T1 efficacy of EVP-ABD: a potential manganese-based MR contrast agent for hepatic vascular and tissue phase imaging

Manganese-enhanced magnetic resonance imaging (MEMRI)

The use of manganese ions (Mn(2+)) as an MRI contrast agent was introduced over 20 years ago in studies of Mn(2+) toxicity in anesthetized rats (1). Manganese-enhanced MRI (MEMRI) evolved in the late nineties when Koretsky and associates pioneered the use of MEMRI for brain activity measurements (2) as well as neuronal tract tracing (3). Currently, MEMRI has three primary applications in biological systems: (1) contrast enhancement for anatomical detail, (2) activity-dependent assessment and (3) tracing of neuronal connections or tract tracing. MEMRI relies upon the following three main properties of Mn(2+): (1) it is a paramagnetic ion that shortens the spin lattice relaxation time constant (T(1)) of tissues, where it accumulates and hence functions as an excellent T(1) contrast agent; (2) it is a calcium (Ca(2+)) analog that can enter excitable cells, such as neurons and cardiac cells via voltage-gated Ca(2+) channels; and (3) once in the cells Mn(2+) can be transported along axons by microtubule-dependent axonal transport and can also cross synapses trans-synaptically to neighboring neurons. This chapter will emphasize the methodological approaches towards the use of MEMRI in biological systems.

EVP-ABD-enhanced MRI to evaluate diffuse liver disease in a rat model

PURPOSE

To evaluate the feasibility of using manganese-based MR imaging contrast agent EVP-ABD to detect diffuse liver disease in an established rat hepatitis model.

MATERIALS AND METHODS

Hepatitis was induced by administration of CCl(4) in corn oil vehicle to rats intraperitoneally. MR images were acquired on a 3T scanner using a volume coil approximately 36 hours after the administration of CCl(4). EVP-ABD was administered via a tail vein at a dose of 10 mumol/kg. Multi-TI turboflash images were acquired to evaluate liver R1 (=1/T1) values before and after the EVP-ABD administration. Eighteen rats received various doses of CCl(4) and completed pre- and postcontrast MRI scans and liver histologic evaluation.

RESULTS

The liver R1 after the EVP-ABD administration and the change of the liver R1 before and after the administration, DeltaR1, show significant correlations with the CCl(4) dose. A significant correlation was also found between the histologic scores and the CCl(4) doses despite known variability in the relationship of CCl(4) dose to histology. A significant correlation was found between the histologic score and DeltaR1.

CONCLUSION

Our results indicate that EVP-ABD-enhanced MRI can detect diffuse liver disease generated by CCl(4) based on the significant correlation between proton R1 in liver following EVP-ABD and the CCl(4) doses as well as the histologic scores.

Manganese-calcium interactions with contrast media for cardiac magnetic resonance imaging: a study of manganese chloride supplemented with calcium gluconate in isolated Guinea pig hearts

OBJECTIVES

Manganese ions (Mn) enter cardiomyocytes via calcium (Ca) channels and enhance relaxation intracellularly. To prevent negative inotropy, new Mn-releasing contrast agents have been supplemented with high Ca. The study aim was to investigate how this affects cardiac function and magnetic resonance efficacy.

MATERIALS AND METHODS

MnCl2 based contrast agents, manganese and manganese-calcium (Ca:Mn 10:1), were infused during 4 repeated washin-washout sequences in perfused guinea pig hearts. [Mn] were 10, 50, 100 and 500 microM.

RESULTS

During washin, manganese depressed left ventricular developed pressure (LVDP) by 4, 9, 17, and 53% whereas manganese-calcium increased LVDP by 13, 18, 25, and 56%. After experiments, tissue Mn contents (nmol/g dry wt) were control <40, manganese 3720, and manganese-calcium 1620. T1 was reduced by 85-92% in Mn-enriched hearts.

CONCLUSIONS

High Ca supplements to Mn-releasing contrast agents may be counterproductive by inducing a strong positive inotropic response and by reducing the magnetic resonance efficacy.

MR Imaging of the Stomach: Potential Use for Mangafodipir Trisodium— A Study in Swine

PURPOSE

To evaluate mangafodipir trisodium as a potential contrast agent at magnetic resonance (MR) imaging of the stomach.

MATERIALS AND METHODS

Mangafodipir trisodium was injected intravenously into three swine at a dose of 5 micromol per kilogram of body weight. For comparison, gadopentetate dimeglumine was injected into three other swine at a dose of 0.1 mmol per kilogram of body weight. T1-weighted three-dimensional MR images were acquired in all six swine at 1.5 T before and approximately 10, 15, 20, 25, 30, and 40 minutes after contrast material administration. Extracted stomach specimens were imaged at 3.0 T. In vivo and ex vivo images were evaluated visually and quantitatively for contrast enhancement of the stomach, and in vivo images were evaluated for the presence of reflux from the duodenum.

RESULTS

Mangafodipir trisodium produced prolonged and selective enhancement of the inner surface of the stomach, in contrast to the more general enhancement seen with gadopentetate dimeglumine, and reflux from the duodenum could not account for this selective enhancement. Ex vivo images confirmed that T1 enhancement in the stomach wall with mangafodipir trisodium was limited to the inner surface. Gadopentetate dimeglumine did not produce selective enhancement of the inner surface of the stomach.

CONCLUSION

Mangafodipir trisodium preferentially enhances the inner surface of the stomach on MR images acquired in swine and, therefore, may have potential for use as a contrast agent at MR imaging of the human stomach.

Preliminary Evaluation of EVP 1001-1

RATIONALE AND OBJECTIVES

To investigate the potential of a novel manganese-based magnetic resonance (MR) contrast agent, EVP 1001-1 for the evaluation of myocardial ischemia.

METHODS

MR imaging with EVP 1001-1 was performed on 6 Yorkshire pigs, and T1 relaxation times were calculated. One animal served as a control, 2 were subjected to an acute coronary artery occlusion and 3 provided a model of chronic ischemia.

RESULTS

Administration of the agent in the control and acute coronary occlusion model demonstrated a short plasma half-life (approximately 1.5 minutes) and rapid myocardial uptake in nonoccluded regions, with long retention times in the myocardium (>1 hour) and no evidence of redistribution. In the chronic ischemia model, differential enhancement was observed between normal and ischemic tissue, particularly under dobutamine-induced stress.

CONCLUSIONS

These properties suggest the use of EVP 1001-1 for steady-state imaging of myocardial perfusion. Contrast administration could be performed under stress conditions outside the scanner, with high-resolution MR images reflecting the stress condition acquired after the stress has subsided.