Magnetic Resonance Imaging (MRI)

The authors developed and evaluated a polymer as a contrast agent for magnetic resonance (MR) angiography. The agent consists of a monomethoxy ether of poly(ethylene glycol) covalently attached to poly(L-lysine) (PL), with PL serving as the carrier of gadolinium diethylenetriaminepentaacetic acid (DTPA). Immunogenicity and toxicity studies were performed in mice, and biokinetic and metabolic studies were performed in rats. Dose response studies were performed with a three-dimensional time-of-flight sequence in eight rats.

Detection and quantification of flow of the left anterior descending (LAD) coronary artery in healthy volunteers are demonstrated using echo-planar imaging (EPI). A time-of-flight (TOF) model was used to derive coronary flow velocities from wash-in curves, free of cardiac wall motion contamination. Short-axis cardiac studies were performed using a gated, gradient echo EPI technique to limit the effect of cardiac wall motion on coronary vessel imaging. A series of 10 to 20 single or multislice images were acquired within a single breath-hold.

Three magnetopharmaceuticals based on a monocrystalline iron oxide nanocompound (MION) are evaluated as potential contrast agents for demonstrating axonal transport in vivo by magnetic resonance (MR) imaging. One agent has a strong positive charge, one has a strong negative charge, and the third is covalently linked to wheat germ agglutinin, a plant lectin with a high affinity for axon terminals. All three agents were tagged with rhodamine, and fluorescence microscopy was used to determine their fate after administration and to validate the imaging results.

The measurement of cardiac output and ejection fraction is useful in the treatment of diverse cardiac and cardiopulmonary disease states. Although several techniques are available for accurate measurement of left ventricular parameters, assessment of the right ventricle is less well represented. No single method is overwhelmingly superior, each having different strengths and weaknesses.

OBJECTIVE: We hypothesized that the previously observed T1 effect of a small monocrystalline iron oxide preparation can be exploited to decrease T1 relaxation time of blood. Such a decrease, particularly if present for a long time, could be used to improve the quality of MR angiograms. To test the hypothesis, we performed phantom studies and in vivo animal experiments.

The myocardial MR signal reduction associated with an intravenous bolus of Gd-DTPA and Dy-DTPA was studied in a canine model. Imaging was performed with a high speed echo-planar type imaging system (Instascan, Advanced NMR Systems, Inc.). Gated spin-echo images were obtained with TE of 30 ms, which permits image acquisition in approximately 40 ms. The gated TR was dependent on the heart rate, with an average TR of 2.4 s. After 0.1 mmol/kg of contrast was injected, 70 images were acquired, which showed in an 80-image data set a reduction in myocardial signal with a gradual return to normal.

PURPOSE: To investigate the utility of a monocrystalline iron oxide nanoparticle (MION) as a contrast agent in magnetic resonance (MR) imaging of lymph nodes.
MATERIALS AND METHODS: Pharmacokinetic data were obtained in rats after intravenous, subcutaneous, and intraarterial injection of indium-111-MION-46. MR imaging was performed to determine optimal dosages and pulse sequences in rats. Models of lymph node metastasis in rabbits and lymph node hyperplasia in rats were used to demonstrate the efficacy of MION in differentiation of malignant and benign adenopathies.

To develop guidelines for clinical magnetic resonance imaging of the liver, the authors undertook an animal study to investigate the effect of dose and pulse sequence on liver signal intensity in gadopentetate dimeglumine-enhanced echo-planar imaging. Serial imaging of the liver was performed in anesthetized rats after intravenous administration of five different doses (0.01, 0.05, 0.1, 0.2, and 0.5 mmol/kg) of contrast agent, with six different pulse sequences.

OBJECTIVE: A macromolecular MR contrast agent (MPEG-PL-GdDTPA), which consists of Gd-DTPA covalently attached to a polyamino acid (PL) derivatized by monomethoxy ether of polyethylene glycol (MPEG), has recently been developed. This contrast agent exhibits long intravascular retention, which makes it suitable for MR angiography. The current study was performed to test whether this agent would improve visualization of the pulmonary vasculature during MR angiography and whether it aids in the detection of pulmonary emboli in an animal model.

OBJECTIVE: Echoplanar MRI (EPI) with data acquisition times as short as 36 ms has been advocated for imaging body areas where gross physiologic motion degrades images. In this study we investigated the effect of various operator-defined parameters on image quality in EPI of the abdomen using a commercially available scanner.