Dark-rim Artifacts Research Articles

Retrospective Detection and Suppression of Dark-Rim Artifacts in First-Pass Perfusion Cardiac MRI Enabled by Deep Learning.

The dark-rim artifact (DRA) remains an important challenge in the routine clinical use of first-pass perfusion (FPP) cardiac magnetic resonance imaging (cMRI). The DRA mimics the appearance of perfusion defects in the subendocardial wall and reduces the accuracy of diagnosis in patients with suspected ischemic heart disease. The main causes for DRA are known to be Gibbs ringing and bulk motion of the heart. The goal of this work is to propose a deep-learning-enabled automatic approach for the detection of motion-induced DRAs in FPP cMRI datasets. To this end, we propose a new algorithm that can detect the DRA in individual time frames by analyzing multiple reconstructions of the same time frame (k-space data) with varying temporal windows. In addition to DRA detection, our approach is also capable of suppressing the extent and severity of DRAs as a byproduct of the same reconstruction-analysis process. In this proof-of-concept study, our proposed method showed a good performance for automatic detection of subendocardial DRAs in stress perfusion cMRI studies of patients with suspected ischemic heart disease. To the best of our knowledge, this is the first approach that performs deep-learning-enabled detection and suppression of DRAs in cMRI.Clinical Relevance- Our approach enables clinicians to provide a more accurate diagnosis of ischemic heart disease by detecting and suppressing subendocardial dark-rim artifacts in first-pass perfusion cMRI datasets.

Influence of motion correction on the visual analysis of cardiac magnetic resonance stress perfusion imaging.

Image post-processing corrects for cardiac and respiratory motion (MoCo) during cardiovascular magnetic resonance (CMR) stress perfusion. The study analyzed its influence on visual image evaluation. Sixty-two patients with (suspected) coronary artery disease underwent a standard CMR stress perfusion exam during free-breathing. Image post-processing was performed without (non-MoCo) and with MoCo (image intensity normalization; motion extraction with iterative non-rigid registration; motion warping with the combined displacement field). Images were evaluated regarding the perfusion pattern (perfusion deficit, dark rim artifact, uncertain signal loss, and normal perfusion), the general image quality (non-diagnostic, imperfect, good, and excellent), and the reader's subjective confidence to assess the images (not confident, confident, very confident). Fifty-three (non-MoCo) and 52 (MoCo) myocardial segments were rated as 'perfusion deficit', 113 vs. 109 as 'dark rim artifacts', 9 vs. 7 as 'uncertain signal loss', and 817 vs. 824 as 'normal'. Agreement between non-MoCo and MoCo was high with no diagnostic difference per-patient. The image quality of MoCo was rated more often as 'good' or 'excellent' (92 vs. 63%), and the diagnostic confidence more often as "very confident" (71 vs. 45%) compared to non-MoCo. The comparison of perfusion images acquired during free-breathing and post-processed with and without motion correction demonstrated that both methods led to a consistent evaluation of the perfusion pattern, while the image quality and the reader's subjective confidence to assess the images were rated more favorably for MoCo.

Quantification of Myocardial Blood Flow by Machine Learning Analysis of Modified Dual Bolus MRI Examination

Contrast-enhanced magnetic resonance imaging (MRI) is a promising method for estimating myocardial blood flow (MBF). However, it is often affected by noise from imaging artefacts, such as dark rim artefact obscuring relevant features. Machine learning enables extracting important features from such noisy data and is increasingly applied in areas where traditional approaches are limited. In this study, we investigate the capacity of machine learning, particularly support vector machines (SVM) and random forests (RF), for estimating MBF from tissue impulse response signal in an animal model. Domestic pigs (n = 5) were subjected to contrast enhanced first pass MRI (MRI-FP) and the impulse response at different regions of the myocardium (n = 24/pig) were evaluated at rest (n = 120) and stress (n = 96). Reference MBF was then measured using positron emission tomography (PET). Since the impulse response may include artefacts, classification models based on SVM and RF were developed to discriminate noisy signal. In addition, regression models based on SVM, RF and linear regression (for comparison) were developed for estimating MBF from the impulse response at rest and stress. The classification and regression models were trained on data from 4 pigs (n = 168) and tested on 1 pig (n = 48). Models based on SVM and RF outperformed linear regression, with higher correlation (RSVM2 = 0.81, RRF2 = 0.74, Rlinear_regression2 = 0.60; ρSVM = 0.76, ρRF = 0.76, ρlinear_regression = 0.71) and lower error (RMSESVM = 0.67 mL/g/min, RMSERF = 0.77 mL/g/min, RMSElinear_regression = 0.96 mL/g/min) for predicting MBF from MRI impulse response signal. Classifier based on SVM was optimal for detecting impulse response signals with artefacts (accuracy = 92%). Modified dual bolus MRI signal, combined with machine learning, has potential for accurately estimating MBF at rest and stress states, even from signals with dark rim artefacts. This could provide a protocol for reliable and easy estimation of MBF, although further research is needed to clinically validate the approach.

Comparability of compressed sensing-based gradient echo perfusion sequence SPARSE and conventional gradient echo sequence in assessment of myocardial ischemia

PurposeStress perfusion imaging plays a major role in non-invasive detection of coronary artery disease.We compared a compressed sensing-based and a conventional gradient echo perfusion sequence with regard to image quality and diagnostic performance. MethodPatients sent for coronary angiography due to pathologic stress perfusion CMR were recruited. All patients underwent two adenosine stress CMR using conventional TurboFLASH and prototype SPARSE sequence as well as quantitative coronary angiography with fractional flow reserve (FFR) within 6 weeks. Coronary angiography was considered gold standard with FFR < 0.75 or visual stenosis >90 % for identification of myocardial ischemia. Diagnostic performance of perfusion imaging was assessed in basal, mid-ventricular and apical slices by quantification of myocardial perfusion reserve (MPR) analysis utilizing the signal upslope method and a deconvolution technique using the fermi function model. Results23 patients with mean age of 69.6 ± 8.9 years were enrolled. 46 % were female.Image quality was similar in conventional TurboFLASH sequence and SPARSE sequence (2.9 ± 0.5 vs 3.1 ± 0.7, p = 0,06). SPARSE sequence showed higher contrast-to-noise ratio (52.1 ± 27.4 vs 40.5 ± 17.6, p < 0.01) and signal-to-noise ratio (15.6 ± 6.2 vs 13.2 ± 4.2, p < 0.01) than TurboFLASH sequence. Dark-rim artifacts occurred less often with SPARSE (9 % of segments) than with TurboFLASH (23 %).In visual assessment of perfusion defects, SPARSE sequence detected less false-positive perfusion defects (n = 1) than TurboFLASH sequence (n = 3).Quantitative perfusion analysis on segment basis showed equal detection of perfusion defects for TurboFLASH and SPARSE with both upslope MPR analysis (TurboFLASH 0.88 ± 0.18; SPARSE 0.77 ± 0.26; p = 0.06) and fermi function model (TurboFLASH 0.85 ± 0.24; SPARSE 0.76 ± 0.30; p = 0.13). ConclusionsCompressed sensing perfusion imaging using SPARSE sequence allows reliable detection of myocardial ischemia.

Perceived Dark Rim Artifact in First-Pass Myocardial Perfusion Magnetic Resonance Imaging Due to Visual Illusion.

To demonstrate that human visual illusion can contribute to sub-endocardial dark rim artifact in contrast-enhanced myocardial perfusion magnetic resonance images. Numerical phantoms were generated to simulate the first-passage of contrast agent in the heart, and rendered in conventional gray scale as well as in color scale with reduced luminance variation. Cardiac perfusion images were acquired from two healthy volunteers, and were displayed by the same gray and color scales used in the numerical study. Before and after k-space windowing, the left ventricle (LV)-myocardium boarders were analyzed visually and quantitatively through intensity profiles perpendicular the boarders. k-space windowing yielded monotonically decreasing signal intensity near the LV-myocardium boarder in the phantom images, as confirmed by negative finite difference values near the board ranging -1.07 to -0.14. However, the dark band still appears, which is perceived by visual illusion. Dark rim is perceived in the in-vivo images after k-space windowing that removed the quantitative signal dip, suggesting that the perceived dark rim is a visual illusion. The perceived dark rim is stronger at peak LV enhancement than the peak myocardial enhancement, due to the larger intensity difference between LV and myocardium. In both numerical phantom and in-vivo images, the illusory dark band is not visible in the color map due to reduced luminance variation. Visual illusion is another potential cause of dark rim artifact in contrast-enhanced myocardial perfusion MRI as demonstrated by illusory rim perceived in the absence of quantitative intensity undershoot.

Fully quantitative pixel-wise analysis of cardiovascular magnetic resonance perfusion improves discrimination of dark rim artifact from perfusion defects associated with epicardial coronary stenosis

BackgroundDark rim artifacts in first-pass cardiovascular magnetic resonance (CMR) perfusion images can mimic perfusion defects and affect diagnostic accuracy for coronary artery disease (CAD). We evaluated whether quantitative myocardial blood flow (MBF) can differentiate dark rim artifacts from true perfusion defects in CMR perfusion.MethodsRegadenoson perfusion CMR was performed at 1.5 T in 76 patients. Significant CAD was defined by quantitative invasive coronary angiography (QCA) ≥ 50% diameter stenosis. Non-significant CAD (NonCAD) was defined as stenosis by QCA < 50% diameter stenosis or computed tomographic coronary angiography (CTA) < 30% in all major epicardial arteries. Dark rim artifacts had study specific and guideline-based definitions for comparison purposes. MBF was quantified at the pixel-level and sector-level.ResultsIn a NonCAD subgroup with dark rim artifacts, stress MBF was lower in the subendocardial than midmyocardial and epicardial layers (2.17 ± 0.61 vs. 3.06 ± 0.75 vs. 3.24 ± 0.80 mL/min/g, both p < 0.001) and was also 30% lower than in remote regions (2.17 ± 0.61 vs. 2.83 ± 0.67 mL/min/g, p < 0.001). However, subendocardial stress MBF in dark rim artifacts was 37–56% higher than in true perfusion defects (2.17 ± 0.61 vs. 0.95 ± 0.43 mL/min/g, p < 0.001). Absolute stress MBF differentiated CAD from NonCAD with an accuracy ranging from 86 to 89% (all p < 0.001) using pixel-level analyses. Similar results were seen at a sector level.ConclusionQuantitative stress MBF is lower in dark rim artifacts than remote myocardium but significantly higher than in true perfusion defects. If confirmed in larger series, this approach may aid the interpretation of clinical stress perfusion exams.Trial registrationClinicalTrials.gov Identifier: NCT00027170; first posted 11/28/2001; updated 11/27/2017.

Simultaneous multi slice (SMS) balanced steady state free precession first-pass myocardial perfusion cardiovascular magnetic resonance with iterative reconstruction at 1.5\xa0T

BackgroundSimultaneous-Multi-Slice (SMS) perfusion imaging has the potential to acquire multiple slices, increasing myocardial coverage without sacrificing in-plane spatial resolution. To maximise signal-to-noise ratio (SNR), SMS can be combined with a balanced steady state free precession (bSSFP) readout. Furthermore, application of gradient-controlled local Larmor adjustment (GC-LOLA) can ensure robustness against off-resonance artifacts and SNR loss can be mitigated by applying iterative reconstruction with spatial and temporal regularisation. The objective of this study was to compare cardiovascular magnetic resonance (CMR) myocardial perfusion imaging using SMS bSSFP imaging with GC-LOLA and iterative reconstruction to 3 slice bSSFP.MethodsTwo contrast-enhanced rest perfusion sequences were acquired in random order in 8 patients: 6-slice SMS bSSFP and 3 slice bSSFP. All images were reconstructed with TGRAPPA. SMS images were also reconstructed using a non-linear iterative reconstruction with L1 regularisation in wavelet space (SMS-iter) with 7 different combinations for spatial (λσ) and temporal (λτ) regularisation parameters. Qualitative ratings of overall image quality (0 = poor image quality, 1 = major artifact, 2 = minor artifact, 3 = excellent), perceived SNR (0 = poor SNR, 1 = major noise, 2 = minor noise, 3 = high SNR), frequency of sequence related artifacts and patient related artifacts were undertaken. Quantitative analysis of contrast ratio (CR) and percentage of dark rim artifact (DRA) was performed.ResultsAmong all SMS-iter reconstructions, SMS-iter 6 (λσ 0.001 λτ 0.005) was identified as the optimal reconstruction with the highest overall image quality, least sequence related artifact and higher perceived SNR. SMS-iter 6 had superior overall image quality (2.50 ± 0.53 vs 1.50 ± 0.53, p = 0.005) and perceived SNR (2.25 ± 0.46 vs 0.75 ± 0.46, p = 0.010) compared to 3 slice bSSFP. There were no significant differences in sequence related artifact, CR (3.62 ± 0.39 vs 3.66 ± 0.65, p = 0.88) or percentage of DRA (5.25 ± 6.56 vs 4.25 ± 4.30, p = 0.64) with SMS-iter 6 compared to 3 slice bSSFP.ConclusionsSMS bSSFP with GC-LOLA and iterative reconstruction improved image quality compared to a 3 slice bSSFP with doubled spatial coverage and preserved in-plane spatial resolution. Future evaluation in patients with coronary artery disease is warranted.

First-pass myocardial perfusion MRI with reduced subendocardial dark-rim artifact using optimized Cartesian sampling.

The presence of subendocardial dark-rim artifact (DRA) remains an ongoing challenge in first-pass perfusion (FPP) cardiac magnetic resonance imaging (MRI). We propose a free-breathing FPP imaging scheme with Cartesian sampling that is optimized to minimize the DRA and readily enables near-instantaneous image reconstruction. The proposed FPP method suppresses Gibbs ringing effects-a major underlying factor for the DRA-by "shaping" the underlying point spread function through a two-step process: 1) an undersampled Cartesian sampling scheme that widens the k-space coverage compared to the conventional scheme; and 2) a modified parallel-imaging scheme that incorporates optimized apodization (k-space data filtering) to suppress Gibbs-ringing effects. Healthy volunteer studies (n = 10) were performed to compare the proposed method against the conventional Cartesian technique-both using a saturation-recovery gradient-echo sequence at 3T. Furthermore, FPP imaging studies using the proposed method were performed in infarcted canines (n = 3), and in two symptomatic patients with suspected coronary microvascular dysfunction for assessment of myocardial hypoperfusion. Width of the DRA and the number of DRA-affected myocardial segments were significantly reduced in the proposed method compared to the conventional approach (width: 1.3 vs. 2.9 mm, P < 0.001; number of segments: 2.6 vs. 8.7; P < 0.0001). The number of slices with severe DRA was markedly lower for the proposed method (by 10-fold). The reader-assigned image quality scores were similar (P = 0.2), although the quantified myocardial signal-to-noise ratio was lower for the proposed method (P < 0.05). Animal studies showed that the proposed method can detect subendocardial perfusion defects and patient results were consistent with the gold-standard invasive test. The proposed free-breathing Cartesian FPP imaging method significantly reduces the prevalence of severe DRAs compared to the conventional approach while maintaining similar resolution and image quality. 2 J. Magn. Reson. Imaging 2017;45:542-555.

All-systolic non-ECG-gated myocardial perfusion MRI: Feasibility of multi-slice continuous first-pass imaging.

To develop and test the feasibility of a new method for non-ECG-gated first-pass perfusion (FPP) cardiac MR capable of imaging multiple short-axis slices at the same systolic cardiac phase. A magnetization-driven pulse sequence was developed for non-ECG-gated FPP imaging without saturation-recovery preparation using continuous slice-interleaved radial sampling. The image reconstruction method, dubbed TRACE, used self-gating based on reconstruction of a real-time image-based navigator combined with reference-constrained compressed sensing. Data from ischemic animal studies (n = 5) was used in a simulation framework to evaluate temporal fidelity. Healthy subjects (n = 5) were studied using both the proposed approach and the conventional method to compare the myocardial contrast-to-noise ratio (CNR). Patients (n = 2) underwent adenosine stress studies using the proposed method. Temporal fidelity of the developed method was shown to be sufficient at high heart-rates. The healthy volunteers studies demonstrated normal perfusion and no dark-rim artifacts. Compared with the conventional scheme, myocardial CNR for the proposed method was slightly higher (8.6 ± 0.6 versus 8.0 ± 0.7). Patient studies showed stress-induced perfusion defects consistent with invasive angiography. The presented methods and results demonstrate feasibility of the proposed approach for high-resolution non-ECG-gated FPP imaging of 3 myocardial slices at the same systolic phase, and indicate its potential for achieving desirable image quality (high CNR and no dark-rim artifacts).

Patient adaptive maximal resolution magnetic resonance myocardial stress perfusion imaging.

To demonstrate the feasibility of an automatic adaptive acquisition sequence. Magnetic resonance perfusion pulse sequences often leave potential acquisition time unused in patients with lower heart-rates (HR) and smaller body size. A perfusion technique was developed that automatically adapts to HR and field-of-view by maximizing in-plane spatial resolution while maintaining temporal resolution every cardiac cycle. Patients (n = 10) and volunteers (n = 10) were scanned with both a standard resolution and adaptive method. Image quality was scored, signal-to-noise ratio (SNR) calculated, and width of dark-rim artifact (DRA) measured. The acquired spatial resolution of the adaptive sequence (1.92 × 1.92 mm(2) ± 0.34) was higher than the standard resolution (2.42 × 2.42 mm(2) ) (P < 0.0001). Mean DRA width was reduced using the adaptive pulse sequence (1.94 ± 0.60 mm vs. 2.82 ± 0.65 mm, P < 0.0001). The signal-to-noise ratio (SNR) was higher with the standard pulse sequence (6.7 ± 2.2 vs. 3.8 ± 1.8, P < 0.0001). There was no difference in image quality score between sequences in either volunteers (1.1 ± 0.31 vs. 1.0 ± 0.0, P = 0.34) or patients (1.3 ± 0.48 vs. 1.3 ± 0.48, P = 1.0). Optimizing the use of available imaging time during first-pass perfusion with a magnetic resonance imaging pulse sequence that adapts image acquisition duration to HR and patient size is feasible. Acquired in-plane spatial resolution is improved, the DRA is reduced, and while SNR is reduced with the adaptive sequence consistent with the lower voxel size used, image quality is maintained.

Through-plane dark-rim artefacts in 3D first-pass myocardial perfusion

Background The dark-rim artefact (DRA) is well known in 2D firstpass perfusion (FPP). The in-plane features of DRA are understood, but DRA has not been examined along the second phase-encoding (partition) direction for 3D FPP. The Gibbs contribution to DRAs in 2D FPP is minimised by finer resolution, but low through-plane resolutions of 3D FPP imply risk of partition axis DRAs. We investigated these new partition DRAs (PDRAs”) and partial volume effects due to coarse resolution of this direction.

First-pass perfusion CMR with reduced dark-rim artifact and instantaneous image reconstruction using optimized cartesian sampling and apodization

Background Subendocardial dark-rim artifact (DRA) continues to be a major issue that limits the diagnostic performance of first pass perfusion (FPP) CMR. Non-Cartesian approaches such as radial or spiral acquisition have been proposed to minimize DRAs. Among these approaches, those that can operate without the need for breath-holding typically require a time-consuming offline image reconstruction procedure, which limits their clinical accessibility. We propose a free-breathing DRA-reduced FPP scheme with instant image reconstruction on the scanner.

Adenosine stress cardiovascular magnetic resonance with variable-density spiral pulse sequences accurately detects coronary artery disease: initial clinical evaluation.

Adenosine stress cardiovascular magnetic resonance perfusion imaging can be limited by motion-induced dark-rim artifacts, which may be mistaken for true perfusion abnormalities. A high-resolution variable-density spiral pulse sequence with a novel density compensation strategy has been shown to reduce dark-rim artifacts in first-pass perfusion imaging. We aimed to assess the clinical performance of adenosine stress cardiovascular magnetic resonance using this new perfusion sequence to detect obstructive coronary artery disease. Cardiovascular magnetic resonance perfusion imaging was performed during adenosine stress (140 μg/kg per minute) and at rest on a Siemens 1.5-T Avanto scanner in 41 subjects with chest pain scheduled for coronary angiography. Perfusion images were acquired during injection of 0.1 mmol/kg Gadolinium-diethylenetriaminepentacetate at 3 short-axis locations using a saturation recovery interleaved variable-density spiral pulse sequence. Significant stenosis was defined as >50% by quantitative coronary angiography. Two blinded reviewers evaluated the perfusion images for the presence of adenosine-induced perfusion abnormalities and assessed image quality using a 5-point scale (1 [poor] to 5 [excellent]). The prevalence of obstructive coronary artery disease by quantitative coronary angiography was 68%. The average sensitivity, specificity, and accuracy were 89%, 85%, and 88%, respectively, with a positive predictive value and negative predictive value of 93% and 79%, respectively. The average image quality score was 4.4±0.7, with only 1 study with more than mild dark-rim artifacts. There was good inter-reader reliability with a κ statistic of 0.67. Spiral adenosine stress cardiovascular magnetic resonance results in high diagnostic accuracy for the detection of obstructive coronary artery disease with excellent image quality and minimal dark-rim artifacts.

129 Automatic Maximal Resolution Heart Rate Adaptive Stress Perfusion Imaging: Cardiovascular Magnetic Resonance Study at 3.0T

IntroductionMyocardial perfusion cardiovascular magnetic resonance (CMR) with vasodilator stress has high diagnostic accuracy for the detection of coronary artery disease (CAD). Current CMR perfusion pulse sequences use fixed acquisition parameters...

Dark-rim-free ungated first-pass perfusion CMR with 3-Slice end-systolic imaging: initial experience

Background First-pass perfusion (FPP) cardiac MR (CMR) imaging has been shown to have a high performance for diagnosis of coronary artery disease (CAD). Reliability of FPP imaging, however, is hindered by dark-rim artifacts (DRAs) and the need for near-perfect ECG gating. The latter can be challenging in the presence of arrhythmias or heart-rate variations during stress. Moreover, endsystolic (ES) imaging has recently been shown to provide improved visualization of subendocardial defects [1]. We developed an innovative ungated FPP technique capable of simultaneously eliminating DRAs [2,3] and enabling reconstruction of all slices at ES. We hypothesized that the developed method achieves DRA-free imaging and high accuracy in patients with suspected CAD, using nuclear myocardial perfusion imaging (MPI) as the reference. Methods Based on the so-called “Ungated Cine FPP” approach [4], a multi-slice magnetization-driven [5-7] method was developed for ungated FPP imaging. Figure 1 highlights the main differences of the proposed pulse sequence compared with the conventional FPP method. All scans were performed on a 3T clinical scanner using an ungated RF-spoiled GRE sequence with continuous golden-angle radial acquisition as in Figure 1b (flip angle = 21°, resolution: 1.7 × 1.7 × 10 mm). The reconstruction method used automatic self-gating and optimally apodized [3] compressed sensing for DRA-free accelerated reconstruction. Normal subjects (n = 6) were studied using both the proposed and conventional methods. Patients (n = 9) with suspected CAD on the basis of recent abnormal SPECT/PET MPI underwent adenosine stress/rest FFP CMR. Three patients returned for a second study using the conventional method. Results The ungated FPP studies in normal subjects were all of high quality and demonstrated normal perfusion. A representative patient study is shown in Figure 2. Stressinduced hypoperfusion was observed in the ES Ungated Cine FPP images, corresponding to a reversible defect on PET MPI (Figure 2b). Figure 2c shows the mid slice for the conventional FPP scan. Based on nuclear MPI studies, sensitivity and specificity of the developed method were 93% and 95%, respectively. The minor disagreements can be explained by the presence of subendocardial defects and possible artifacts on SPECT. All images were reviewed and no DRAs was detected on the Ungated Cine FPP images (2 readers, consensus). However, for the 3 studies using the conventional method, mild-moderate DRA was observed in 21% of the segments. Conclusions Conventional FPP methods are prone to DRAs, require accurate ECG gating, and do not provide the freedom to image all slices at ES. The developed method overcomes these challenges and is an attractive alternative with the advantage of simplicity (no gating), higher accuracy in the subendocardium (no DRAs, ES imaging), and thereby potentially improved reliability. Preliminary results in healthy volunteers and patients with suspected CAD were of high quality and showed high accuracy compared to nuclear MPI.

Adenosine stress CMR with variable density spiral pulse sequences accurately detects CAD with minimal dark-rim artifacts

Background Adenosine stress CMR perfusion imaging has numerous advantages over competing modalities for assessing CAD demonstrating high diagnostic and prognostic utility. However, adenosine stress CMR perfusion imaging is limited by motion-induced dark-rim artifacts (DRA) which may be mistaken for true perfusion abnormalities. We have previously demonstrated that a high-resolution variable-density spiral pulse sequence with a novel density compensation strategy reduces ringing artifacts in firstpass perfusion imaging. The purpose of this study was to assess the clinical performance of this new technique to detect obstructive coronary artery disease (CAD).

Towards elimination of the dark-rim artifact in first-pass myocardial perfusion MRI: removing Gibbs ringing effects using optimized radial imaging.

Subendocardial dark-rim artifacts (DRAs) remain a major concern in first-pass perfusion (FPP) myocardial MRI and may lower the diagnostic accuracy for detection of ischemia. A major source of DRAs is the "Gibbs ringing" effect. We propose an optimized radial acquisition strategy aimed at eliminating ringing-induced DRAs in FPP. By studying the underlying point spread function (PSF), we show that optimized radial sampling with a simple reconstruction method can eliminate the oscillations in the PSF that cause ringing artifacts. We conducted realistic MRI phantom experiments and in vivo studies (n = 12 healthy humans) to evaluate the artifact behavior of the proposed imaging scheme in comparison to a conventional Cartesian imaging protocol. Simulations and phantom experiments verified our theoretical expectations. The in vivo studies showed that optimized radial imaging is capable of significantly reducing DRAs in the early myocardial enhancement phase (during which the ringing effect is most prominent and may obscure perfusion defects) while providing similar resolution and image quality compared with conventional Cartesian imaging. The developed technical framework and results demonstrate that, in comparison to conventional Cartesian techniques, optimized radial imaging with the proposed optimizations significantly reduces the prevalence and spatial extent of DRAs in FPP imaging.

091 QUANTITATIVE THREE-DIMENSIONAL CARDIOVASCULAR MAGNETIC RESONANCE MYOCARDIAL PERFUSION IMAGING IN SYSTOLE AND DIASTOLE AT 3.0 T

Introduction Two-dimensional (2D) perfusion-CMR has been shown to have greater diagnostic accuracy than single-photon emission CT but remains limited by a lack of complete myocardial coverage. Three-dimensional (3D) whole-heart myocardial perfusion CMR addresses this limitation and has recently been shown to be clinically feasible. However, the feasibility and potential clinical utility of quantitative 3D perfusion measurements, as already shown with 2D-perfusion-CMR and positron emission tomography, has yet to be evaluated. The purpose of this study was to establish the feasibility of quantitative 3D-perfusion-CMR to detect coronary artery disease (CAD). Additionally, as 3D-perfusion-CMR offers the opportunity to select the phase of acquisition, a secondary objective was to determine differences between systolic and diastolic estimates of myocardial blood flow (MBF). Methods 35 patients underwent 3D-perfusion-CMR (Philips 3T Achieva TX) with data acquired at both end-systole and mid-diastole (figure 1). Systolic and diastolic perfusion images were analysed in separate reporting sessions in random order. Image quality (0=non-diagnostic, 1=poor, 2=adequate and 3=excellent) and the occurrence of artefact related to respiratory-motion, k-t reconstruction or dark-rim artefact (0=none, 1=mild, 2=moderate and 3=severe) were scored. MBF and myocardial perfusion reserve (MPR) were estimated on a per patient and per territory basis by Fermi function deconvolution. CAD was defined as luminal stenosis ≥70% on quantitative coronary angiography. Results 38 coronary territories had significant CAD. MPR had a high diagnostic accuracy for the detection of CAD, in both systole and diastole (area under curve: 0.92 vs 0.94; p=0.41) (figure 2). At rest, systolic and diastolic MBF estimates were similar—in both normal and diseased territories (no CAD: 1.24±0.15 vs 1.25±0.15 ml/g/min, p=0.27; CAD 1.24±0.15 vs 1.26±0.14 ml/g/min, p=0.20). At stress, diastolic MBF estimates were significantly greater than systolic estimates (no CAD: 3.21±0.50 vs 2.75±0.42 ml/g/min, p Conclusions We have shown that quantitative 3D-perfusion-CMR is feasible and can be used to detect CAD with high diagnostic accuracy. Image quality and less artefact, make systole the preferred phase for acquisition in 3D-perfusion-CMR. Finally, there were significant differences in systolic and diastolic MBF estimates and therefore the phase of acquisition should always be stated in future quantitative studies.

Eliminating dark-rim artifacts in first-pass myocardial perfusion imaging

Background We demonstrate that projection imaging significantly reduces the prevalence and spatial extent of subendocardial dark-rim artifacts (DRAs) in first-pass perfusion (FPP) myocardial MR, compared to conventional Cartesian techniques. A major cause of DRAs, which remain a major concern in FPP imaging, is known to be the socalled Gibbs ringing (truncation) phenomenon [1-3]. Radial k-space sampling exhibits minimal Gibbs effects with typical FPP parameters, thereby eliminating a major contributing factor to DRAs [4]. The underlying theory is demonstrated in Fig. 1, which describes Cartesian and radial k-space sampling (with the same number of readouts) and the corresponding point spread functions (PSFs). Insufficient coverage along phase-encode direction with Cartesian sampling results in significant ringing in image domain (Fig. 1b). In contrast, angular undersampling results in streaks outside of a “local” region for

Improved first‐pass spiral myocardial perfusion imaging with variable density trajectories

To develop and evaluate variable-density spiral first-pass perfusion pulse sequences for improved efficiency and off-resonance performance and to demonstrate the utility of an apodizing density compensation function (DCF) to improve signal-to-noise ratio (SNR) and reduce dark-rim artifact caused by cardiac motion and Gibbs Ringing. Three variable density spiral trajectories were designed, simulated, and evaluated in 18 normal subjects, and in eight patients with cardiac pathology on a 1.5T scanner. By using a DCF, which intentionally apodizes the k-space data, the sidelobe amplitude of the theoretical point spread function (PSF) is reduced by 68%, with only a 13% increase in the full-width at half-maximum of the main-lobe when compared with the same data corrected with a conventional variable-density DCF, and has an 8% higher resolution than a uniform density spiral with the same number of interleaves and readout duration. Furthermore, this strategy results in a greater than 60% increase in measured SNR when compared with the same variable-density spiral data corrected with a conventional DCF (P < 0.01). Perfusion defects could be clearly visualized with minimal off-resonance and dark-rim artifacts. Variable-density spiral pulse sequences using an apodized DCF produce high-quality first-pass perfusion images with minimal dark-rim and off-resonance artifacts, high SNR and contrast-to-noise ratio, and good delineation of resting perfusion abnormalities.