. The time required for esophageal clearance of one sip was measured. RESULTS Normal esophageal transit time in healthy controls was between 5 and 15 s for both methods. In patients, the conventional barium study revealed a prolonged transit time in only 16.5% (36 of the 218 cases). The barium-rice study was abnormal in 51.8% (113 of 218 cases), independent of the underlying disease. The barium-rice study was pathological in 77 of those 182 patients (42.3%) who had normal barium transit time. In 24 patients the radiologic results was confirmed by endoscopy and manometric measurements. CONCLUSIONS Esophageal motility abnormalities are detected by a barium-rice study with a high sensitivity. With this simple and low-cost method, quantitative and reproducible results can be obtained. Barium-rice administration is a suitable tool for screening and follow-up of patients with dysphagia and esophageal motility disorders.

MRI mapping of microvascular permeability and tissue blood volume

A quick and automated method for quantitative spatial mapping of tissue characteristics derived from contrast enhanced MR imaging by a macromolecular contrast medium (MMCM) was used in normal rats. Specifically, an established two compartment unidirectional flow kinetic model was automatically implemented on a pixel by pixel basis to calculate permeability surface area product (PS) and tissue fractional blood volume (BV) from MRI dynamic intensity data. The utility of PS and BV maps were evaluated in the normal rat abdomen where a range of fractional- BV was found: from 100% in the vena cava to 1% in skeletal muscles, with intermediate values for liver and kidney. Tissue permeability depicted on the PS maps was generally low for normal tissues.