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R H Mohiaddin,
E D Burman,
S K Prasad,
A Varghese,
R S Tan,
S A Collins,
R L Hughes,
P D Gatehouse,
P Jhooti, D B Longmore,
G Z Yang,
D N Firmin,
D J Pennell
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ABSTRACT: Aortic atherosclerosis and coronary artery disease (CAD) are closely linked. Early detection of aortic atherosclerosis with the adoption of appropriate preventive measures may therefore help to reduce mortality and morbidity related to CAD. Arterial remodeling, by which the wall adapts to physiological or pathological insults by a change in vessel size, is being increasingly recognized as an important aspect of atherosclerosis. In this prospective longitudinal study we used cardiovascular magnetic resonance (CMR) to detect aortic plaque and to study aortic wall remodeling in asymptomatic subjects.
We recruited 175 healthy volunteers (49 years, 110 men) and documented their cardiovascular risk profile. Each subject underwent echocardiogram (ECG)-gated T1-weighted spin-echo imaging of the infrarenal abdominal aorta at baseline and after 2 years.
Of the 175 subjects who volunteered at baseline, CMR was successful in 174 (99%), with one (0.6%) failure due to claustrophobia. At 2 years, follow-up scanning was performed in 169 subjects (97%). Infrarenal aortic plaque was identified at baseline in nine (5.2%) subjects. This was reconfirmed in all nine (100%) cases at 2-year follow-up. No new cases of infrarenal plaque were identified at follow-up. The signal characteristics of the plaque on the subtracted images of the Dixon method indicate that all plaques were fibrous. In the nine subjects with infrarenal plaque, the total plaque burden increased as assessed by the total wall volume (561 to 677 mm3, p = 0.0063). The total vessel volume also increased (1737 to 1835 mm3, p = 0.031) but there was no change in the total luminal volume (1175 to 1157 mm3, p = 0.29).
Cardiovascular magnetic resonance detects subclinical aortic atherosclerosis, can follow plaque burden over time, and confirms the presence of Glagov remodeling with preservation of the lumen despite progression of plaque. Cardiovascular magnetic resonance is well suited for the longitudinal follow-up of the general population with atherosclerosis, may help in the understanding of the natural history of atherosclerosis, and in particular may help determine factors to retard disease progression at an early stage.
Journal of Cardiovascular Magnetic Resonance 02/2004; 6(2):517-25. · 3.72 Impact Factor
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ABSTRACT: Magnetic resonance cine imaging of left ventricular wall motion at rest or during stress may be used to assess myocardial function, infarction and viability, or reversible ischaemia. Whilst interpretation of the cines rests critically on image quality, there is little in the literature which systematically examines the optimal imaging parameters for such wall motion studies at rest or during stress. This study was designed to examine several imaging parameters for cine optimization using a conventional 0.5 T scanner. Gradient echo imaging was performed in two groups of volunteers with varying echo times and flip angles. The period between excitations was 80 ms (simulating a resting heart rate) in one group, and 40 ms (simulating tachycardia during stress) in the other group. Short axis imaging yielded the highest contrast between blood and myocardium for both repetition times (rest p = 0.02; stress p < 0.001) compared with the long axes, because of magnetic saturation of blood moving slowly in-plane. Contrast was higher at end-diastole than end-systole for the long axes (rest p < 0.0001; stress p < 0.0002), but not significantly different in the short axis. Increasing the echo time and flip angle resulted in increased signal but eventually caused motion artefact and magnetic saturation of blood. The optimal parameters were an echo time of 14 ms and a 45 degrees flip angle for resting heart rates, with the flip angle falling to between 35 degrees and 45 degrees for tachycardia. The choice of imaging parameters is therefore a compromise between improved signal and unwanted artefacts, although the latter are less evident in the short axis plane, which yields the best contrast results because of high blood inflow effects.
British Journal of Radiology 10/1998; 71(850):1033-9. · 1.31 Impact Factor
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ABSTRACT: Noise filtering of images is essentially a smoothing process and
it is an issue that has been addressed for many years. The most commonly
used low-pass filtering methods blur important image structures such as
edges and lines thus reducing the image contrast and damaging image
fidelity. The paper presents a structure adaptive anisotropic filtering
method with its application to processing multidimensional magnetic
resonance images
Image Processing and its Applications, 1995., Fifth International Conference on; 08/1995
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ABSTRACT: Magnetic resonance imaging (MRI) is a versatile technique for examination of the cardiovascular system but only recently has assessment of myocardial ischaemia in coronary artery disease (CAD) become possible, for example by demonstrating abnormalities of regional ventricular contraction during stress. Global ventricular function during stress was assessed by MRI of aortic flow, which has not been previously attempted.
Variables measured by MRI reflecting the effect of ischaemia on global ventricular function during dobutamine stress were correlated with thallium-201 myocardial perfusion tomography.
10 normal controls and 25 patients with CAD.
Tertiary cardiac referral centre.
Novel MRI sequences and analysis systems were used to measure the following variables during staged dobutamine infusion to 20 micrograms/kg/min: stroke volume, cardiac output, cardiac power output, peak flow, peak flow acceleration, aortic back flow, and flow wave velocity. Heart rate, blood pressure, double product, and maximum tolerated dobutamine dose were also measured. Multiple regression analysis was used to compare changes during stress with 201TI tomography.
All parameters except for stroke volume and diastolic blood pressure increased in the controls. In the patients with CAD a significant relation was shown between the extent of reversible ischaemia and the change in peak flow acceleration (P < 0.00001), peak flow (P = 0.002), cardiac power output (P = 0.036), maximum dobutamine dose (P = 0.039), and systolic blood pressure (P = 0.04). Peak flow acceleration accounted for 58.4% of the variation in reversible ischaemia, and after allowing for this, only cardiac power output remained independently predictive adding a further 4.2% to the model (adjusted r2 = 0.626). A decrease in peak flow acceleration with an increase in dobutamine infusion indicated moderate or severe ischaemia (chi 2 = 10.2, P = 0.017).
MRI may be used to assess variables of aortic flow during stress, which includes acceleration with high temporal resolution. Peak flow acceleration was the most sensitive indicator of the effect of ischaemia on global ventricular function.
Heart 08/1995; 74(2):163-70.
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ABSTRACT: Functional evaluation of the cardiovascular system using rapid imaging (spiral echo planar), chemical shift, and velocity mapping is capable of making the diagnosis in congenital and acquired cardiovascular disease which, between them, cause the largest number of deaths of any disease in the western world and massive morbidity and suffering. Furthermore, for the first time in the history of medicine, there is the opportunity to apply preventive measures to eardicate the epidemic of preventable arterial disease. There needs to be a change of emphasis and a switching of resources to apply to the most common diseases rather than to those which are most easily studied. There also needs to be proper training in cardiovascular MR, not so much for imagers as for cardiologists and experts in vascular disease.
MAGMA Magnetic Resonance Materials in Physics Biology and Medicine 09/1994; 2(3):211-217. · 1.88 Impact Factor
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ABSTRACT: The work describes the development of a novel sequence that uses rapid spiral k-space sampling, combined with phase velocity mapping, for real time flow velocity imaging. The performance of the technique is assessed on phantoms for both through-plane and in-plane flows. The flow measurements compared well with those measured using a bucket and stopwatch. One advantage of the technique is that flow related signal loss is minimal due to the early acquisition of the center of k-space data. Flow artifacts were observed for in-plane flow and these were understood with the aid of computer simulations. In vivo studies involved cine velocity mapping in normal volunteers; aortic blood flow waveforms acquired by spiral scanning in two cardiac cycles compared well with data from a conventional gradient-echo sequence. Potential applications of the method are demonstrated by studying the response of aortic flow to physical exercise and the real time monitoring of aortic flow during a valsalver maneuver.
Magnetic Resonance in Medicine 06/1994; 31(5):504-12. · 2.96 Impact Factor
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ABSTRACT: 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.
British Journal of Radiology 02/1994; 67(793):86-90. · 1.31 Impact Factor
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ABSTRACT: We used magnetic resonance imaging with cine velocity mapping to study the anatomy of pulmonary bifurcation and to measure volume blood flow, pulsatility of flow and arterial wall distensibility in the central pulmonary arteries of nine healthy volunteers. Multislice, multiplane spin echo images were acquired to display pulmonary bifurcation anatomy. Diameters of the main pulmonary artery (MPA) in systole were 2.56 +/- 0.35 cm and in diastole 2.20 +/- 0.33 cm. Those of the right pulmonary artery (RPA) were 1.57 +/- 0.29 cm and 1.39 +/- 0.23 respectively, and of the left pulmonary artery (LPA) 1.79 +/- 0.26 cm and 1.55 +/- 0.10 cm respectively. A gradient echo sequence with phase shift velocity mapping was then used to measure flow in MPA, RPA and LPA 2 cm on either side of the pulmonary bifurcation. Time averaged flow, calculated from mean velocity and the cross-sectional area of the vessels was 4.99 +/- 1.10 l.min-1 in MPA, 2.23 +/- 0.58 l.min-1 in RPA and 2.31 +/- 0.63 l.min-1 in LPA. The pulsatility index of flow derived from peak forward flow, peak backward flow and time averaged flow were as follows: MPA 4.4 +/- 0.8, RPA 5.1 +/- 0.6 and LPA 4.6 +/- 1.5. Distensibility, calculated from the change in cross-sectional area between diastole and systole and expressed as percentage were as follows: MPA 25.6 +/- 10.7, RPA 21.4 +/- 10.7 and LPA 24.5 +/- 7.8. MRI with velocity mapping accurately characterized anatomy, flow, distensibility and pulsatility of the central pulmonary arteries.
European Heart Journal 12/1993; 14(11):1524-30. · 10.48 Impact Factor
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ABSTRACT: Helical and retrograde secondary flows have been recorded in the aorta, but their origins and movements in relation to the arch have not been clarified. We set out to do this using magnetic resonance velocity mapping.
Three-directional phase contrast cine magnetic resonance velocity mapping was used to map multidirectional flow velocities in the aortas of 10 healthy volunteers. Computer processing was used to visualize flow vector patterns in selected planes. Right-handed helical flows predominated in the upper aortic arch in late systole, being clearly recognizable in 9 of the 10 subjects. Nonaxial components of velocity in this region reached 0.29 m/s (+/- 0.05 m/s) as axial velocities declined from a peak of 1.0 m/s (+/- 0.1 m/s). Helical flow patterns in the upper descending aorta varied between subjects, apparently depending on arch curvature. End-systolic retrograde flow originated from regions of blood with low momentum, usually along inner wall curvatures. Flow studies in a curved tubular phantom showed right-handed helical flow in the upper "arch" when the inflow section was positioned to simulate ascending aortic curvature, and retrograde flow occurred along the inner wall at end systole during pulsatile flow.
Helical and retrograde streams are consistent features of intra-aortic flow in healthy subjects that result, at least in part, from the curvature of the arch and the pulsatility of flow in it. They may have significance in relation to circulatory dynamics and the pathogenesis of atheroma in the arch.
Circulation 12/1993; 88(5 Pt 1):2235-47. · 14.74 Impact Factor
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ABSTRACT: Nuclear magnetic resonance (MRI) velocity mapping was used to characterize flow waveforms and to measure volume flow in the ascending and descending thoracic aorta in patients with aortic coarctation and in healthy volunteers. We present the method and discuss the relation between these measurements and aortic narrowing assessed by MRI. Finally, we compare coarctation jet velocity measured by MRI velocity mapping with that obtained from continuous wave Doppler echocardiography.
The development of a noninvasive imaging method for morphologic visualization of aortic coarctation and for measurement of its impact on blood flow is highly desirable in the preoperative and postoperative management of patients.
Magnetic resonance imaging phase-shift velocity mapping was used to measure ascending and descending aortic volume flow in 39 patients with aortic coarctation and in 12 healthy volunteers. Magnetic resonance imaging was also used for anatomic and peak jet velocity measurements. The latter were compared with those available from continuous wave Doppler study in 40% of the patients.
Whereas ascending aortic volume flow measurement did not show significant differences between the patient and healthy control groups, volume flow curves in the descending aorta did show significant differences between the two groups. Peak volume flow (mean +/- SD) was 10.6 +/- 5.3 liters/min in patients and 19.6 +/- 4.7 liters/min in control subjects (p < 0.001). Time-averaged flow was 2.5 +/- 0.9 liters/min in patients and 3.9 +/- 1.1 liters/min in control subjects (p < 0.05). The descending/ascending aorta flow ratio was 0.47 +/- 0.19 in patients and 0.64 +/- 0.08 in control subjects (p < 0.05). These variables correlate well with the degree of aortic narrowing. Peak coarctation jet velocity measured by MRI velocity mapping is comparable to that obtained from continuous wave Doppler study (r = 0.95).
We established normal ranges for volume flow in the descending aorta and demonstrated abnormalities in patients with aortic coarctation. These abnormalities are likely to be related to resistance to flow imposed by the coarctation and could represent an additional index for monitoring patients before and after intervention.
Journal of the American College of Cardiology 11/1993; 22(5):1515-21. · 14.16 Impact Factor
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ABSTRACT: Coronary artery imaging is an important investigation for the management of coronary artery disease. The only reliable technique presently available, x ray contrast angiography, is invasive and is associated with a small morbidity and mortality. Alternative non-invasive imaging would be useful, but the small calibre and tortuosity of the coronary vessels, and cardiac and respiratory motion create formidable imaging problems.
The development of rapid magnetic resonance imaging of the coronary arteries.
21 healthy controls and five patients with coronary artery disease established by x ray contrast angiography, of whom two had undergone bypass grafting.
Magnetic resonance imaging was performed with gradient echoes and a segmented k-space technique, such that a complete image was acquired in 16 cardiac cycles during a breathhold. The signal from fat was suppressed and images were acquired in late diastole to reduce artefact from cardiac motion. An imaging strategy was developed for the proximal arteries, including longitudinal imaging from oblique planes defined according to the origins and the continuation of the arteries in the atrioventricular grooves or interventricular sulcus.
Of the 26 subjects studied, 22 were imaged successfully. Identification of the artery was possible for the left main stem, left anterior descending, right coronary, and left circumflex arteries respectively in 95%, 91%, 95%, and 76%. The arterial diameter at the origin could be measured in 77%, 77%, 81%, and 63%. The mean (SD) arterial diameter in each case (4.8 (0.8), 3.7 (0.5), 3.9 (0.9), and 2.9 (0.6) mm) was not significantly different from reference values. The mean length of artery visualised was 10.4 (5.2), 46.7 (22.8), 53.7 (27.9), and 26.3 (17.5) mm. In 12 healthy men the total coronary area was 30.9 (9.2) mm2 and the ratio compared with body surface area was 16.4 (4.4) mm2m2 (both p = NS compared with reference values). In seven patients in whom x ray contrast coronary angiography was available, the proximal arterial diameter was 3.9 (1.1) mm measured by magnetic resonance and 3.7 (1.0) mm by x ray contrast angiography (p = NS). The mean difference between the measurements was 0.2 (0.5) mm, and the coefficient of variation was 13.7%. All five occluded coronary arteries were identified, as were all three vein grafts. In two patients insertion of the graft into the native arteries was identified.
Magnetic resonance coronary angiography is feasible. Good results were obtained by a breath-hold, fat suppression technique, gated to late diastole. Arterial occlusions and vein grafts were readily identified. Further studies are required to establish its value in the detection of coronary stenosis and to develop the measurement of coronary flow velocity which could be used to quantify the severity of the stenosis.
Heart 11/1993; 70(4):315-26.
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ABSTRACT: A method is described for acquiring 7-dimensional information
about flowing blood. The acquisition of the 7-dimensions, consisting of
3 spatial, 3 velocity and 1 time, enables a more complete study of blood
flow patterns than had previously been possible. In order to reduce the
scan time to acceptable levels, the method uses a 2-D selective r.f.
pulse to excite a column of tissue and a limited number of phase
encoding steps to spatially resolve across the short axes of the column.
Phase velocity mapping is used to quantify velocities in 3 perpendicular
directions. Recent hardware developments should enable rapid processing
of the large data sets acquired
Computers in Cardiology 1993, Proceedings.; 10/1993
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ABSTRACT: Addresses a distributed approach for medical image database
systems and its implementation. Compared with a centralized approach,
distributed strategy has the advantage of fault-tolerance, ease of
integration, lower network traffic and faster system response. Various
practical aspects of the system design with respect to data storage
hierarchy, image format, system communication and resource sharing are
discussed. An implementation example which incorporates cardiac MR, CT
and nuclear medicine imaging systems is presented. The system is based
on a Novell and TC/PIP local area network. It has also been further
integrated into a hospital information system which controls the patient
registration and resource allocation
Computers in Cardiology 1993, Proceedings.; 10/1993
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ABSTRACT: Using quantitative magnetic resonance (MR) flow imaging techniques
for performing in vivo flow, measurement has already established its
value in medical practice. Due to time limitations, however, compromises
have to be made in studies of 3-dimensional pulsatile flow. Velocity
distributions are usually acquired only in selected imaging planes.
Although recent development of rapid MR 3D cine flow imaging techniques
has greatly improved the comprehensiveness of flow data acquired, it is
achieved at the cost of some reduction of signal to noise ratio and
spatial resolution. The objective of this study is to use the technique
of convex projections to reconstruct 3D velocity fields from incomplete
or noisy data sets. The theory and numerical implementation of these
projectors are presented
Computers in Cardiology 1993, Proceedings.; 10/1993
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Circulation 08/1993; 88(1):264-81. · 14.74 Impact Factor
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ABSTRACT: Magnetic resonance (MR) phase-shift velocity mapping is an established method for measurement of nonturbulent intravascular flow. Shortening the echo time of the MR sequence to 3.6 msec allowed application of the technique to turbulent jet flow. The objective of this study was validation of MR jet velocity mapping in patients with cardiac valve stenosis.
We used a 0.5-T Picker MR machine to measure peak poststenotic jet velocity in 15 consecutive patients recruited with known valve disease (six mitral stenosis, three of these restudied after valvoplasty, and 11 aortic stenosis). On the same day as the MR study, these patients underwent independent Doppler echocardiographic measurement of peak jet velocity. The results of 10 further MR investigations of aortic stenosis are also reported and compared with Doppler studies performed within 6 months. Of the 29 MR studies, 28 (97%) produced interpretable velocity maps, the one failure being attributed to misplacement of the imaging slice in a case of severe aortic stenosis. Agreement between MR and Doppler measurements of peak jet velocity in the recruited group was as follows: n = 18; range, 1.4-6.1 m/sec; mean, 3 m/sec; mean of differences (MR-Doppler), 0.23 m/sec; standard deviation of differences, 0.49 m/sec.
In vivo MR peak jet velocity measurements agree well with those made by Doppler ultrasound. The technique, which is not subject to restricted windows of access and has potential for further refinements, could contribute to improved evaluation of stenoses, especially at locations where ultrasonic access is limited.
Circulation 05/1993; 87(4):1239-48. · 14.74 Impact Factor
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ABSTRACT: We have used magnetic resonance imaging with cine velocity mapping to measure flow wave velocity in the thoracic aorta of 20 healthy volunteers of different ages. We have also studied the relationship between propagation of flow wave velocity and regional aortic compliance. Aortic flow velocity increased linearly with age (r = 0.87), and there was a significant difference between the youngest decade [age 10-19, mean velocity 4.3 +/- 0.7 (SD) m/s] and the oldest decade studied (age 50-59, mean velocity 7.2 +/- 0.2 m/s). Flow wave velocity (m/s) was negatively correlated with ascending aortic compliance (microliter/mmHg) (r = -0.75). Magnetic resonance imaging is a noninvasive method for measurement of aortic flow wave velocity that is an important parameter in assessing arterial wall mechanics and blood flow dynamic.
Journal of Applied Physiology 02/1993; 74(1):492-7. · 3.75 Impact Factor
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ABSTRACT: Magnetic resonance phase-shift-induced velocity mapping is a powerful technique for measuring in vivo blood velocity and flow non-invasively. Using this method we examined dimensions, distensibility, blood flow and its regional distribution in the abdominal aorta in 10 normal volunteers. Data were acquired at three levels of the descending aorta. Thirty percent reduction in diastolic cross sectional area was observed in the caudal direction between these levels. Total blood flow (ml/min) in the abdominal aorta at the three sites was 4094 1600, 2339 910 and 1602 549 respectively. Flows in the coeliac trunk, superior mesenteric artery and renal arteries were also calculated. The net flow in the abdominal aorta above the coeliac trunk was persistently forward, while there was considerable backflow (13% of total instantaneous flow) below the renal arteries during early diastole. Magnetic resonance imaging is a non-invasive technique for quantitative assessment of blood flow in the abdominal aorta and its main branches.
European Radiology 11/1992; 2(6):559-564. · 3.22 Impact Factor
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ABSTRACT: This study was designed to investigate the value of noninvasive imaging modalities for the detection of obstruction in extracardiac ventriculopulmonary conduits.
the diagnosis of obstruction in a conduit by noninvasive methods can be difficult. Obstruction may be silent and its progression unnoticed. Nuclear magnetic resonance imaging (NMR) with velocity mapping is a new noninvasive technique that can provide high resolution images and has been shown to be a reliable method of measuring blood flow velocity.
Two-dimensional echocardiography, pulsed wave Doppler echocardiography and NMR spin echo imaging were used in 52 patients with an extracardiac ventriculopulmonary conduit. Continuous wave Doppler echocardiography was used in 30 of these, Doppler color flow mapping in 26 and NMR velocity mapping in 12. Cardiac catheterization data were available in 27 patients and operative or autopsy findings in 11.
The conduit could be assessed by two-dimensional and pulsed wave Doppler echocardiography in only 17% of patients. Doppler color flow and continuous wave echocardiography provided technically satisfactory data in 19% and 83%, respectively. The anatomy of the conduit was adequately displayed by NMR imaging in 90%. A minimal diameter less than 18 mm indicated conduit obstruction, although failure to detect calcification resulted in obstruction being missed in some patients. Calculated gradients in obstructed conduits derived from NMR velocity mapping correlated well with results of continuous wave Doppler echocardiography and gave an accurate localization of the site of obstruction as well as a measure of its severity.
NMR imaging with velocity mapping is the most effective noninvasive method of assessing obstruction in ventriculopulmonary conduits and can obviate the need for invasive investigation before an interventional procedure is performed.
Journal of the American College of Cardiology 09/1992; 20(2):338-44. · 14.16 Impact Factor
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ABSTRACT: Cine magnetic resonance imaging (MRI) provides a tomographic method of assessing regional ventricular function in any desired plane. It has not been possible to obtain adequate images during dynamic exercise, and this has limited its value in patients with coronary artery disease (CAD). Therefore, an infusion of dobutamine was used to study 25 patients with exertional chest pain and abnormal exercise electrocardiograms. Areas of abnormal wall motion were compared with areas of abnormal myocardial perfusion imaged by dobutamine thallium emission tomography and with coronary arteriography. Twenty-two patients had significant CAD. Twenty-one (96%) of these patients had reversible myocardial ischemia shown by dobutamine thallium tomography, and 20 (91%) had reversible wall motion abnormalities shown by dobutamine MRI. Comparison of abnormal segments of perfusion and wall motion showed 96% agreement at rest, 90% agreement during stress, and 91% agreement for the assessment of functional reversibility. The normalized magnetic resonance signal intensity of the ischemic segments showed a small but significant reduction when compared with that of normal segments (-67 units [9.2%]; p less than 0.05). Dobutamine infusion was well-tolerated, despite causing chest discomfort in 24 patients (96%). Nine patients (36%) developed a minor dysrhythmia that was usually ventricular premature complexes, but this did not limit infusion, and other side effects were mild. The short plasma half-life of dobutamine makes it ideal as a stress agent for imaging techniques (such as MRI), and these results suggest that it is more effective in the provocation of wall motion abnormalities than is dipyridamole in patients with CAD.
The American Journal of Cardiology 08/1992; 70(1):34-40. · 3.37 Impact Factor
