Assessment of intracardiac shunts with gadolinium-enhanced ultrafast MR imaging.

Abstract

Dye dilutional techniques are widely accepted for the assessment of intracardiac shunts, but current techniques require arterial access or radioisotope injection. Ultrafast (less than 500 msec) magnetic resonance (MR) imaging is ideally suited for the evaluation of an indicator during passage through the heart. Twenty patients were studied, including 13 with shunts. Four-chamber, T1-weighted images were obtained during bolus injection of gadopentetate dimeglumine. A single image was obtained in 420 msec, with repetitive images acquired after each QRS complex. After the contrast material was injected, there was pronounced signal intensity enhancement in the right atrium, followed by the right ventricular cavity, left atrium, left ventricular cavity, and descending aorta. Patients with substantial intracardiac shunts demonstrated early recirculation. First-pass contrast material-enhanced MR imaging is a promising new technique for the rapid assessment of intracardiac shunts. Combined with anatomic and functional MR imaging techniques, it can help provide a comprehensive noninvasive evaluation of suspected intracardiac shunts or provide follow-up in patients with known shunts.

Magnetic Resonance Image-Guided Transcatheter Closure of Atrial Septal Defects

“…ASD balloon sizing was then performed with an Amplatzer sizing balloon as described elsewhere. 11,12 After the study, the animals were observed for 12 hours in a postoperative care unit.…”

“…For better visualization of the atrial anatomy and the shunt, a fast T1-weighted gradient-echo sequence was used for MR angiography after a bolus administration of 10 mL of gadolinium-gadopentetate dimeglumine (Magnevist, Berlex). 12 The size of the defect was determined by using orthogonal short-and long-axis single-shot and cine-images. These measurements were repeated for the same slice position with an antenna guide wire (Surgi-Vision, Inc) crossing the ASD, which allows for a smaller field-of-view (FOV) without causing aliasing artifacts, and with the conventional external phase array coils turned off.…”

Assessment of myocardial perfusion by magnetic resonance imaging

“…Secondly, linearity between signal intensity and myocardial gadolinium-DTPAconcentration has only been reported in vitro for a concentration of < 2 mmol/1 [5,26,56]. Other influencing factors are: regional blood volume, the size of the extracellular space, permeability of the endothelium, and the water-proton exchange between different compartments.…”

Cardiovascular Magnetic Resonance: Myocardial Perfusion

“…While gadolinium-DTPA is extremely well-tolerated with very few mild adverse effects [33,47,54], it is an extracellular agent that leaks out of the vascular bed rapidly (approximately 30 to 50% during the first pass) [75]. Linearity between the signal intensity and the concentration of gadolinium is only maintained at very low concentrations of less than 1.3 to 2.0 mmol/l [7,9,44,69,83,85].…”

“…Unfortunately, for MR perfusion measurements these requirements are not fulfilled with gadolinium-DTPA. The injection of the contrast agent via a peripheral vein leads to a slow and spread input curve [34], the contrast agent diffuses rapidly from the intravascular into the interstitial space and remains there until complete clearance [74], and a linear correlation between tracer and signal intensity is only maintained at very low contrast agent concentrations [7,19,44,69,85]. Furthermore, with MR the effects of gadolinium-DTPA on proton relaxivity rather than the concentration of gadolinium-DTPA in the myocardium is detected making the acquired signal dependent on water exchange rates between the different compartments leading to a non-linear correlation between signal intensity and the concentration of the contrast agent.…”