Magnetic Resonance Imaging (MRI)

A new approach for producing primarily T2- and proton-density-weighted MR images in less time than the conventional long TR, long TE imaging is to reduce the TR of a double spin-echo pulse sequence and to also reduce the RF excitation flip angle to minimize the resulting T1 sensitivity.

A rat model of cerebral hemorrhage using stereotaxic injection of blood into the right basal ganglia was developed to investigate the influence of iron metabolism on the appearance of cerebral hemorrhage on MR images. Images of in vitro fixed brain sections stained specifically for different iron-storage substances, ferritin and hemosiderin, created by digitization of the pathology sections using an Eikonix CCD camera, were compared with the in vivo MR images of late-phase hematomas. Areas of the pathologic and MR features of the lesions were quantitatively correlated.

A rat model of cerebral hemorrhage using stereotaxic injection of blood into the right basal ganglia was developed to investigate the influence of iron metabolism on the appearance of cerebral hemorrhage on MR images. Images of in vitro fixed brain sections stained specifically for different iron-storage substances, ferritin and hemosiderin, created by digitization of the pathology sections using an Eikonix CCD camera, were compared with the in vivo MR images of late-phase hematomas. Areas of the pathologic and MR features of the lesions were quantitatively correlated.

An ultrasmall superparamagnetic iron oxide (USPIO) preparation was evaluated as a potential intravenous contrast agent for lymph nodes. Relaxation time measurements and magnetic resonance (MR) imaging were performed in rats with normal lymph nodes and in rats with lymph node metastases. In normal animals, lymph node relaxation times decreased maximally within 24-48 hours after intravenous administration of USPIO.

Knowledge of regional hemodynamics has widespread application for both physiological research and clinical assessment. Here we review the use of MR contrast agents to measure tissue perfusion. Two primary mechanisms of image contrast are discussed: relaxivity and susceptibility effects. Relaxivity effects result from dipolar enhancement of T1 and T2 rates. Because tissue T1 rates are intrinsically smaller, the dominant effect is shortening of T1 relaxation times.

Magnetic resonance diffusion imaging reflects the water mobility at each point in a tomographic image. We have studied brain water diffusion in 18 normal volunteers to identify the different factors that can influence diffusion measurements in vivo. Our results show that both the measurement accuracy and the measured diffusion coefficient strongly depend on the experimental parameters, in particular, echo and diffusion time, cardiac gating, and diffusion encoding gradient direction.

Previously we have reported that ultrasmall superparamagnetic iron oxide (USPIO) particles migrate across capillary endothelium, a prerequisite for the design of particulate pharmaceuticals for MR receptor imaging. In the current study, USPIO particles are directed specifically to asialoglycoprotein (ASG) receptors by coupling galactose terminals in the form of arabinogalactan (AG) to these particles. Biodistribution data showed that ASG-directed, AG-coated USPIO (AG-USPIO) particles selectively accumulate in the liver but not in other organs.

A new contrast agent for magnetic resonance (MR) imaging, directed to asialoglycoprotein (ASG) receptors on hepatocytes, was used for detection of liver cancer in rats. Ultrasmall superparamagnetic (mean size, 12 nm) particles of iron oxide (USPIOs) were targeted to ASG receptors by coating particles with arabinogalactan (AG). Liver T2 relaxation times decreased more effectively after a single intravenous administration of AG-USPIO than after an equal dose of a conventional superparamagnetic liver MR contrast agent (AMI-25; mean size, 72 nm).

The detection of serial changes in magnetic resonance (MR) signal intensity of the heart following acute myocardial infarction may provide a useful method of characterizing tissue healing. Fourteen patients with acute Q-wave infarction underwent T2-weighted, spin-echo cardiac imaging during hospitalization, followed by one or more additional MR studies (total 31) over a 6- to 27-wk period (mean: 3 mo).

To determine whether iron(III)ethylenebis-(2-hydrophenylglycine) (Fe-EHPG), a prototype hepatobiliary magnetic resonance imaging agent, can enhance the liver-to-tumor contrast-to-noise ratio (C/N) in models of liver tumors in mice, two types of cell inoculation were used: intrahepatic implantation of M5076 sarcoma and intrasplenic injection of colon tumor (C-26) or M5076 sarcoma. Significant enhancement of the liver-to-tumor C/N and/or improved visualization of small lesions was consistently observed on T1-weighted images obtained after injection of the contrast material.