MRI of the axial skeletal manifestations of ankylosing spondylitis.

Magnetic resonance imaging (MRI) is a valuable tool in the imaging and assessment of patients with ankylosing spondylitis. MRI can demonstrate the acute and chronic changes of sacroiliitis, osteitis, discovertebral lesions, disc calcifications and ossification and arthopathic lesions, which characterize the disease, as well as the complications, which include fracture and the rare cauda equina syndrome. This article reviews the range of MRI findings commonly seen within the axial skeleton in patients with this condition.

Measurement of left ventricular volume after anterior myocardial infarction: comparison of magnetic resonance imaging, echocardiography, and radionuclide ventriculography.

We have compared echocardiography (echo) and radionuclide ventriculography (RNV) with magnetic resonance imaging (MRI) for the measurement of left ventricular (LV) volume and ejection fraction. Seventy asymptomatic patients were studied up to 12 days after first Q wave anterior myocardial infarction and again after 6 months. Each patient had LV volume measured by all three techniques within 24 hours of each other on each occasion. LV end-systolic and end-diastolic volume index (LVESVI and LVEDVI) and LV ejection fraction (LVEF) were measured using the modified Simpson formula (echo), a counts-based method (RNV), and a multislice area summation method (MRI). Radionuclide volumes were measured both with and without correction for attenuation of isotope. Echocardiography overestimated LV volume compared with MRI. Mean (SD) differences (echo-MRI) were: LVEDVI + 10.6 ml/m2 (16.8), LVESVI + 13.7 ml/m2 (12.9), LVEF -8.5% (11.2). RNV underestimated both volume and ejection fraction compared with MRI. Mean differences (RNV-MRI) were: LVEDVI -25.4 ml/m2 (23.8), LVESVI -5.0 ml/m2 (18.6), LVEF -13.8% (10.4). Variability in the difference between echo and MRI and between RNV and MRI was very similar for LVEF (coefficient of variation 23.9% echo, 22.2% RNV) but there was greater variability in the radionuclide than the echo measurements of absolute volume. Variability of the radionuclide measurements was reduced by not correcting for attenuation, and this finding may improve the radionuclide technique for serial measurements of percentage change in volume. Long-term inter-study reproducibility of MRI for LVEF (coefficient of reproducibility) was 10.9%, for echo it was 10.6%, and for RNV it was 14.6%. We conclude that measurements of LV volume depend on the method used and are not interchangeable. Echocardiography agrees more closely with MRI than RNV for the measurement of absolute volume, but the two techniques are similar for the measurement of LVEF.

Effect of systemic sclerosis on left ventricular long-axis motion and left ventricular mass assessed by magnetic resonance.

The aim of this study was to assess the effect of scleroderma on left ventricular mass and subendocardial function using cardiovascular magnetic resonance (CMR) to determine parameters reflecting early dysfunction from fibrosis. Fifteen patients with a history of scleroderma had left ventricular mass measured with standard techniques and regional subendocardial contractile function assessed using myocardial velocity mapping in the basal short-axis plane with long-axis sensitized velocity mapping. Peak myocardial velocities in systole and diastole were measured to reflect systolic and diastolic function. The variance in the regional myocardial velocity, was determined as a parameter of function heterogeneity around the ventricle. The results were compared with 19 healthy volunteers without a history of cardiovascular disease. In 10 patients, pulmonary transfer factor was measured using a single-breath helium dilution technique. The duration of scleroderma correlated with left ventricular mass (r = 0.7, p < 0.05), the coefficient of variation of velocity (r = 0.63, p < 0.05), and inversely with the mean left ventricular diastolic long-axis velocity (r = -0.63, p < 0.05). There was also a correlation between left ventricular diastolic long-axis velocity and the pulmonary transfer factor (r = 0. 7, p < 0.05). Trends suggested differences between control subjects and scleroderma patients for mean systolic (64 vs. 49 mm/sec, p = 0.09) and diastolic (90 vs. 72 mm/sec, p = 0.07) velocities, as well as velocity variance (26 vs. 33, p = 0.09). In conclusion, there is a relationship between duration of scleroderma and both left ventricular mass and diastolic function, which may result from increased myocardial fibrosis. Trends suggest absolute differences in functional values with control subjects that reflect impaired diastolic and systolic function, with greater regional heterogeneity that is consistent with nonuniform collagen deposition, but a larger sample size is required to confirm this. CMR should be explored further as a technique for monitoring myocardial involvement in scleroderma noninvasively.

The effect of cholesterol reduction with fluvastatin on aortic compliance, coronary calcification and carotid intimal-medial thickness: a pilot study.

BACKGROUND: Regression of atheroma with reduction of cholesterol levels is recognized to occur, but less is known about reversal of sclerosis. Non-invasive indices of sclerosis have largely been based on carotid ultrasound measurements. OBJECTIVE: To measure aortic compliance, coronary calcification and carotid intimal-medial thickness during reduction of cholesterol level in patients with and without coronary artery disease. METHODS: We studied 64 hypercholesterolaemic patients, 24 with and 40 without coronary artery disease. All were administered fluvastatin for 1 year. Aortic compliance was assessed using magnetic resonance and coronary calcification score was determined by electron beam computed tomography. Carotid intimal-medial thickness in 34 patients was measured by carotid ultrasound means. RESULTS: There was a rise in high-density lipoprotein cholesterol level and falls in total cholesterol level, low-density lipoprotein cholesterol level, low: high-density lipoprotein ratio, triglyceride level and very-low-density lipoprotein cholesterol level. Coronary artery disease patients had a higher coronary calcification score (442 +/- 551) than did other patients (269 +/- 724, P = 0.0002). For both groups there was a small rise in coronary calcification score during the study. Mean aortic compliance rose and blood pressure and carotid intimal-medial thickness fell. Analysis revealed significant correlations between change in mean aortic compliance and changes in high-density lipoprotein level (r = 0.3, P = 0.036), very-low-density lipoprotein level (r = -0.31, P = 0.038) and low: high-density lipoprotein ratio (r = -0.35, P = 0.014). There was no significant difference in these changes between the two patient groups. CONCLUSION: An improvement in aortic compliance over 1 year indicates that increase in high-density lipoprotein level, decrease in very-low-density lipoprotein level and improvement in low: high-density lipoprotein ratio caused by administration of fluvastatin beneficially influenced vascular pathophysiology in hypercholesterolaemic patients with and without coronary artery disease. In those patients studied with carotid ultrasound means, carotid intimal-medial thickness decreased from 1.09 to 0.87 mm (P = 0.004), corroborating these results.

Automatic tracking of the aorta in cardiovascular MR images using deformable models.

We present a new algorithm for the robust and accurate tracking of the aorta in cardiovascular magnetic resonance (MR) images. First, a rough estimate of the location and diameter of the aorta is obtained by applying a multiscale medial-response function using the available a priori knowledge. Then, this estimate is refined using an energy-minimizing deformable model which we define in a Markov-random-field (MRF) framework. In this context, we propose a global minimization technique based on stochastic relaxation, Simulated annealing (SA), which is shown to be superior to other minimization techniques, for minimizing the energy of the deformable model. We have evaluated the performance and robustness of the algorithm on clinical compliance studies in cardiovascular MR images. The segmentation and tracking has been successfully tested in spin-echo MR images of the aorta. The results show the ability of the algorithm to produce not only accurate, but also very reliable results in clinical routine applications.

Gated technetium-99m-tetrofosmin SPECT and cine MRI to assess left ventricular contraction.

UNLABELLED: This study investigates the value of ECG-gated 99mTc-tetrofosmin SPECT in the assessment of resting left ventricular (LV) function by comparison with cine MRI. METHODS: Twenty-eight patients were recruited prospectively from those referred for routine myocardial perfusion scintigraphy. Eight had three-vessel coronary artery disease, two had two-vessel disease, five had single-vessel disease and thirteen had not previously undergone coronary angiography. Twelve patients had previous myocardial infarction. After i.v. injection at rest of 750 MBq 99mTc-tetrofosmin, ECG-gated tomograms (16 frames per cardiac cycle) were acquired after 30 min. A nine-segment model of the LV was used and images were interpreted by two observers independently. Wall motion was assessed using a six-point scale (including unclassified where no judgment was possible), and systolic wall thickening was assessed from count changes through the cycle using a five-point scale. Tracer uptake was scored using a four-point scale. Diastolic wall thickness was assessed using a four-point scale. Cine magnetic resonance images were acquired in the same planes and analyzed in an identical fashion. RESULTS: There was good overall agreement between the techniques for wall motion, thickness and thickening (kappa = 0.55-0.66), although 15 of the 252 (6%) segments were unclassified on radionuclide imaging. While there was absolute agreement in the assessment of all parameters in 10 patients with normal wall motion by MRI, agreement was less good in the 8 patients with three-vessel disease and poor left ventricular function (mean LVEF = 26%, mean LVEDV = 241 ml) (kappa = 0.37-0.48). Where tracer uptake was normal, there was good agreement between imaging, techniques (kappa = 0.64-0.75), but where uptake was absent or nearly absent, agreement was poor (kappa = 0-0.61), and 15 of 22 segments were unclassified on SPECT. CONCLUSION: Gated 99mTc-tetrofosmin imaging provides an accurate assessment of myocardial wall motion, thickening and thickness in normal left ventricles but is less valuable in poorly functioning ventricles. Six percent of segments could not be assessed because of inadequate tracer uptake.

Echocardiography overestimates left ventricular mass: a comparative study with magnetic resonance imaging in patients with hypertension.

OBJECTIVE: To compare measurement of left ventricular mass (LVM) by M-mode echocardiography and magnetic resonance imaging (MRI) in hypertensive subjects. DESIGN: A prospective study. SUBJECTS: Twenty-four untreated hypertensive patients [19 men and five women, aged 51 +/- 2 (mean +/- SEM) years, supine blood pressure 159/101 +/- 3/1 mmHg]. SETTING: The Blood Pressure Unit, St Georges Hospital Medical School and Magnetic Resonance Unit, Royal Brompton National Heart and Lung Hospital, London. MAIN OUTCOME MEASURES: LVM estimated both by M-mode echocardiography and by MRI. RESULTS: Using three standard M-mode formulae, widely different values of LVM were obtained with echocardiography [American Society of Echocardiography (ASE) 319 +/- 21 g, Penn 273 +/- 19 g. Teichholz 191 +/- 11 g]. By MRI, the LVM was 232 +/- 11 g. The differences between MRI and echocardiography could not be explained in terms of the timing of measurements in the cardiac cycle. When single-slice MRI measurements at the appropriate level were applied to the ASE and Penn formulae, the LVM was again overestimated. CONCLUSION: Our study has shown major differences in LVM estimated using methods based on one-dimensional (echocardiography) compared with three-dimensional (MRI) data. These differences seem to be largely the result of the geometrical assumptions on which M-mode measurements are based. Our findings have important clinical implications for the assessment of the severity and response to treatment of left ventricular hypertrophy in hypertensive patients.

Rapid assessment of left ventricular volume by short axis cine MRI.

MRI is an established and accurate method of measuring left and right ventricular volumes by summing chamber areas in multiple contiguous slices. Acquisition time may be up to 45 min. We have estimated volumes with gradient echo imaging to test the accuracy of a more rapid method (total acquisition time 15 min) using a recognized echocardiographic algorithm. The results were compared with the spin echo method. We studied 20 patients (mean age 52 years, 15 male) within 6 months of anterior myocardial infarction and 20 normal subjects (mean age 40 years, 19 males). For the rapid method, cine acquisitions were made in the horizontal long axis plane and in two short axis planes which divided the long axis into three equal parts. Volume was calculated assuming the ventricle to be composed of a cylinder, a truncated cone and a cone. There was good agreement between the two methods at end diastole with a mean difference (+/- standard error, +/- 95% confidence interval for limits of agreement) of -3 ml (+/- 8.3, +/- 37%) for normal subjects and 1.5 ml (+/- 4.2, +/- 25%) for patients. Agreement was less good at end systole with mean difference of 12.1 (+/- 3.5, +/- 41%) for normal subjects and 25.7 (+/- 3.7, +/- 47%) for patients. The rapid method, therefore, significantly underestimated end systolic volume compared with the previous method. Rapid measurements of end diastolic volume are more accurate than those of end systolic volume and hence ejection fraction. Provided the potential error is recognized, the rapid technique can be used in routine clinical practice in both normal and abnormal ventricles.

Measurement of regional aortic compliance by MR imaging: a study of reproducibility.

The reproducibility of MR imaging for the measurement of aortic compliance was studied in 47 healthy volunteers. Long and short term reproducibility and intraobserver variability were tested. The method was modified to improve image quality and short term reproducibility and intraobserver variability retested. For comparison, spin echo imaging was compared with cine gradient echo imaging. Initial long term reproducibility showed a mean difference (+/-SE) of 3% (+/- 7%) with 95% confidence interval (CI) for limits of agreement of +/- 69%. Short term reproducibility (7% +/- 6%, 95% CI +/- 46%) and intraobserver variability (1% +/- 2%, 95% CI +/- 31%) were better. After modification of the technique and optimization of image quality, both short term reproducibility and intraobserver variability improved (0% +/- 3%, 95% CI +/- 17% and 5% +/- 2%, 95% CI +/- 16% respectively). Aortic compliance can be measured using spin echo MR imaging with good reproducibility provided care is taken to obtain good quality images with high spatial resolution.

Adenosine combined with dynamic exercise for myocardial perfusion imaging.

OBJECTIVES: This study investigated whether combining exercise with adenosine would reduce the adverse effects of adenosine vasodilation. BACKGROUND: Adenosine vasodilation is effective for perfusion imaging but causes frequent unpleasant noncardiac adverse effects, high noncardiac tracer uptake and occasional arrhythmias. METHODS: Of 500 consecutive patients referred for thallium-201 myocardial perfusion imaging, 407 were randomized to three study groups: 6 min of adenosine infusion alone; 6 min of adenosine with submaximal exercise; or symptom-limited exercise with continuous adenosine. Minimal detectable differences are presented; a significance level of 0.05 with a power of 80% is assumed. RESULTS: There was no difference among the three groups in sensitivity and specificity (overall 96% and 78%, minimal detectable differences 5.5% and 11%, respectively) for detection of coronary artery disease or stenosis in individual coronary arteries. There was a trend toward improved sensitivity in the combined exercise groups compared with that in the adenosine-only group (98% vs. 93%, p = 0.07, minimal detectable difference 6%). Noncardiac side effects were reduced by 43% in the exercise groups (p < 0.0001), and major arrhythmias were reduced by 90% (p < 0.0001). There was no effect on minor arrhythmias (25% vs. 22%, p = 0.6, minimal detectable difference 12%). The heart/background ratios were higher in the exercise groups (all p < 0.02). Each ratio was correlated with the exercise level achieved (all p < 0.001). The reversibility score increased with exercise (p = 0.04), as did the number of patients and segments with reversible defects (both p = 0.03). CONCLUSIONS: Combining exercise with adenosine infusion reduced the noncardiac side effects of vasodilation and major arrhythmias while improving redistribution and heart/background ratios. These findings may be clinically important. Although maximal exercise with adenosine infusion produced optimal results, the improvement over the submaximal exercise protocol was minor, and this has the advantage of being simple and achievable within the normal 6-min duration of the adenosine infusion.

Technical note: rapid measurement of left ventricular mass by spin echo magnetic resonance imaging.

Magnetic resonance (MR) imaging provides an accurate measurement of left ventricular mass but imaging time can be up to 45 min. We tested a more rapid multislice spin echo technique on 16 volunteers without evidence of heart disease. Multislice short axis spin echo images were acquired in up to three sets of five, clustered around end systole. Total imaging time was 15 min. Myocardial areas were summed and specific gravity was assumed. Comparison was made with multiple single acquisitions timed to end systole. There was good agreement between the two measurements of left ventricular mass. Mean (+/- standard deviation (sd), range) values were 212 g (+/- 41.71, 152 to 311) by the multislice method and 213 g (+/- 44.26, 155 to 317) by the single slice method. The mean difference (+/- sd of difference) between measurements was -1.72 +/- 14.89 g (95% confidence interval for limits of agreement was +/- 14%). We have therefore established a more rapid and accurate method of measuring left ventricular mass.