Assessment of acute myocardial infarction in man with magnetic resonance imaging and the use of a new paramagnetic contrast agent gadolinium-BOPTA.

To assess the feasibility of and characterize the new paramagnetic contrast agent gadolinium-BOPTA/dimeglumine (Gd-BOPTA) to detect acute myocardial infarctions with MR imaging, 24 patients (53.3 +/- 8.3 yr) were examined 9.3 +/- 3.6 days after a first myocardial infarction. Short-axis T1-weighted and T2-weighted MR imaging was performed at three slice levels. T1-weighted images were obtained before, immediately after, 15, 30, and 45 min after injection. Patients received either 0.05 or 0.1 mmol/kg body weight Gd-BOPTA. Images were qualitatively and quantitatively analyzed. Two patients showed no signs of infarction on T2-weighted images as opposed to contrast-enhanced T1-weighted images. Contrast-to-noise ratio was not affected by the dosage level. Signal intensity (SI) of normal to infarcted myocardium was significantly improved by both dosages (p < .0005) but a dosage of 0.05 mmol/kg produced significantly higher SI inf/norm (1.42 +/- 0.07 vs. 1.34 +/- 0.06, respectively, p = .015). SI of normal and infarcted myocardium enhanced immediately after administration of 0.05 mmol/kg (29.3 +/- 5.1% and 53.8 +/- 9.6% respectively), which decreased thereafter to 5.3 +/- 4.8% and 40.2 +/- 8.5% respectively, at 45 min (p < .002 for normal myocardium). SI enhancement immediately after 0.1 mmol/kg Gd-BOPTA showed no decrease within the first 45 min. Gd-BOPTA enables the detection of myocardial infarction. Optimal infarct delineation is achieved from 15 to 45 min after administration of 0.05 mmol/kg body weight Gd-BOPTA. Gd-BOPTA at 0.05 mmol/kg does improve image quality as measured by contrast-to-noise ratio and SI enhancement as compared to 0.10 mmol/kg.

Quantification of coronary artery bypass graft flow by magnetic resonance phase velocity mapping.

OBJECTIVES: Determination of the true coronary artery bypass graft function requires quantification of the flow rate within the graft. The purpose of the present study was to assess the feasibility of characterizing and quantifying graft flow by magnetic resonance phase velocity mapping. MATERIALS AND METHODS: Twenty-seven patients with 41 angiographically patent coronary artery bypass grafts underwent electrocardiographically gated magnetic resonance phase velocity mapping. Imaging was performed at 0.6 Tesla using a surface coil. Velocity maps of the bypass grafts were obtained throughout the cardiac cycle with a temporal resolution of 50 ms and a spatial resolution of 1.9 x 1.2 x 5 mm3, allowing calculation of phasic and mean graft flow. RESULTS: Adequate flow measurements were obtained in 84% (41 out of 49) of the grafts. Coronary artery bypass graft flow was characterized by a biphasic pattern with a first peak during systole and a second peak during diastole. Average maximum systolic and diastolic velocities over the cross-section of the grafts were 14 +/- 8 cm/s and 15 +/- 9 cm/s, respectively. Mean coronary artery bypass graft cross-sectional area was 0.28 +/- 0.13 cm2. Mean volume flow was 87 +/- 59 ml/min. CONCLUSION: Flow in coronary artery bypass grafts can be characterized and measured noninvasively by magnetic resonance phase velocity mapping.

The role of magnetic resonance in the evaluation of functional results after CABG/PTCA.

Magnetic resonance imaging (MRI) is a non-invasive modality which can be used for direct visualization of coronary artery bypass grafts. Spin-echo and gradient-echo (cine-MRI) techniques are now available on standard MR machines and provide information on graft morphology and graft patency with a 90% accuracy. By combining the standard techniques with MR phase velocity mapping, the flow rate in the graft can be measured, thereby offering a unique non-invasive assessment of the graft function. Newer techniques include MR coronary angiography, pharmacologically induced stress MRI, ultrafast MRI of the first-pass (perfusion) of a paramagnetic contrast agent through the myocardium, and 31P MR spectroscopy of high-energy phosphate metabolism of the myocardium. All of these may develop into valuable diagnostic tools for the assessment of functional results after CABG or PTCA, but still require clinical validation. At present, MRI is a useful screening procedure for assessment of graft patency and function in post-operative pain syndromes and in late graft occlusion or stenosis.

Selection of patients for resection of colorectal metastases to the liver using diagnostic laparoscopy and laparoscopic ultrasonography.

OBJECTIVE: To assess the value of diagnostic laparoscopy (DL) and laparoscopic ultrasonography (LUS) in the staging and selection of patients with colorectal liver metastasis. SUMMARY BACKGROUND DATA: Preoperative imaging modalities such as ultrasound, computed tomography, and magnetic resonance imaging are limited in the assessment of the number and exact location of hepatic metastases and in the detection of extrahepatic metastatic disease. Consequently, the surgeon is often faced with a discrepancy between preoperative imaging results and perioperative findings, resulting in either a different resection than planned or no resection at all. METHODS: Fifty consecutive patients were planned for DL and LUS in a separate surgical sitting to assess the resectability of their liver metastases. All patients were considered to be candidates for resection on the basis of preoperative imaging studies. RESULTS: Laparoscopy could not be performed in 3 of the 50 patients because of dense adhesions. The remaining 47 patients underwent DL. On the basis of DL and LUS, 18 (38%) patients were ruled out as candidates for resection. Of the 29 patients who subsequently underwent open exploration and intraoperative ultrasonography, another 6 (13%) were deemed to have unresectable disease. CONCLUSIONS: The combination of DL and LUS significantly improves the selection of candidates for resection of colorectal liver metastases and effectively reduces the number of unnecessary laparotomies.

Value of magnetic resonance imaging in assessing patency and function of coronary artery bypass grafts. An angiographically controlled study.

BACKGROUND: Previous studies have demonstrated the high sensitivity and moderate specificity of standard magnetic resonance (MR) spin-echo (SE) and gradient-echo (GE) techniques in predicting the patency of coronary artery bypass grafts. These techniques, however, do not provide quantitative information. Therefore, the objectives of this study were first to investigate whether MR cine GE images, performed in addition to standard SE images, have additional value for the assessment of graft patency and second to assess the graft function by measuring the flow pattern and flow rate with MR phase velocity imaging. METHODS AND RESULTS: Forty-seven patients with previous histories of coronary artery bypass grafting underwent angiography and MR SE and cine GE phase velocity imaging. SE and GE images were evaluated by three independent observers blinded to the angiographic results. The spatial mean velocity and volume flow were measured and repeated for each image at consecutive 50-millisecond intervals throughout the cardiac cycle. The 47 patients had 98 proximal aortotomies, of which 60 were single and 38 sequential grafts. Seventy-three grafts were patent; 25 were occluded. Eighty-four grafts (86%) were eligible for comparison of the results of SE and GE images. Assessment of patency was inconclusive on SE images in 7 grafts (5 occluded by angiography) and on GE images in 7 grafts (2 occluded). A comparison of the results of contrast angiography and SE and GE MR imaging techniques showed that both techniques had a high sensitivity (both 98%) and somewhat lower specificity (85% and 88%, respectively) for graft patency. Combined analysis of the SE and GE images did not improve the accuracy. The strength of the interobserver agreement on GE images was good (kappa = 0.66), whereas on SE images the agreement was moderate (kappa = 0.51). Adequate MR phase velocity profiles were obtained in 62 (85%) of the 73 angiographically patent grafts. Graft flow was characterized by a balanced biphasic forward flow pattern. The volume flow of sequential grafts to 3 regions (136 +/- 106 mL/min) was significantly higher than in single grafts (63 +/- 41 mL/min, P < .01). CONCLUSIONS: Considering the good interobserver agreement and the 85% success rate of quantitative flow measurements, cine GE phase velocity mapping is a promising clinical tool in the noninvasive assessment of graft patency and function.