Biomedical subjects

David N Firmin

Publications and source records attributed to David N Firmin.

At least 19 recordsLinked to original sources

PubMed2006

Cardiovascular magnetic resonance in arrhythmogenic right ventricular cardiomyopathy revisited: comparison with task force criteria and genotype.

OBJECTIVES: We sought to assess the utility of cardiovascular magnetic resonance (CMR) in the evaluation of arrhythmogenic right ventricular cardiomyopathy (ARVC) in relation to diagnostic criteria and genotype. BACKGROUND: Timely diagnosis of ARVC is difficult as clinical findings may be subtle and nonspecific in early disease. The role of CMR is controversial owing to the absence of a standardized protocol, insufficient experience with the modality, and inherent difficulties in imaging the right ventricle. METHODS: Comprehensive CMR examination was performed in 232 patients undergoing evaluation for suspected ARVC. CMR outcomes were compared with: 1) prospective clinical diagnosis using Task Force guidelines, with and without the proposed modifications for familial ARVC; and 2) gene-carrier status in 35 individuals from genotyped families. RESULTS: CMR studies were positive in all 64 patients who prospectively fulfilled Task Force criteria, resulting in 100% sensitivity. Specificity in relation to Task Force criteria was low (29%). Of the 119 apparent false positives detected by CMR, however, 63 fulfilled modified diagnostic criteria for familial ARVC and 7 were obligate gene carriers, suggesting that CMR frequently identifies individuals with early disease, in whom Task Force criteria are relatively insensitive. This was borne out by evaluation of genotyped individuals (26 gene-positive and 9 gene-negative), in whom CMR had a sensitivity of 96% and a specificity of 78%. CONCLUSIONS: CMR is a valuable component of the diagnostic workup for ARVC when performed with a dedicated protocol by specialists with experience in analysis of volumes, right ventricular wall motion, and delayed-enhancement imaging.

Adolescent↗

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↗

PubMed2006

Improved turbo spin-echo imaging of the heart with motion-tracking.

PURPOSE: To improve dark-blood and short tau inversion recovery (STIR) prepared turbo spin-echo (TSE) imaging of the heart, particularly in the basal short-axis plane where cardiac misregistration between the preparation and imaging phases is high. MATERIALS AND METHODS: In the first approach (tracked), the basal short-axis plane was labeled and tracked over the cardiac cycle. The slice-selective 180 degrees dark-blood and STIR preparation pulses were then independently positioned on the appropriately timed labeled images. In the second approach (offset), the preparation pulses were output in the same orientation as the imaging plane, but with a user-defined slice offset that was derived from the labeled data. Both approaches were compared with the standard untracked dark-blood STIR TSE sequence (7-mm slice thickness) in 10 healthy volunteers. RESULTS: For typical preparation slice thicknesses, tracked and offset TSE images were superior to the untracked images (both P < 0.01). For the more mobile right ventricle (RV), the image quality of the tracked images was superior to that of the offset images (P < 0.05). CONCLUSION: Tracking the through-plane motion of the heart between preparation and imaging phases improves the quality of thin-slice basal short-axis TSE images, particularly for the more mobile RV.

Algorithms↗

PubMed2006

Development of a novel optimized breathhold technique for myocardial T2 measurement in thalassemia.

PURPOSE: To develop a reproducible fast spin-echo (FSE) technique for accurate myocardial T2 measurement with application to iron overload assessment in thalassemia. MATERIALS AND METHODS: An FSE sequence was developed to permit acquisition of multiple TE images in one breathhold (BH-FSE). A dynamic black-blood scheme was introduced to better cancel blood signal. A nonselective refocusing train was also adopted to suppress stimulated echoes. The optimized technique was tested on phantoms and then applied to 10 normal volunteers and 10 thalassemia patients. Interstudy reproducibility was measured on all the 20 subjects. RESULTS: The mean difference in T2 values was 1.7% from phantom experiments between BH-FSE and the conventional spin-echo (SE) technique. High contrast BH-FSE images were acquired from human subjects, with minimal stimulated echoes and effective blood suppression (P = 0.0005). The coefficient of variation for interstudy reproducibility was 4.3%. T2 values from thalassemia patients were substantially lower than those from the normal subjects (45.2 +/- 26.1 msec vs. 56.9 +/- 8.4 ms, P = 0.02). CONCLUSION: The dynamic black-blood T2 sequence is a fast reproducible acquisition that compares favorably with conventional techniques, is robust to motion artifacts, and yields high blood-myocardium contrast. This technique may provide a useful tool in thalassemia and other scenarios requiring myocardial T2 quantification.

Adolescent↗

PubMed2006

Evaluation of carotid artery wall volume measurement using novel semiautomated analysis software.

PURPOSE: To evaluate semiautomated analysis software for measuring the total carotid arterial wall volume (TWV) as a measure of atheroma burden. MATERIALS AND METHODS: Semiautomated-software and manual analyses of TWV measured by cardiovascular magnetic resonance (CMR) were compared in two phantom models, 10 subjects with no known carotid artery disease, and eight subjects with known carotid disease. The subjects were scanned twice for reproducibility. RESULTS: In subjects with no known carotid disease, semiautomated analysis of 98% of slices showed an improved interstudy coefficient of variation (COV) compared to manual analysis of 50% of slices (4.0% vs. 6.2%, P = 0.02). The proportion of matched cross-sectional slices usable for TWV measurement was superior (99% vs. 49%, P = 0.005) and the median analysis time was shorter (31 minutes vs. 90 minutes, P < 0.001) using the semiautomated software. In subjects with known carotid disease, semiautomated (99% of slices) and manual (56% of slices) analyses had comparable interstudy COVs (4.1% vs. 3.9%, P = 0.01). However, the proportion of matched cross-sectional slices usable for TWV measurement was greater using semiautomated contouring (96% vs. 56%, P = 0.01). CONCLUSION: Carotid CMR measurement of TWV using novel semiautomated analysis software shows good reproducibility, enables greater coverage of arterial vessel wall length, and is considerably faster compared to manual contouring.

Adult↗

PubMed2006

Multi-center validation of the transferability of the magnetic resonance T2* technique for the quantification of tissue iron.

The transferability of the T2* technique for measurement of tissue iron between magnetic resonance (MR) scanners is unknown. Heart and liver multi-breath-hold T2* sequences were installed on MR scanners at six different sites. T2* was assessed locally in five or more patients with thalassemia major (n=39), and subjects were re-scanned at the standardization center in London. Inter-center reproducibility of T2* in heart and liver was 5.0% and 7.1%, with mean absolute differences in T2* of 1.3 ms and 0.45 ms, respectively. The MR multi-breath-hold T2* technique for tissue iron quantification is transferable between scanners with good reproducibility.

Humans↗

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

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

Optimization of the arterial input function for myocardial perfusion cardiovascular magnetic resonance.

PURPOSE: To determine how injection rate, cardiac function, and breathhold influence the arterial input function (AIF), in order to optimize the AIF in the clinical setting for quantitative myocardial perfusion cardiovascular magnetic resonance (CMR). MATERIALS AND METHODS: Gd (0.1 mmol/kg) bolus was injected at 3, 5, or 7 mL/second in 35 patients. In each cardiac cycle during the first-pass, a series of saturation recovery (SR) fast low-angle shot (FLASH) low resolution images with exponentially increasing SR delay times were acquired. Signal intensity (SI) time measurements were made from a region of interest (ROI) drawn in the ascending aorta (AA). The calculation of short T1s and thus peak Gd concentration [Gd] was performed by fitting the mean ROI SI against SR delay times. RESULTS: The mean peak [Gd] in the AA increased as injection rate increased from 3 mL/second (5.0 mM), to 5 mL/second (7.1 mM), to 7 mL/second (4 mM) (P < 0.0001). The peak [Gd] increased as the left ventricular stroke volume (LV SV) increased (P = 0.01). Breath holding was not found to influence peak [Gd]. CONCLUSION: In this study, we found that a high injection rate has advantages over lower injection speeds, although the duration of the AIF was apparently not significantly shortened by faster injection. The choice of expiration or inspiration as breathhold did not have a significant influence upon the AIF. Poor cardiac function was associated with a lower peak [Gd], indicating that first pass perfusion measurements in these patients will be suboptimal.

Aorta↗

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

Intercentre reproducibility of magnetic resonance T2* measurements of myocardial iron in thalassaemia.

In transfusion-dependent thalassemia major, iron-induced cardiomyopathy is the predominant cause of morbidity and mortality. Assessment of myocardial iron loading using MRI gradient echo T2* measurements have been described, but has only been performed at one centre in London. We assessed the transferability of this method by comparing the results from three different MR scanners in three different countries. Ten patients with thalassemia major underwent myocardial T2* assessment using a Siemens Sonata Scanner in London. Patients were also scanned with either a similar T2* sequence on a GE Systems CVI scanner in Athens, or a GE Systems signa echospeed scanner in Cagliari. Two scans were performed at the respective site in all patients to assess interstudy reproducibility at each site. The mean difference and coefficient of variability for the heart between scanners was 0.08 ms and 9.7% between London and Athens; and 0.30 ms and 1.6% between London and Cagliari. The interstudy mean difference and coefficient of variability for the heart in Athens was 0.6 ms and 3.5%, and 0.2 ms and 2.4% in Cagliari. In conclusion, the myocardial iron estimations were consistent between the three centres with scanners of differing manufacture, suggesting that this technique may have widespread application in the assessment of patients with iron overload conditions such as thalassaemia.

Adult↗

PubMed2005

Interstudy reproducibility of quantitative perfusion cardiovascular magnetic resonance.

PURPOSE: To determine the interstudy reproducibility of quantitative first-pass perfusion cardiovascular magnetic resonance with comparison of 2 previously described analysis techniques. There is no published data on the interstudy reproducibility of perfusion cardiovascular magnetic resonance which can be used to determine the significance of longitudinal changes in myocardial perfusion after pharmacologic or therapeutic interventions with defined sample sizes. METHODS: Sixteen subjects (7 normal volunteers, 9 patients with coronary artery disease) had rest and adenosine stress perfusion cardiovascular magnetic resonance studies on two separate visits. A short axis slice was studied on each visit using a fast low-angle shot sequence. The global and regional myocardial perfusion reserve indices were calculated using 2 methods: model based constrained deconvolution with the Fermi function, and normalized upslopes. Reproducibility was defined as the standard deviation of the measurement differences, divided by the mean (coefficient of variation). RESULTS: The reproducibility of global myocardial perfusion reserve indices was 21% in normal volunteers, which was similar to that in patients with coronary artery disease (CAD) (23%, p = .88). The reproducibility of regional myocardial perfusion reserve indices was 28% (p = .45 vs. global analysis). The reproducibility of global MPRi was superior with Fermi deconvolution compared with normalized upslopes (21% vs. 41%, p = .02). CONCLUSION: At this stage of clinical development, the reproducibility of quantitative perfusion cardiovascular magnetic resonance is good, and superior using Fermi deconvolution in preference to upslope analysis.

Adenosine↗

PubMed2005

Comparison of hybrid echo-planar imaging and FLASH myocardial perfusion cardiovascular MR imaging.

The purpose of this study was to compare fast single-shot gradient-echo (FLASH) and hybrid echo-planar imaging (EPI) magnetic resonance (MR) technologies regarding the relative contrast-to-noise ratio (CNR), spatiotemporal resolution, size of inducible perfusion defects, and presence of artifacts in patients with coronary artery disease (CAD). Fifteen patients with CAD underwent rest and adenosine stress gadolinium first-pass perfusion cardiovascular MR examinations with EPI and FLASH. The study was approved by the local ethics committee, and each subject gave written informed consent. The spatial resolution of the two sequences was made similar in nine patients, and the temporal resolution was made similar in six. The images were assessed for CNR, artifact, and size of inducible perfusion defects. The CNR was significantly higher with the EPI sequence, whether matched for spatial (32 vs 22 [46%], P < .001) or temporal (35 vs 23 [51%], P < .001) resolution. There was no significant difference in scoring for artifact or area and transmural extent of inducible perfusion defects with EPI and FLASH, whether matched for temporal or spatial resolution. Further work is warranted to determine the relative diagnostic accuracy of the two techniques.

Aged↗

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

Accurate assessment of the arterial input function during high-dose myocardial perfusion cardiovascular magnetic resonance.

PURPOSE: To develop a method for accurate measurement of the arterial input function (AIF) during high-dose, single-injection, quantitative T1-weighted myocardial perfusion cardiovascular magnetic resonance (CMR). MATERIALS AND METHODS: Fast injection of high-dose gadolinium with highly T1 sensitive myocardial perfusion imaging is normally incompatible with quantitative perfusion modeling because of distortion of the peak of the AIF caused by full recovery of the blood magnetization. We describe a new method that for each cardiac cycle uses a low-resolution short-axis (SA) image with a short saturation-recovery time immediately after the R-wave in order to measure the left ventricular (LV) blood pool signal, which is followed by a single SA high-resolution image with a long saturation-recovery time in order to measure the myocardial signal with high sensitivity. Fifteen subjects were studied. Using the new method, we compared the myocardial perfusion reserve (MPR) with that obtained from the dual-bolus technique (a low-dose bolus to measure the blood pool signal and a high-dose bolus to measure the myocardial signal). RESULTS: A small significant difference was found between MPRs calculated using the new method and the MPRs calculated using the dual-bolus method. CONCLUSION: This new method for measuring the AIF introduced no major error, while removing the practical difficulties of the dual-bolus approach. This suggests that quantification of the MPR can be achieved using the simple high-dose single-bolus technique, which could also image multiple myocardial slices.

Contrast Media↗

PubMed2004

Intra- and interstudy reproducibility of coronary artery diameter measurements in magnetic resonance coronary angiography.

PURPOSE: To determine the intra- and interstudy reproducibility of right coronary artery diameter assessment using serial magnetic resonance (MR) coronary angiography. MATERIALS AND METHODS: Two-dimensional (2D) navigator-gated segmented fast low angle shot (FLASH) images of the proximal right coronary artery were acquired three times in 11 healthy volunteers, the first two times in the same study session and the third time after repositioning the subject in the scanner. Coronary artery diameters were determined using automated segmentation software and intra- and interstudy reproducibility calculated as the standard deviation (SD) of the signed differences between measurements within and between study sessions, respectively. The reproducibility of the segmentation software was determined by repeated analysis of each individual scan. RESULTS: One subject was excluded from the study due to poor-quality images. In the remaining 10 subjects, the mean (+/- SD) intrastudy difference in coronary artery diameters was -0.05 +/- 0.12 mm, a value that is very similar to between-frame (same-film) differences reported in quantitative coronary angiography (QCA). The mean (+/- SD) interstudy difference in coronary artery diameters was 0.16 +/- 0.43 mm, although this was greatly skewed by one subject with poor image plane repositioning. Excluding that subject resulted in a mean (+/- SD) interstudy difference of 0.04 +/- 0.20 mm. The reproducibility of the segmentation software was excellent, with the mean difference between repeat analyses of the images being 0.00 +/- 0.03 mm. CONCLUSION: The intrastudy variability of coronary artery diameter measurements is low, potentially allowing MR coronary angiography to be used as a tool for the noninvasive assessment of serial changes following pharmacological intervention. A major contributing factor to this is the high reproducibility of the segmentation software. Interstudy variability is approximately three times the intrastudy variability.

Adult↗

PubMed2004

Respiratory reordered UNFOLD perfusion imaging.

PURPOSE: To propose a respiratory reordered UNFOLD (RR-UNFOLD) imaging sequence to significantly reduce the amount of k-space data required for first-pass MR myocardial perfusion imaging. MATERIALS AND METHODS: Rapid acquisition of high-resolution imaging data is essential to detailed quantitative analysis of first-pass myocardial perfusion. Existing MR sequences have explored the full capacity of the imaging hardware to reduce the acquisition window within each cardiac cycle while maintaining the desired spatial resolution. Further improvement in perfusion imaging will require a more efficient use of the information content of the k-space data. The method uses prospective diaphragmatic navigator echoes to ensure that temporal filtering of UNFOLD is carried out on a series of images that are spatially registered. An adaptive real-time rebinning algorithm is developed for the creation of static image subseries related to different levels of respiratory motion. Issues concerning the temporal smoothing of tracer kinetic signals are discussed, and a solution based on oversampling of the central k-space is provided. The method is assessed in 10 normal subjects without the administration of contrast agent, and further validated by administration of Gd-DTPA in 10 patients at rest. RESULTS: The results of this study show that RR-UNFOLD significantly extends the applicability of UNFOLD to perfusion imaging, which yields a 40% reduction in image artifact when the same amount of k-space information is used. CONCLUSION: The scan efficiency achieved can be used in combination with MR hardware improvements for extending the three-dimensional spatial coverage and shortening the data acquisition window to provide detailed information on regional myocardial perfusion abnormalities.

Adult↗