Biomedical subjects

David N Firmin

Publications and source records attributed to David N Firmin.

31 records · Page 2Linked to original sources

PubMed2004

Spiral phase velocity mapping of left and right coronary artery blood flow: correction for through-plane motion using selective fat-only excitation.

PURPOSE: To develop a method of correcting both right and left coronary artery flow velocities for the through-plane motion of the vessel, in order to allow details in the temporal flow profiles to be viewed. MATERIALS AND METHODS: The methods developed use selective excitation and velocity mapping of the epicardial fat surrounding the artery, either in a separate acquisition (temporal resolution = 22 msec) or interleaved with the water-excitation acquisition (temporal resolution = 44 msec) used to determine coronary blood flow velocities. The two methods were compared in 10 right and 13 left coronary arteries in healthy volunteers. RESULTS: For the right coronary arteries, correction for through-plane motion significantly reduces the mean systolic flow velocity (75.3 mm/second vs. 90.0 mm/second, P < 0.01), while the mean diastolic flow velocity is unchanged (96.8 mm/second vs. 94.5 mm/second, P = ns). The resulting profiles are biphasic, with approximately equal flow in systole and diastole. For the left arteries, correction for through-plane motion reduces the mean systolic flow velocity (25.0 mm/second vs. 72.8 mm/second, P < 0.001), resulting in the expected diastolic predominant flow profiles. For the right arteries, there were no significant differences in the mean systolic and mean diastolic velocities after correction with the separate fat-excitation acquisition, and after correction the poorer temporal resolution combined water excitation/fat excitation acquisition. However, for the left coronary arteries, the combined water excitation/fat excitation acquisition resulted in a slight reduction in the mean diastolic velocity (121.5 mm/second vs. 130.9 mm/second, P < 0.05). CONCLUSION: Selective excitation of the surrounding epicardial fat enables through-plane correction of both left and right coronary flow velocities, enabling the temporal details of flow velocity to be viewed. With a combined WE/FE acquisition, this can be performed without extending the study duration; however, the reduced temporal resolution and temporal mismatch of the excitations results in a blunting of rapidly changing flow profiles. As such, it may be less suitable for the left coronary artery, which has a greater range of through-plane motion than the right, and correction using separate WE and FE acquisitions, or the adjacent myocardium, may be preferable.

Adult↗

PubMed2004

Combined long- and short-axis myocardial perfusion cardiovascular magnetic resonance.

PURPOSE: To date, myocardial perfusion cardiovascular magnetic resonance (CMR) has been reported in single and multiple short-axis slices. Three short-axis planes can assess 16 segments of the standard 17-segment myocardial model, but this approach fails to assess the ventricular apex that requires at least one long-axis plane. We therefore evaluated the feasibility and benefit of combined long- and short-axis perfusion CMR to enable complete 17 segments coverage for comprehensive myocardial perfusion assessment. METHODS AND MATERIALS: Using a hybrid echo planar imaging (EPI) sequence, we performed rest and adenosine stress first-pass perfusion CMR studies with 3 short-axis (basal, mid, apical) planes, and additional long-axis planes in the same cardiac cycle in a broad range of cardiology patients. RESULTS: Perfusion CMR was performed in 53 consecutive patients using the combined short-long-axis imaging protocol. Twenty-nine of those studied had known or suspected coronary artery disease (CAD), 18 hypertrophic cardiomyopathy, and 6 suspected microvascular perfusion abnormalities. In 39 patients (70%), it was possible to acquire 5 slices at rest and stress including both the horizontal and vertical long axes. In 15 patients (27%), only one long-axis could be acquired, and in 2 patients (5%) only 3 slices (short axis) could be obtained. However, in none of the patients with known or suspected CAD was apical ischemia demonstrated by the long-axis views, despite apical ischemia having been demonstrated with recent SPECT studies in 8 of these patients. CONCLUSION: Rest-stress myocardial perfusion CMR is able to achieve complete segmental coverage of the myocardium using the combined short-long axis approach using an EPI sequence in 97% of a long series of consecutive cardiology patients, while maintaining excellent spatial resolution. However, the long-axis views were not found to be able to demonstrate inducible perfusion defects in the apex.

Adult↗

PubMed2004

Predictive cardiac motion modeling and correction with partial least squares regression.

Respiratory-induced cardiac deformation is a major problem for high-resolution cardiac imaging. This paper presents a new technique for predictive cardiac motion modeling and correction, which uses partial least squares regression to extract intrinsic relationships between three-dimensional (3-D) cardiac deformation due to respiration and multiple one-dimensional real-time measurable surface intensity traces at chest or abdomen. Despite the fact that these surface intensity traces can be strongly coupled with each other but poorly correlated with respiratory-induced cardiac deformation, we demonstrate how they can be used to accurately predict cardiac motion through the extraction of latent variables of both the input and output of the model. The proposed method allows cross-modality reconstruction of patient specific models for dense motion field prediction, which after initial modeling can be used for real-time prospective motion tracking or correction. Detailed numerical issues related to the technique are discussed and the effectiveness of the motion and deformation modeling is validated with 3-D magnetic resonance data sets acquired from ten asymptomatic subjects covering the entire respiratory range.

Algorithms↗

PubMed2003

Coronary artery anomalies: assessment with free-breathing three-dimensional coronary MR angiography.

PURPOSE: To evaluate a simplified protocol by using free-breathing three-dimensional (3D) coronary magnetic resonance (MR) angiography to determine the anatomy of anomalous coronary arteries, in particular the relationship of the vessels to the aortic root. MATERIALS AND METHODS: Twenty-six patients (18 men, eight women; mean age, 50 years; age range, 18-77 years) who had a history of chest pain, palpitations, or syncope and who were suspected of having coronary artery anomalies were examined with free-breathing MR angiography. Multiple 3D volume slabs were acquired at the level of the sinuses of Valsalva by using diaphragmatic navigators for respiratory artifact suppression. The proximal anatomy of the coronary arteries was determined. RESULTS: Six anomalous circumflex arteries originated from the right sinus of Valsalva and passed behind the aortic root. Six right coronary arteries arose from the left sinus of Valsalva and coursed between the aortic root and the right ventricular outflow tract (RVOT). Nine left coronary arteries arose from the right sinus of Valsalva; seven of nine coursed between the aortic root and the RVOT. Five patients had minor anomalies. Overall, in eight patients with anomalous arteries that coursed between the aortic root and the RVOT, conventional coronary angiography could not be used confidently to identify the proximal course. CONCLUSION: Free-breathing 3D coronary MR angiography can be used to identify the proximal anatomy of anomalous coronary arteries.

Adolescent↗

PubMed2003

Volume-selective 3D turbo spin echo imaging for vascular wall imaging and distensibility measurement.

PURPOSE: To use a volume-selective 3D turbo spin echo (TSE) technique to image the carotid artery wall and measure distensibility. MATERIALS AND METHODS: A high-resolution volume-selective 3D TSE sequence has been developed. Volume selection is accomplished by orthogonal gradients for the 90 degrees and 180 degrees excitations and allows a 3D volume of vessel wall to be imaged in a relatively short time. The technique has been developed to allow imaging at any defined phase of the cardiac cycle so that the vascular function and distensibility can be studied. RESULTS: Scan efficiency is increased by the reduced phase encode field of view (FOV) (k(y) steps) by the use of selective volume excitation. Significantly more slices (k(z) phase encode steps) for vessel coverage can be acquired with the same scan time as that of the conventional sequence while maintaining signal-to-noise ratio (SNR) levels. The practical value of the technique was demonstrated on 10 normal subjects with high-resolution vessel distensibility measurements of the carotid arteries. CONCLUSION: A volume-selective TSE method has been used for carotid artery wall imaging and measurement of distensibility in normal subjects. Larger coverage of the vessel, and therefore more information for clinical diagnostics, was achieved with the same overall scan time with an SNR comparable to that of 2D full FOV images.

Adult↗

PubMed2003

A single breath-hold multiecho T2* cardiovascular magnetic resonance technique for diagnosis of myocardial iron overload.

PURPOSE: To assess tissue iron concentrations by the use of a gradient echo T2* multiecho technique. MATERIALS AND METHODS: We compared the results of measurements of heart T2* from 32 patients using the established multiple breath-hold variable TR technique with a new multiecho sequence that acquires all images within a single breath-hold with constant TR. RESULTS: There was good agreement of myocardial T2* values between both methods in the abnormal range of T2* < 20 msec (mean difference 0.2 msec, 95% CI -1.3 to 0.9 msec, r = 0.97, P < 0.0001). The coefficient of variability between the methods was 3.5%. The interstudy reproducibility using the multiecho sequence had a variability coefficient of 2.3% in the abnormal T2* range and 5.8% over all T2* values. There was good agreement between the techniques for the liver T2* values. CONCLUSIONS: The use of the single breath-hold, multiecho acquisition allowed reliable quantification of myocardial T2*. The good reproducibility, speed, and T1 independence of this technique allows greater accuracy, faster patient throughput, and, therefore, reduced costs (which is important in developing countries where thalassemia is most prevalent).

Adolescent↗

PubMed2003

Breath-hold signal-loss sequence for the qualitative assessment of flow disturbances in cardiovascular MR.

PURPOSE: To develop a breath-hold segmented sequence which generates similar patterns of signal loss to a non-breath-hold, relatively long echo time, conventional gradient echo sequence for the qualitative assessment of valvular heart disease. MATERIALS AND METHODS: Both velocity-sensitized and acceleration-sensitized segmented sequences were developed. The sensitivities were empirically adjusted to give similar degrees of signal loss to a conventional sequence. These sequences were compared with a conventional sequence in eight patients with flow disturbances and in four healthy subjects. RESULTS: There was no significant difference in the extent of signal loss observed when using the breath-hold velocity- and acceleration-sensitized sequences developed and the conventional sequence (1862 mm(2), 1831 mm(2), and 1782 mm(2), respectively; P = ns). However, the image quality obtained was significantly better with the breath-hold sequences (both P < 0.01). Furthermore, the image quality achieved with the acceleration-sensitized sequence was significantly better than that achieved with the velocity-sensitized sequence (P < 0.01) where artifacts from beat-to-beat variations in blood-flow velocities were a frequent problem. CONCLUSION: Signal loss in complex flow is best demonstrated using the breath-hold acceleration-sensitized sequence where the signal from both stationary and constant velocity material is rephased at the echo time.

Adult↗

PubMed2003

Interscanner reproducibility of cardiovascular magnetic resonance T2* measurements of tissue iron in thalassemia.

PURPOSE: To assess interscanner reproducibility of tissue iron measurements in patients with thalassemia using gradient echo T2* measurements on two different MRI scanners. MATERIALS AND METHODS: Twenty-five patients with thalassemia major had liver and myocardial T2* assessment using a Picker Edge 1.5T Scanner and a Siemens Sonata 1.5T scanner, with similar gradient echo sequences. In a subset of 13 patients, two scans on the Siemens scanner were performed to assess interstudy reproducibility. RESULTS: There was a highly significant, linear correlation between T2* values obtained for both the heart (r = 0.95) and the liver (r = 0.99) between scanners. The mean difference, coefficient of variability, and 95% confidence intervals between scanners were 0.8 msec, 9.4% and -5.0 to 6.7 msec for the heart; and 0.9 msec, 7.9% and -2.0 to 3.9 msec for the liver. The interstudy mean difference and coefficient of variability on the Siemens scanner was 0.3 msec and 4.8% (r = 0.99) for the heart, and 0.04 msec and 1.9% (r = 0.99) for the liver. CONCLUSION: The T2* technique for measuring tissue iron is reproducible between the two manufacturers' scanners. This suggests that the widespread implementation of the technique is possible for clinical assessment of myocardial iron loading in thalassemia.

Adult↗

PubMed2003

Progress towards patient-specific computational flow modeling of the left heart via combination of magnetic resonance imaging with computational fluid dynamics.

A combined computational fluid dynamics (CFD) and magnetic resonance imaging (MRI) methodology has been developed to simulate blood flow in a subject-specific left heart. The research continues from earlier experience in modeling the human left ventricle using time-varying anatomical MR scans. Breathing artifacts are reduced by means of a MR navigator echo sequence with feedback to the subject, allowing a near constant breath-hold diaphragm position. An improved interactive segmentation technique for the long- and short-axis anatomical slices is used. The computational domain is extended to include the proximal left atrium and ascending aorta as well as the left ventricle, and the mitral and aortic valve orifices are approximately represented. The CFD results show remarkable correspondence with the MR velocity data acquired for comparison purposes, as well as with previously published in vivo experiments (velocity and pressure). Coherent vortex formation is observed below the mitral valve, with a larger anterior vortex dominating the late-diastolic phases. Some quantitative discrepancies exist between the CFD and MRI flow velocities, owing to the limitations of the MR dataset in the valve region, heart rate differences in the anatomical and velocity acquisitions, and to certain phenomena that were not simulated. The CFD results compare well with measured ranges in literature.

Adult↗

PubMed2002

Abnormal subendocardial perfusion in cardiac syndrome X detected by cardiovascular magnetic resonance imaging.

BACKGROUND: In cardiac syndrome X (a syndrome characterized by typical angina, abnormal exercise-test results, and normal coronary arteries), conventional investigations have not found that chest pain is due to myocardial ischemia. Magnetic resonance techniques have higher resolution and therefore may be more sensitive. METHODS: We performed myocardial-perfusion cardiovascular magnetic resonance imaging in 20 patients with syndrome X and 10 matched controls, both at rest and during an infusion of adenosine. Quantitative perfusion analysis was performed by using the normalized upslope of myocardial signal enhancement to derive the myocardial perfusion index and the myocardial-perfusion reserve index (defined as the ratio of the myocardial perfusion index during stress to the index at rest). RESULTS: In the controls, the myocardial perfusion index increased in both myocardial layers with adenosine (in the subendocardium, from a mean [+/-SD] of 0.12+/-0.03 to 0.16+/-0.03 [P=0.02]; in the subepicardium, from 0.11+/-0.02 to 0.17+/-0.05 [P=0.002]); in patients with syndrome X, the myocardial perfusion index did not change significantly in the subendocardium (0.13+/-0.02 vs. 0.14+/-0.03, P=0.11; P=0.09 as compared with controls) but increased in the subepicardium (from 0.11+/-0.02 to 0.20+/-0.04, P<0.001; P=0.11 for the comparison with controls). Adenosine provoked chest pain in 95 percent of patients with syndrome X and 40 percent of controls (P<0.001). CONCLUSIONS: In patients with syndrome X, cardiovascular magnetic resonance imaging demonstrates subendocardial hypoperfusion during the intravenous administration of adenosine, which is associated with intense chest pain. These data support the notion that the chest pain may have an ischemic cause.

Adenosine↗

PubMed2002

Initial experience with the intravascular contrast agent NC100150-injection (Clariscan) for breath-hold and navigator-gated magnetic resonance coronary artery imaging.

PURPOSE: To examine magnetic resonance coronary artery imaging after NC100150-Injection. MATERIALS AND METHODS: Breath-hold and navigator-gated images were acquired in five patients. RESULTS: Breath-hold image quality, coronary artery-fat SDNR, and coronary artery SNR improved. Respiratory artifacts due to reduced liver signal intensity degraded navigator-gated image quality. CONCLUSION: NC100150-Injection improves breath-hold coronary artery imaging. Navigator-gated acquisitions should use techniques that are insensitive to T2* effects.

Aged↗

PubMed2002

Assessment of reactive hyperaemia using real time zonal echo-planar flow imaging.

The measurement of limb blood flow at rest and during reactive hyperaemia has potential as a marker of vascular health and endothelial function because it is the stimulus that causes flow-mediated dilatation, commonly measured as brachial arterial reactivity. Because the flow increases are short lived, they represent a significant challenge for measurement by cardiovascular magnetic resonance. In this study we used a real time, single shot zonal echo-planar imaging method (ZEPI) to study reactive hyperaemia in the femoral artery of five healthy volunteers. Flow velocity was measured every 78 msec. Changes in peak forward flow velocity during systole (580 vs. 390 mm/sec, p < 0.01) and minimum flow velocity (160 vs. 100 mm/sec, p < 0.01) were shown. With progressing improvement in spatial resolution, this technique will allow the accurate noninvasive determination of total flow, flow profile, and peak velocities in real time.

Adult↗

PubMed2002

Morphodynamics of flow through sinuous curvatures of the heart.

Through cardiac looping during embryonic development, human and other vertebrate hearts adopt sinuous curvatures with marked changes in direction of flow at atrial, ventricular and arterial levels. We used magnetic resonance phase velocity mapping to study flow through the hearts of resting volunteers, and Doppler ultrasound to record changes with exercise. We found asymmetric recirculation of blood during filling phases of all four heart cavities, with blood redirected appropriately for onward passage to the next cavity. Doppler traces showed that biphasic ventricular filling became rapid and monophasic on strenuous exercise. We propose that looped curvatures of the heart have fluidic and dynamic advantages. Intra-cavity flow appears to be asymmetric in a manner that preserves stability, and allows momentum of inflowing streams to be redirected towards rather than away from the next cavity. Direction-change at ventricular level is such that recoil away from ejected blood is in a direction that can enhance rather than inhibit ventriculo-atrial coupling. These factors may combine to allow a reciprocating, sling-like, 'morphodynamic' mode of action become effective when heart rate and output increase with exercise. Dynamic efficiency of the looped heart may have favoured evolution of large, complex, active species characteristic of the vertebrate line.

Echocardiography, Doppler, Pulsed↗