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Biomedical subjects

Raad H Mohiaddin

Publications and source records attributed to Raad H Mohiaddin.

At least 19 recordsLinked to original sources
PubMed2006

3D geometric reconstruction of thoracic aortic aneurysms.

BACKGROUND: The thoracic aortic aneurysm (TAA) is a pathology that involves an expansion of the aortic diameter in the thoracic aorta, leading to risk of rupture. Recent studies have suggested that internal wall stress, which is affected by TAA geometry and the presence or absence of thrombus, is a more reliable predictor of rupture than the maximum diameter, the current clinical criterion. Accurate reconstruction of TAA geometry is a crucial step in patient-specific stress calculations. METHODS: In this work, a novel methodology was developed, which combines data from several sets of magnetic resonance (MR) images with different levels of detail and different resolutions. Two sets of images were employed to create the final model, which has the highest level of detail for each component of the aneurysm (lumen, thrombus, and wall). A reference model was built by using a single set of images for comparison. This approach was applied to two patient-specific TAAs in the descending thoracic aorta. RESULTS: The results of finite element simulations showed differences in stress pattern between the coarse and fine models: higher stress values were found with the coarse model and the differences in predicted maximum wall stress were 30% for patient A and 11% for patient B. CONCLUSION: This paper presents a new approach to the reconstruction of an aneurysm model based on the use of several sets of MR images. This enables more accurate representation of not only the lumen but also the wall surface of a TAA taking account of intraluminal thrombus.

Aortic Aneurysm, Thoracic↗
PubMed2006

Elimination of residual blood flow-related signal in 3D volume-selective TSE arterial wall imaging using velocity-sensitive phase reconstruction.

PURPOSE: To improve 3D volume-selective turbo spin-echo (TSE) arterial wall imaging by introducing velocity phase sensitivity to the sequence. MATERIALS AND METHODS: Slow or recirculating blood may give incomplete nulling in 3D vessel wall imaging, hindering differentiation between arterial wall and lumen. Reconstructed phase images are used to reduce the residual blood signal with postprocessing. A volume-selective 3D TSE (1) sequence with increased velocity sensitivity perpendicular to the slab was developed. Sensitivity was introduced by modifying the gradient waveforms such that residual signal from slow or recirculating blood is distinguished from the wall by the phase shift introduced. This was tested on a pulsatile flow phantom and the carotid artery wall of six healthy volunteers and 17 patients. Images were acquired on a Siemens Magnetom Sonata 1.5T scanner. A quantitative comparison of the lumen/wall contrast was made using images acquired with and without modification. RESULTS: Velocity sensitivity produces significantly reduced residual signal by intravoxel dephasing. Phantom "lumen/tissue" contrast improved by 0.10 (P < 0.01), with a similar change in vivo (0.69-0.73, P < 0.01). Postprocessing removal of the blood signal using phase signal provided further improvement. CONCLUSION: Introducing velocity sensitivity reduces unwanted, potentially misleading residual blood in 3D volume-selective vessel wall imaging.

Adult↗
PubMed2005

Angiosarcoma of the right atrium: a diagnostic dilemma.

Angiosarcomas of the heart are rare and usually fatal. We describe a case where cardiovascular magnetic resonance imaging was crucial in making the diagnosis. Surgical resection was performed and the diagnosis was confirmed by histology.

Female↗
PubMed2005

Applications of phase-contrast flow and velocity imaging in cardiovascular MRI.

A review of cardiovascular clinical and research applications of MRI phase-contrast velocity imaging, also known as velocity mapping or flow imaging. Phase-contrast basic principles, advantages, limitations, common pitfalls and artefacts are described. It can measure many different aspects of the complicated blood flow in the heart and vessels: volume flow (cardiac output, shunt, valve regurgitation), peak blood velocity (for stenosis), patterns and timings of velocity waveforms and flow distributions within heart chambers (abnormal ventricular function) and vessels (pulse-wave velocity, vessel wall disease). The review includes phase-contrast applications in cardiac function, heart valves, congenital heart diseases, major blood vessels, coronary arteries and myocardial wall velocity.

Blood Flow Velocity↗
PubMed2005

Sildenafil versus Endothelin Receptor Antagonist for Pulmonary Hypertension (SERAPH) study.

RATIONALE: Phosphodiesterase type 5 (PDE5) inhibition has been proposed for the treatment for pulmonary arterial hypertension (PAH). OBJECTIVE: This study compared adding sildenafil, a PDE5 inhibitor, to conventional treatment with the current practice of adding bosentan, an endothelin receptor antagonist. METHODS: Twenty-six patients with PAH, idiopathic or associated with connective tissue disease, World Health Organization (WHO) functional class III, were randomized in a double-blind fashion to receive sildenafil (50 mg twice daily for 4 weeks, then 50 mg three times daily) or bosentan (62.5 mg twice daily for 4 weeks, then 125 mg twice daily) over 16 weeks. MEASUREMENTS: Changes in right ventricular (RV) mass (using cardiovascular magnetic resonance), 6-minute walk distance, cardiac function, brain natriuretic peptide, and Borg dyspnea index. MAIN RESULTS: When analyzed by intention to treat, there were no significant differences between the two treatment groups. One patient on sildenafil died suddenly. Patients on sildenafil who completed the protocol showed significant changes from baseline, namely, reductions in RV mass (-8.8 g; 95% confidence interval [CI], -2, -16; n = 13, p = 0.015) and plasma brain natriuretic peptide levels (-19.4 fmol x ml(-1); 95% CI, -5, -34; p = 0.014) and improvements in 6-minute walk distance (114 m; 95% CI, 67, 160; p = 0.0002), cardiac index (0.3 L x min(-1) x m(-2); 95% CI, 0.1, 0.4; p = 0.008), and systolic left ventricular eccentricity index (-0.2; 95% CI, -0.02, -0.37; p = 0.031). Bosentan improved 6-minute walk distance (59 m; 95% CI, 29, 89; n = 12, p = 0.001) and cardiac index (0.3; 95% CI, 0.1, 0.4; p = 0.008). CONCLUSIONS: Sildenafil added to conventional treatment reduces RV mass and improves cardiac function and exercise capacity in patients with PAH, WHO functional class III. Safety monitoring is important until more experience is obtained.

Adult↗
PubMed2005

Interstudy reproducibility of three-dimensional volume-selective fast spin echo magnetic resonance for quantifying carotid artery wall volume.

PURPOSE: To assess the interstudy reproducibility of a three-dimensional volume-selective, fast spin echo (FSE) magnetic resonance technique for the assessment of carotid artery wall volume, which is a marker for total carotid plaque volume. MATERIALS AND METHODS: Interstudy reproducibility was evaluated in 10 subjects with evidence of carotid artery atherosclerotic disease on carotid Doppler ultrasonography. Subjects were scanned twice with an interscan time of one hour to four days. The carotid artery was imaged in cross-section, and the total carotid arterial wall volume (TWV) was calculated by subtraction of the total carotid lumen volume from the total outer carotid vessel volume. RESULTS: The mean carotid TWV for the scans was 741 and 734 mm3, respectively, with no significant difference (mean difference 7 mm3; P = 0.5). The time for each study was approximately 20 minutes. The standard deviation of the differences between the measurements was 33 mm3, yielding an interstudy coefficient of variation of 4.4%. Sample size calculations showed that 16 patients would enable this difference in plaque volume over time to be detected with 80% power at a P value of 0.05. CONCLUSION: Volumetric analysis with CMR of carotid artery plaques using a three-dimensional volume-selective FSE is efficient with good interstudy reproducibility, and is well suited for longitudinal studies of progression of carotid atheroma with reasonable sample sizes.

Aged↗
PubMed2005

Comparison between three-dimensional volume-selective turbo spin-echo imaging and two-dimensional ultrasound for assessing carotid artery structure and function.

PURPOSE: To compare a volume-selective three-dimensional turbo spin echo (TSE) technique with ultrasound (US) for assessing carotid artery wall structure and function. MATERIALS AND METHODS: A three-dimensional volume-selective TSE technique was used to image the carotid artery in 10 healthy subjects and five hypertensive subjects (each of whom were scanned three times while they received different hypertension treatments). Lumen and wall area were measured on MR images. Two-dimensional US measurements of the intima-media thickness (IMT) and lumen diameter were taken in three orientations through a single cross section. The lumen area change over the cardiac cycle was used to determine distension. For validation, a Bland-Altman analysis was used to compare the vessel wall and lumen areas measured by three-dimensional MRI volumes with those obtained by US scans. RESULTS: Agreement between the two methods was found. The mean difference in distension between US and MRI was 1.2% (+/-5.1%). For the wall area measurements, good agreement was shown, but there was a systematic difference due to the visualization of the adventitia by MRI. Both techniques offer an easy way to objectively measure lumen indices. MRI can provide the complete circumference over the length of a vessel, while US is flexible and relatively inexpensive. The application of US is limited, however, when subjects are poorly echogenic. A difference between hypertensive and healthy subjects was found. CONCLUSION: There was a good agreement between MRI and the clinically established two-dimensional US method. The MRI method has the advantage of providing increased vessel coverage, which permits one to assess localized abnormalities without assuming vessel uniformity.

Adult↗
PubMed2005

3D volume-selective turbo spin echo for carotid artery wall imaging with navigator detection of swallowing.

PURPOSE: To improve 3D volume-selective turbo spin echo (TSE) carotid artery wall imaging by incorporating navigators to reduce artifacts caused by swallowing. MATERIALS AND METHODS: Images were acquired on a Siemens Magnetom Sonata 1.5T scanner. 3D volume-selective TSE scans of the carotid arteries were acquired in six healthy volunteers. A cross-pair navigator placed on the back of the tongue was used to detect swallowing and movement. Two swallowing patterns were tested: 1) a single swallow approximately halfway through the scan time, at the center of k(z), and 2) repeated swallowing as often as possible throughout the scan period. Images were acquired with and without navigators for comparison. Signal intensity in the lumen was quantified for the quality of blood suppression, and the clarity of the vessel wall in the common carotid was ranked by four independent blinded observers. RESULTS: In general, lower signal intensity was recorded in the lumen, and decreased blurring and ghosting were observed on scans with navigator control. This reduction in lumen signal intensity signifies an improvement in the black-blood imaging technique. The differences likely reflect the improved double inversion/blood suppression efficiency due to cycles being rejected when the heart rate changed at the point of swallowing, or decreased motional blurring/ghosting of tissue when the navigator is used, or a combination of these two effects. A statistical analysis of image quality showed a significant difference between navigated and non-navigated scans as scored by four independent, blinded observers. For both swallowing patterns, the mean score for the navigator images was on average 0.6 greater than that of non-navigator images (on a scoring scale of 0-5, where 0 = no vessel visible, and 5 = good delineation and blood suppression) and P-values for all observers were less than 0.01. Overall, the central swallow scans were scored higher than the repeated swallow scans. One reason for this may be the fact that the heart rate increased on swallowing, and this often lasted for one or two cardiac cycles after the navigator returned to the normal acceptance position. The effect of the increased heart rate after swallowing is likely to have an effect on double inversion blood suppression efficiency. Therefore, the increased amount of heart rate changes with repeated swallowing may have a greater adverse effect, even if the navigator rejects data views during the swallowing motion. CONCLUSION: The clarity of vessel wall delineation and the apparent efficiency of blood suppression are reduced by swallowing during acquisition. Both motion blurring and quality of blood suppression are factors that can be improved with the use of a navigator accept/reject method.

Artifacts↗
PubMed2005

Spatio-temporal free-form registration of cardiac MR image sequences.

In this paper we present two registration algorithms for the spatio-temporal alignment of cardiac MR image sequences. Both algorithms have the ability to correct spatial misalignment between the images sequences caused by global and local shape differences. In addition, they have the ability to correct temporal misalignment caused by differences in the length of the cardiac cycles and by differences in the dynamic properties of the hearts. The algorithms use a 4D deformable transformation model which is separated into spatial and temporal components. The first registration algorithm optimizes the spatial and temporal transformation models simultaneously, while the second registration algorithm optimizes the temporal transformation component before optimizing the spatial component. For the evaluation of the spatio-temporal registration methods we have acquired 15 MR image sequences from healthy volunteers. The registration methods were quantitatively evaluated by measuring the overlap and surface distance of anatomical regions and qualitatively by visual inspection. The results demonstrate that a significant improvement in the alignment of the image sequences is achieved by the use of the deformable spatio-temporal transformation model. We demonstrate the use of the method for the construction of a probabilistic MR cardiac atlas representing the anatomy and function of a healthy heart.

Algorithms↗
PubMed2004

Role of magnetic resonance angiography in the diagnosis of major aortopulmonary collateral arteries and partial anomalous pulmonary venous drainage.

BACKGROUND: Accurate diagnosis of major aortopulmonary collaterals (MAPCAs) and partial anomalous pulmonary venous drainage (PAPVD) in adult patients with congenital heart disease is important but problematic. Three-dimensional contrast-enhanced magnetic resonance angiography (MRA) provides a minimally invasive technique to allow detailed studies in a single breath-hold. METHODS AND RESULTS: We assessed the role of contrast-enhanced 3D MRA in 29 consecutive adult patients with a diagnosis of MAPCAs (n=16) or PAPVD (n=13) made by echocardiogram, cardiac catheterization, or surgical inspection. MRA was performed with a 3D spoiled gradient-echo technique with intravenous gadolinium-DTPA (0.2 mmol/kg). In both types of pathology, there was excellent correlation between MRA and the cardiac catheterization, echocardiogram, or surgical inspection. Additional information was gained for patients with MAPCAs on confluence and size of pulmonary arteries (n=13 had central arteries), pulmonary artery stenosis (n=3), aneurysmal dilatation of pulmonary artery (n=1), and additional anomalous vascular abnormality (n=3). Shunt assessment, where present (9 of 16), showed patency in all cases (100%). For adults with PAPVD, further information was obtained on drainage origin (n=11). There were no complications. CONCLUSIONS: Contrast-enhanced 3D MRA provides a fast, noninvasive, radiation-free method of accurate and comprehensive diagnosis of MAPCAs and PAPVD in adult patients.

Adolescent↗
PubMed2004

Comparison of spiral and FLASH phase velocity mapping, with and without breath-holding, for the assessment of left and right coronary artery blood flow velocity.

PURPOSE: To develop high temporal resolution coronary artery spiral phase velocity mapping sequences and to compare the results obtained with those from FLASH sequences. MATERIALS AND METHODS: Velocity curves were obtained in eight left and eight right coronary arteries using breath-hold interleaved spiral (BH_SP), free-breathing interleaved spiral (FB_SP), breath-hold segmented FLASH (BH_FL), and free-breathing FLASH (FB_FL) sequences. Spatial resolution, temporal resolution, and acquisition durations (cardiac cycles) were as follows-BH_SP: 0.9 mm x 0.9 mm, 30 msec, 20 cycles; FB_SP: 0.9 mm x 0.9 mm, 42 msec, 100 cycles; BH_FL: 0.9 mm x 1.8 mm, 70 msec (effective), 20 cycles; FB_FL: 0.9 mm x 1.8 mm, 30 msec, 480 cycles. Peak systolic, peak diastolic, and mean velocities were compared between sequences. RESULTS: For left and right arteries, the FB_SP velocity profiles closely followed those from the FB_FL sequence. By comparison, the BH_FL sequence failed to resolve the sharp peaks in the temporal velocity profiles of the right coronary artery, significantly underestimating the peak systolic (88 mm/second vs. 252 mm/second, P < 0.001), peak diastolic (114 mm/second vs. 153 mm/second, P < 0.01), and mean (56 mm/second vs. 93 mm/second, P < 0.001) velocities. For the less mobile left artery, the peak systolic, peak diastolic, and mean velocities were also underestimated by the BH_FL sequence, although this only reached statistical significance for the systolic peak (80 mm/second vs. 135 mm/second, P < 0.01), 142 mm/second vs. 168 mm/second, (P = ns), and 87 mm/second vs. 101 mm/second, (P = ns) respectively. CONCLUSION: We have shown that the FB_SP sequence developed agrees well with the FB_FL sequence, while the study duration is reduced by a factor of 10 for the same spatial resolution. By comparison, the BH_FL sequence underestimates flow velocities, particularly in the more mobile right coronary artery.

Adult↗
PubMed2004

Segmentation of 4D cardiac MR images using a probabilistic atlas and the EM algorithm.

In this paper an automatic atlas-based segmentation algorithm for 4D cardiac MR images is proposed. The algorithm is based on the 4D extension of the expectation maximisation (EM) algorithm. The EM algorithm uses a 4D probabilistic cardiac atlas to estimate the initial model parameters and to integrate a priori information into the classification process. The probabilistic cardiac atlas has been constructed from the manual segmentations of 3D cardiac image sequences of 14 healthy volunteers. It provides space and time-varying probability maps for the left and right ventricles, the myocardium, and background structures such as the liver, stomach, lungs and skin. In addition to using the probabilistic cardiac atlas as a priori information, the segmentation algorithm incorporates spatial and temporal contextual information by using 4D Markov Random Fields. After the classification, the largest connected component of each structure is extracted using a global connectivity filter which improves the results significantly, especially for the myocardium. Validation against manual segmentations and computation of the correlation between manual and automatic segmentation on 249 3D volumes were calculated. We used the 'leave one out' test where the image set to be segmented was not used in the construction of its corresponding atlas. Results show that the procedure can successfully segment the left ventricle (LV) (r = 0.96), myocardium (r = 0.92) and right ventricle (r = 0.92). In addition, 4D images from 10 patients with hypertrophic cardiomyopathy were also manually and automatically segmented yielding a good correlation in the volumes of the LV (r = 0.93) and myocardium (0.94) when the atlas constructed with volunteers is blurred.

Algorithms↗
PubMed2004

Off-frequency tuning error artifact in steady-state free precession cine imaging due to adjacent air-filled bowel.

Identification of common cardiovascular magnetic resonance (CMR) artifacts is important to optimal image acquisition quality and the avoidance of mistaken clinical diagnosis. We describe an off-frequency tuning error artifact observed during rapid steady-state free precession acquisitions in three patients and resulting in a dramatic appearance within the right and left ventricles. These artifacts were associated with large, adjacent air pockets within a loop of bowel or stomach and were eradicated by retuning of the magnetic resonance scanner's frequency. Awareness of this artifact, its cause and correction, should improve diagnostic image quality and avoid clinical diagnostic confusion. This report also heightens the need for a more robust shimming sequence for cardiac studies.

Adult↗
PubMed2004

Analysis of 3-D myocardial motion in tagged MR images using nonrigid image registration.

Tagged magnetic resonance imaging (MRI) is unique in its ability to noninvasively image the motion and deformation of the heart in vivo, but one of the fundamental reasons limiting its use in the clinical environment is the absence of automated tools to derive clinically useful information from tagged MR images. In this paper, we present a novel and fully automated technique based on nonrigid image registration using multilevel free-form deformations (MFFDs) for the analysis of myocardial motion using tagged MRI. The novel aspect of our technique is its integrated nature for tag localization and deformation field reconstruction using image registration and voxel based similarity measures. To extract the motion field within the myocardium during systole we register a sequence of images taken during systole to a set of reference images taken at end-diastole, maximizing the normalized mutual information between the images. We use both short-axis and long-axis images of the heart to estimate the full four-dimensional motion field within the myocardium. We also present validation results from data acquired from twelve volunteers.

Algorithms↗
PubMed2003

Coronary artery bypass graft patency: assessment with true ast imaging with steady-state precession versus gadolinium-enhanced MR angiography.

PURPOSE: To compare the accuracy of multisection true fast imaging with steady-state precession (FISP) with gadolinium-enhanced magnetic resonance (MR) angiography for the detection of coronary artery bypass graft patency. MATERIALS AND METHODS: Twenty-five patients with coronary artery bypass grafts who had recently undergone conventional coronary angiography underwent MR angiography with a 1.5-T system. True FISP angiographic images were acquired in transverse and coronal planes. Coronal cardiac-gated MR angiography was performed with 0.2 mL per kilogram of body weight of gadopentetate dimeglumine injected at a rate of 2 mL/sec. With conventional angiography as the reference standard, the sensitivity, specificity, and accuracy of each technique for the detection of graft patency were determined. Image quality and duration of analysis were determined by two experienced radiologists. RESULTS: In 25 patients, 46 of 56 venous grafts were patent and 22 of 23 arterial grafts were patent. In all grafts at true FISP angiography, sensitivity for patency was 84% (57 of 68 grafts), specificity was 45% (five of 11 grafts), and accuracy was 78% (62 of 79 grafts). At MR angiography, sensitivity was 85% (58 of 68 grafts), specificity was 73% (eight of 11 grafts), and accuracy was 84% (66 of 79 grafts) (difference not significant). Image quality scores were similar with both techniques, but duration of analysis was significantly longer with MR angiography than with true FISP angiography (29 minutes 24 seconds vs 14 minutes 6 seconds, P <.001). CONCLUSION: Accuracy for detection of coronary artery bypass graft patency was similar with gadolinium-enhanced MR angiography and true FISP angiography, with a trend toward more false-positive findings for occlusion and reduced visualization of arterial grafts with true FISP angiography.

Contrast Media↗
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↗