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.

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.

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.

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.

Cine MRI using steady state free precession in the radial long axis orientation is a fast accurate method for obtaining volumetric data of the left ventricle.

In this study we assessed the use of a steady state free precession (SSFP) cine sequence in a series of radially orientated long axis slices for the measurement of left ventricular volumes and mass. We validated the radial long axis approach in phantoms and ex vivo porcine hearts and applied it to normal volunteers and patients using the SSFP and turbo gradient-echo (TGE) sequences. High quality images were obtained for analysis, and the measured volumes with radial long axis SSFP sequence correlated well with short axis TGE and SSFP volumes (r > 0.98). The best interobserver agreement for left ventricular volumes was obtained using SSFP in the long axis radial orientation (variability < 2.3%). We conclude that this combination of sequence and scan orientation has intrinsic advantages for image analysis due to the improved contrast and the avoidance of errors associated with the basal slice in the short axis orientation.

Steady-state free precession magnetic resonance imaging of the heart: comparison with segmented k-space gradient-echo imaging.

Steady-state free precession imaging is a promising technique for cardiac magnetic resonance imaging (MRI), as it provides improved blood/myocardial contrast in shorter acquisition times compared with conventional gradient-echo acquisition. The better contrast could improve observer agreement and automatic detection of cardiac contours for volumetric assessment of the ventricles, but measurements might differ from those obtained using conventional methods. We compared volumetric measurements, observer variabilities, and automatic contour detection between a steady-state free precession imaging sequence (BFFE = balanced fast field echo) and segmented k-space gradient-echo acquisition (TFE = turbo field echo) in 41 subjects. With BFFE, significantly higher end-diastolic and end-systolic volumes and lower wall thickness, ventricular mass, ejection fraction, and wall motion were observed (P < 0.0001), while interobserver variabilities were lower and automatic contour detection of endocardial contours was more successful. We conclude that the improved image quality of BFFE reduces the observer-dependence of volumetric measurements of the left ventricle (LV) but results in significantly different values in comparison to TFE measurements.

Measurements of left ventricular dimensions using real-time acquisition in cardiac magnetic resonance imaging: comparison with conventional gradient echo imaging.

This study investigates the use of real-time acquisition in cardiac magnetic resonance imaging (MRI) for measurements of left ventricular dimensions in comparison with conventional gradient echo acquisition. Thirty-one subjects with a variety of left ventricular morphologies to represent a typical clinical population were studied. Short-axis data sets of the left ventricle (LV) were acquired using a conventional turbo-gradient echo and an ultrafast hybrid gradient echo/echo planar sequence with acquisition in real-time. End-diastolic volume (EDV), end-systolic volume (ESV), ejection fraction (EF) and left ventricular mass (LV mass) were measured. The agreement between the two acquisitions and interobserver, intraobserver and interstudy variabilities were determined. The bias between the two methods was 5.86 ml for EDV, 0.23 ml for ESV and 0.94% for EF. LV mass measurements were significantly lower with the real-time method (mean bias 14.38 g). This is likely to be the result of lower spatial resolution and chemical shift artefacts with the real-time method. Interobserver, intraobserver and interstudy variabilities were low for all parameters. In conclusion, real time acquisition in MRI can provide accurate and reproducible measurements of LV dimensions in subjects with normal as well as abnormal LV morphologies, but LV mass measurements were lower than with conventional gradient echo imaging.

Qualitative and quantitative analysis of regional left ventricular wall dynamics using real-time magnetic resonance imaging: comparison with conventional breath-hold gradient echo acquisition in volunteers and patients.

A real-time magnetic resonance imaging (MRI) acquisition sequence was evaluated for the assessment of left ventricular wall motion (WM) and wall thickening (WT). Ten normal volunteers and 21 patients were studied. Short-axis cine images of the left ventricle (LV) were acquired with a fast gradient echo and an ultrafast segmented echo-planar imaging (EPI) sequence. Qualitative and quantitative analysis of WM and WT was performed on a segmental basis. Qualitative scores agreed between the two methods in 691 of 724 segments (95.4%) with good reproducibility. Quantitative measurements of WM and WT were significantly lower (P < 0.001) with the real-time method (WM: mean bias, 0.49 mm; WT: mean bias, 0.61 mm). The largest differences were observed in the anterior and lateral segments and in patients with dilated ventricles. The lower resolution of the real-time sequence and artifacts was probably responsible for these differences. In conclusion, real-time cardiac MRI can be used for qualitative assessment of wall dynamics but is presently insufficient for quantitative analysis.

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.

Quantitative comparison of intrabrain diffusion in adults and preterm and term neonates and infants.

OBJECTIVE: Quantitative measurements of mean water diffusivity (D(av)) were made in human neonates, infants, and adults to assess changes in brain tissue that occur with maturation. SUBJECTS AND METHODS: Values of D(av) were obtained by calculating the average of the diffusion measurements made with diffusion-sensitizing gradients placed along three orthogonal directions. The mean diffusivity, a rotationally invariant determination of apparent diffusion coefficient, was measured in five healthy prematurely born neonates and infants, in 10 healthy term neonates and infants, and in five adults. RESULTS: Values of D(av) were found to decrease with maturation in most parts of the brain. In prematurely born neonates and infants with a postmenstrual age (postgestastional age + postnatal age) under 36 weeks, the average value of D(av) in frontal white matter was 1.90 x 10(-3) mm2 sec(-1). The corresponding value was measured as 1.62 x 10(-3) mm2 sec(-1) in neonates and infants born at term with a postnatal age of no more than 43 days and 0.79 x 10(-3) mm2 sec(-1) in the adult brain. CONCLUSION: Values of D(av) are known to decrease in neonates and young infants in the period immediately after ischemic insult. This decrease and the associated increase in signal intensity seen on diffusion-weighted imaging have been used to monitor ischemic brain injury in neonates and infants. Therefore, the decrease in D(av) that occurs with maturation, which we report in this study, must be considered if quantitative diffusion measurements are used to assess ischemic neonatal brain injury.

Intra-articular primatised anti-CD4: efficacy in resistant rheumatoid knees. A study of combined arthroscopy, magnetic resonance imaging, and histology.

OBJECTIVES: CD4+ T cells sustain the chronic synovial inflammatory response in rheumatoid arthritis (RA). SB-210396/CE 9.1 is an anti-CD4 monoclonal antibody that has documented efficacy in RA when given intravenously. This study aimed to establish the safety and efficacy of the intra-articular administration of SB-210396/CE 9.1 compared with placebo, examining its mode of action using a combined imaging approach of arthroscopy, magnetic resonance imaging (MRI), and histology. METHODS: Thirteen RA patients with active, resistant knee synovitis, were randomised to intra-articular injection of placebo (n=3), 0.4 mg (n=3) or 40 mg (n=7) of anti-CD4 after sequential dynamic gadolinium enhanced MRI, followed by same day arthroscopy and synovial membrane biopsy. Imaging and arthroscopic synovial membrane sampling were repeated at six weeks. This study used a unique region of interest (ROI) analysis mapping the MRI area analysed to the specific biopsy site identified arthroscopically, thus providing data for all three modalities at the same synovial membrane site. RESULTS: 12 patients completed the study (one placebo treated patient refused further MRI). Arthroscopic improvement was observed in 0 of 2 placebo patients but in 10 of 10 patients receiving active drug (>20% in 6 of 10). Improvement in MRI was consistently observed in all patients of the 40 mg group but not in the other two groups. A reduction in SM CD4+ score was noted in the 40 mg group and in the 0.4 mg group. Strong correlations both before and after treatment, were identified between the three imaging modalities. Intra-articular delivery of SB-210396/CE 9.1 was well tolerated. CONCLUSIONS: SB-210396/CE 9.1 is safe when administered by intra-articular injection. A trend toward efficacy was found by coordinated MRI, arthroscopic, and histological imaging, not seen in the placebo group. The value of ROI analysis was demonstrated.

Stepping-table gadolinium-enhanced digital subtraction MR angiography of the aorta and lower extremity arteries: preliminary experience.

PURPOSE: To compare stepping-table digital subtraction gadolinium-enhanced magnetic resonance (MR) angiography of the distal aorta and lower extremity arteries with conventional catheter digital subtraction x-ray angiography in patients with arterio-occlusive disease. MATERIALS AND METHODS: Twenty patients underwent both conventional catheter angiography and fast three-dimensional gadolinium-enhanced MR angiography of the aorta and outflow vessels at 1.5 T; the images were acquired in three consecutive imaging locations during a single infusion of a gadolinium chelate. RESULTS: Compared with catheter angiography, according to the findings of two blinded independent reviewers, MR angiography had sensitivities of 81% and 89% and specificities of 91% and 95%, respectively, for demonstration of insignificant (< or = 50%) stenosis versus significant (51%-100%) stenosis. For demonstration of occlusion, the sensitivity and specificity were 94% and 97%, respectively, by consensus. There was good interobserver correlation between the two readers overall (kappa = 0.65 for reporting the degree of narrowing in all lesions; 0.86, for reporting of insignificant versus significant stenoses; and 0.928, for reporting of occluded versus patient segments). CONCLUSION: Stepping-table digital subtraction contrast material-enhanced MR angiography has high accuracy compared with catheter angiography in patients with arterio-occlusive disease of the aorta and outflow vessels. These preliminary study results suggest that this technique may ultimately provide a safe, noninvasive, and cost-effective alternative to catheter angiography.

Frequency-domain simulation of MR tagging.

Simulation of MR images is a useful tool for offline sequence development and as an aid to understanding image formation. One particular application of simulation is MR tagging, which is used for tracking myocardial motion. Simple spatial-domain methods cannot adequately represent effects common in these images, such as motion artifact and signal wrap. An existing frequency-domain model is shown to be inappropriate for tagged images, and an extension based on the Bloch equations and Fourier shift theorem is described to correct this. Software incorporating the new model is used to generate ideal tag intensity profiles and to accurately simulate tagged images. The shifted k-space patterns associated with tagged images, and their dependence on the order of the binomial tagging sequence, are explained. An application of the Fourier shift theorem is suggested that allows more rapid simulation of static tagged images.

Simulation of two-dimensional tagged MRI.

MR tagging is a recent imaging development that, in cardiac applications, makes possible the tracking of points in the myocardium during the cardiac cycle. Researchers have developed semiautomated, computer-based methods for analyzing tagged images, but the images are complex and present a challenge to automated tracking systems. Simulation can provide an inexhaustible supply of images for testing and validation of tag tracking software and preview the effect of parameter changes in acquisition. SIMTAG is an interactive computer program that simulates two-dimensional tagged-MR experiments. The mathematic model used in the simulation and algorithms for simulating image noise and object deformation are described. Examples of the use of simulated images in SPAMM parameter selection, a comparison of tag contrast in signal-averaged SPAMM and CSPAMM, and simulated images as test sets for tag-tracking software are presented.

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.

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.

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.