Assessment of tissue edema in patients with acute myocardial infarction by computer-assisted quantification of triple inversion recovery prepared MRI of the myocardium.

The aim of this study was to design a computer algorithm to assess the extent of cardiac edema from triple inversion recovery MR images of the human left ventricular myocardium. Twenty-one patients presenting with acute myocardial infarction were scanned within 48 h of the onset of symptoms. Eight patients were scanned a second time, 4 weeks after the initial event. Myocardial edema was detected in 27 of 29 studies using visual contour-based manual segmentation. A reference standard, created from the segmentations of three raters by voxel-wise majority voting, was compared to the edema mass estimates obtained using a newly developed computer algorithm. At baseline (n=20), the reference standard yielded an edema mass of 16.4±15.0 g (mean±SD) and the computer algorithm edema mass was 16.4±12.6 g. At follow-up (n=7), the reference standard edema mass was 7.1±4.4 g compared to 16.3±7.7 g at baseline. Computer algorithm estimates showed the same pattern of change with 5.7±5.7 g at follow-up compared to 20.8±13.8 g at baseline. Although there was a significant degree of discrepancy between reference standard and computer algorithm estimates of edema mass in individual patients, their overall agreement was good, with intraclass correlation coefficient ICC(3, 1)=0.753.

Cerebral perfusion in infants and neonates: preliminary results obtained using dynamic susceptibility contrast enhanced magnetic resonance imaging.

BACKGROUND: Previous studies have used the dynamic susceptibility contrast enhanced (DSCE) magnetic resonance (MR) imaging technique to measure cerebral perfusion in adults. OBJECTIVE: To assess the feasibility of the technique in a heterogeneous cohort of sick human infants and identify cerebral perfusion abnormalities. METHODS: Perfusion measurements were made by characterising the changing concentration of an injected bolus of contrast agent using a series of MR images acquired during the first pass of the contrast bolus. Qualitative values of relative cerebral blood flow (rCBF) were then calculated from these data on a pixel by pixel basis to generate parametric maps of perfusion. RESULTS: Images of perfusion were successfully calculated from 12 out of 27 neonates and infants, all with established cerebral pathology. Normal vascular anatomical structures such as the circle of Willis were identified within all calculated images. Values of rCBF were generally larger in grey matter than in white matter. In several patients, perfusion abnormalities resulted in structural abnormalities which were detected in conventional MR imaging at follow up. The acquisition of perfusion data was most difficult when the least mature brains were examined because of motion artefacts and a smaller head size with a lower level of rCBF than adults. CONCLUSIONS: This preliminary study shows that: (a) maps of rCBF can be acquired from neonates and infants; (b) characterisation of the bolus passage becomes progressively easier as the brain matures; (c) early abnormalities in cerebral perfusion may have negative prognostic implications; (d) the main difficulty when using the DSCE technique to study neonates relates to image artefacts resulting from bulk head motion.

An observation of increased contrast due to both T1 and T2 weighting in a synthetic image.

An observation was made that subtracted images generated by an SR/IR interleaved pulse sequence on a low field strength magnetic resonance imager (M&D Technology Ltd, Aberdeen, Scotland) contained contrast between pathological and normal tissues that was not explained by either T1 or T2 weighting alone. A theoretical model for this image has been derived and its validity confirmed by phantom experiments. It is shown that the subtracted image is dependent on the product of T1 and T2 prolongation for contrast. This type of image might be of use in screening for unknown pathologies and such techniques may shorten routine patient imaging times.

Demonstration of pulsatile cerebrospinal-fluid flow using magnetic resonance phase imaging.

The study of pulsatile cerebrospinal-fluid (CSF) flow may be useful in diagnosis of certain forms of intracranial disease. Previous techniques used to study CSF flow either are invasive or do not allow accurate measurement. Magnetic resonance imaging (MRI) offers a non-invasive method of studying the CSF pathways. Our technique uses MR phase images and allows quantitative measurement of flow velocities and volume-flow rates. Four volunteers were studied at the level of the second cervical vertebra (C2). The MRI pulse sequence was gated from the R-wave of the subject's electrocardiogram and 12 scans were taken corresponding to different times in the cardiac cycle. The variation in flow velocity throughout the cycle was plotted, and maximum caudad and cephalad flow velocities and flow rates were calculated. Good agreement was found between three of the four volunteers. The mean maximum caudad velocity was 2.91 cm s-1 occurring at a mean time of 190 ms after the R-wave. This corresponds to a mean maximum flow rate of 4.13 ml s-1. The total imaging time for each study was about 1 h. Technical developments, allowing simultaneous acquisition of several images throughout the cardiac cycle, will reduce this time significantly.

Magnetic resonance imaging in the detection of focal liver lesions: comparison of dynamic contrast-enhanced TurboFLASH and T2 weighted spin echo images.

In a previous study using dynamic contrast-enhanced TurboFLASH (DCETF) for demonstration of the portal venous system we found that this technique showed more liver lesions than T2 weighted spin echo (T2WSE) imaging in the same patients. In this study we have formally compared axial T2WSE images (TR 2000, TE 45/90) with TurboFLASH images (TR 135, TE 4, FA 80 degrees) acquired immediately after bolus injection of Gd-DTPA (0.1 mmol kg-1) in 41 patients referred for hepatic magnetic resonance imaging (MRI) prior to surgery for liver lesions. The images of each sequence were independently reviewed by two observers. The lesions were counted and each sequence was scored for conspicuity, level of artefact and subjective image quality. Contrast-to-noise ratios using user defined regions of interest were calculated. Significantly more lesions were seen on DCETF (n = 186) images than on T2WSE (n = 123) images (p < 0.001). Lesion conspicuity was equal in 53% of cases, better on DCETF in 36% and better on T2WSE in 11%. Contrast-to-noise ratios were significantly higher on DCETF images (p < 0.05). DCETF imaging provided a substantial improvement in lesion detection compared with T2WSE imaging.

Magnetic resonance evaluation of the pericardium.

Magnetic resonance (MR) is well suited to imaging the pericardium. High resolution images synchronized with the cardiac cycle can be obtained in any plane. The wide field of view allows additional anatomical and functional information to be obtained from adjacent structures such as the aorta, pleura, lungs and mediastinum. MR is particularly useful in cases of pericardial constriction without an associated effusion, in patients with complex or loculated pericardial effusions and in pericardial tumours. In this article we illustrate the characteristic MR features of a variety of pericardial pathologies.

Fast magnetic resonance angiography using turbo-FLASH sequences in advanced aortoiliac disease.

A prospective study using contrast enhanced turbo-FLASH (Fast Low-Angle Shot) magnetic resonance (MR) angiography was performed to assess the arterial anatomy in patients who had advanced atherosclerotic aortoiliac disease. This new imaging sequence was employed in 17 patients and the results were compared with conventional abdominal aortography. MR angiography accurately detected all aortic occlusions (3/3), their sites and their extent. All nine iliac occlusions were correctly identified (sensitivity 100%, specificity of 90%). The sensitivity was 100% for stenosis of 50% or greater in the abdominal aorta, and the iliac and common femoral arteries. The degree of stenosis was overgraded in 20 of 51 lesions (39.2%). Mild stenosis was overgraded as moderate stenosis in 10 and as severe stenosis in three. Moderate stenosis was overgraded as severe stenosis in four. None of the mild or moderate stenoses resulted in areas of signal voids suggestive of occlusions. Three severe stenoses were seen as areas of signal voids (two iliac, one femoral). In the eight patients who had in total 10 aneurysmal dilatations of the aorta or the iliac arteries, MR angiography was superior in demonstrating the true extent of the aneurysms. We conclude that turbo-FLASH MR angiography has the potential to be a useful non-invasive imaging technique for patients with advanced aortoiliac disease.

Comparison of 99mTc tetrofosmin gated SPECT measurements of left ventricular volumes and ejection fraction with MRI over a wide range of values.

The calculation of ejection fraction using gated single photon emission computed tomography (SPECT) has been widely validated against a range of other techniques. There have been fewer studies validating left ventricular volumes. We compared quantitative gated SPECT (QGS) with magnetic resonance imaging (MRI) measurements of left ventricular ejection fraction and end diastolic volume in 50 patients with a large range of ventricular dimensions. MRI data were obtained using a turbo gradient echo pulse sequence (TGE) in 17 patients and a steady state free precession pulse sequence (SSFP) in 33 patients. There was good correlation between ejection fraction and end diastolic volume measurements from SPECT and MRI (r=0.82, r=0.90, respectively) but the mean SPECT values were significantly lower (ejection fraction, 6.6+/-6.4% points; end diastolic volume, 18.4+/-25.4 ml) than those obtained from MRI. Bland-Altman analysis showed some large differences in individual patients but no trends in the data either in ejection fraction over a range from 15% to 70% or in end diastolic volume, range 75-400 ml. SSFP gave a larger difference for end diastolic volume measurement compared to SPECT than did TGE, although this difference did not reach significance. Both SSFP and TGE gave similar values for the difference between MRI and SPECT for the measurement of ejection fraction. We suggest that the difference in EF may be a result of 8 frames being used for gating in QGS but 12-18 for MR. Differences in volumes may be related to the different spatial resolution and the exclusion or inclusion of trabeculation and papillary muscles between SPECT and MRI. Differences between SSFP and TGE may be caused by differing delineation of the endocardial border, dependent on the particular acquisition sequence. In conclusion, QGS values correlated well with MRI, but a correction factor may be needed if direct comparison is made.

Measurement of pharmacokinetic parameters in histologically graded invasive breast tumours using dynamic contrast-enhanced MRI.

Dynamic contrast-enhanced MRI (DCE-MRI) has demonstrated high sensitivity for detection of breast cancer. Analysis of correlation between quantitative DCE-MRI findings and prognostic factors (such as histological tumour grade) is important for defining the role of this technique in the diagnosis of breast cancer as well as the monitoring of neoadjuvant therapies. This paper presents a practical clinical application of a quantitative pharmacokinetic model to study histologically confirmed and graded invasive human breast tumours. The hypothesis is that, given a documented difference in capillary permeability between benign and malignant breast tumours, a relationship between permeability-related DCE-MRI parameters and tumour aggressiveness persists within invasive breast carcinomas. In addition, it was hypothesized that pharmacokinetic parameters may demonstrate stronger correlation with prognostic factors than the more conventional black-box techniques, so a comparison was undertaken. Significant correlations were found between pharmacokinetic and black-box parameters in 59 invasive breast carcinomas. However, statistically significant variation with tumour grade was demonstrated in only two permeability-related pharmacokinetic parameters: k(ep) (p<0.05) and K(trans) (p<0.05), using one-way analysis of variance. Parameters k(ep) and K(trans) were significantly higher in Grade 3 tumours than in low-grade tumours. None of the measured DCE-MRI parameters varied significantly between Grade 1 and Grade 2 tumours. Measurement of k(ep) and K(trans) might therefore be used to monitor the effectiveness of neoadjuvant treatment of high-grade invasive breast carcinomas, but is unlikely to demonstrate remission in low-grade tumours.

Safety and diagnostic accuracy of stress cardiac magnetic resonance imaging vs exercise tolerance testing early after acute ST elevation myocardial infarction.

OBJECTIVE: To determine the safety and diagnostic accuracy of adenosine-stress cardiac magnetic resonance (CMR) perfusion imaging early after acute ST elevation myocardial infarction (STEMI) compared with standard exercise tolerance testing (ETT). DESIGN AND SETTING: Cross sectional observational study in a university teaching hospital. PATIENTS: 35 patients admitted with first acute STEMI. INTERVENTIONS: All patients underwent a CMR imaging protocol which included rest and adenosine-stress perfusion, viability, and cardiac functional assessment. All patients also had an ETT (modified Bruce protocol) and x ray coronary angiography. MAIN OUTCOME MEASURES: Safety and diagnostic accuracy of adenosine-stress perfusion CMR vs ETT early after STEMI in identifying patients with significant coronary stenosis (>or=70%) and the need for coronary revascularisation. Also, to determine if CMR can distinguish between ischaemia in the peri-infarct zone and ischaemia in remote myocardium. RESULTS: CMR imaging was well tolerated (all patients completed the protocol) and no complications occurred. CMR was more sensitive (86% vs 48%, p = 0.0074) and more specific than ETT (100% vs 50%, p<0.0001) for detecting significant coronary stenosis, and more sensitive for predicting revascularisation (94% vs 56%, p = 0.039). Inducible ischaemia in the infarct related artery territory was seen in 21 of 35 patients and was associated with smaller infarct size and less transmurality of infarction. CONCLUSIONS: Adenosine-stress CMR imaging is safe early after acute STEMI and identifies patients with significant coronary stenosis more accurately than ETT.

A system for cardiac and respiratory gating of a magnetic resonance imager.

A cardiac and respiratory gating system is described which minimises MRI distortion by using a commercially available pneumatic capsule for respiration sensing, and by isolating the ECG and respiration detector circuitry with a fibre-optic link. Operator use is facilitated by displaying, on the ECG trace, the time during the cardiac cycle when images are acquired, and by displaying the respiratory signal. The system is presently in use with a MD 800 MRI system (M&D Technology Ltd, Aberdeen) operating at 0.08 tesla.

Bone marrow blood supply in gadolinium-enhanced magnetic resonance imaging.

A retrospective study was performed to determine whether bone blood supply can be assessed on gadolinium-enhanced magnetic resonance imaging. Lumbar spine magnetic resonance imaging (MRI) examinations of 49 patients attending for post-laminectomy examination were reviewed (30 male, 19 female, mean age 46.4 years, age range 23-84 years). Each study included sagittal T1-weighted spin echo sequences before and after gadolinium administration. Regions of interest were drawn within the L3 vertebral body from a parasagittal slice from each sequence. Signal intensity (SI) values were ascertained and the percentage increase in SI was calculated. For each patient, changes in receiver gain for pre- and post-gadolinium images were corrected by an image scaling factor. In all cases, a measurable increase in SI was found (mean 15.3%, range 4.4-55.7) due to bone vascularity. The results give no indication of the quantity or timing of blood supply but provide a basis for further work.

Dynamic contrast-enhanced MR imaging of the portal venous system: comparison with x-ray angiography.

PURPOSE: To compare dynamic contrast material--enhanced multisection magnetic resonance (MR) imaging with x-ray angiography in the evaluation of the portal venous system. MATERIALS AND METHODS: Eighteen patients underwent preoperative x-ray angiography and dynamic contrast-enhanced MR imaging. MR imaging was performed at 1.0 T with a multisection breath-hold fast low-angle shot (FLASH) technique in the coronal-oblique plane, before and after injection of a bolus of gadopentetate dimeglumine. The portal vein, its right and left intrahepatic branches, the splenic veins, and the superior mesenteric veins were examined. The presence of varices was also assessed. RESULTS: Of the 84 vessels evaluated with both techniques, appearances were similar in 76 (90%). Both examinations showed the main portal vein to be patent in nine patients, occluded in five, and patent but abnormal in two. Findings in the main portal vein were discordant in two patients. In one patient, surgical follow-up helped confirm the findings at MR imaging. CONCLUSION: MR imaging can replace x-ray angiography in the preoperative evaluation of portal vein patency in most patients.

A comparison of fast and conventional T2 weighted spin-echo sequences in the detection of focal liver lesions at 1.0T.

Conventional and fast T2-weighted spin-echo scans obtained at 1.0T were compared in 29 patients undergoing magnetic resonance imaging of the liver, 25 of whom had focal liver lesions. Conventional spin-echo (CSE) detected 49 of 50 lesions (98%), fast spin-echo (FSE) 45 of 50 lesions (90%). Qualitative assessment of lesion conspicuity, artefact level, and overall image quality by two radiologists showed conventional spin-echo was preferred to fast spin-echo. Lesion conspicuity was graded moderate or good in 84% of lesions on CSE compared to 73% on FSE. Artefact level was higher on FSE in 34%, equal in 61% and higher on CSE in 5%. Overall, CSE was preferred to FSE in 76% of cases. Mean lesion to liver contrast to noise ratio was significantly higher on conventional spin-echo than fast spin-echo: CSE mean 5.9, FSE mean 4.9 P < 0.05. This difference in contrast to noise ratio remained for malignant lesions, but no significant difference was present for cysts and haemangiomas. We advise careful assessment of new sequences before conventional T2-weighted spin-echo is replaced by fast T2-weighted spin-echo in the detection of focal liver lesions.