POSTER PRESENTATION Open Access Projection imaging of ...
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POSTER PRESENTATION Open Access Projection imaging of myocardial perfusion: minimizing the subendocardial dark-rim artifact Behzad Sharif 1,2* , Rohan Dharmakumar 1,2 , Troy Labounty 1 , Chrisandra Shufelt 1 , Louise Thomson 1 , Noel Bairey Merz 1 , Daniel S Berman 1 , Debiao Li 1,2 From 15th Annual SCMR Scientific Sessions Orlando, FL, USA. 2-5 February 2012 Summary We demonstrate that projection imaging of first-pass myocardial perfusion is robust to a major cause of the so-called subendocardial dark-rim artifact (DRA); thereby proposing radial k-space sampling as the pre- ferred acquisition scheme for DRA-free perfusion imaging. Background Current methods for clinical myocardial perfusion (MP) imaging suffer from image artifacts, specifically the so- called subendocardial dark-rim artifact (DRA) [1-3]. DRAs are especially limiting since they can reduce the sensitivity/specificity of detecting subendocardial MP deficits; hence, eliminating such artifacts remains an active area of research [1]. In this work, we demonstrate that projection imaging of MP is free of Gibbs ringing [2], a major cause of DRAs for conventional schemes. Methods In Cartesian MP MR, Gibbs ringing along the phase- encode (PE) direction leads to DRAs due to an inherent property of the Fourier transform (FT) at sharp signal intensity transitions [2]. However, in projection imaging, the underlying data transform is the Radon transform [4], which does not exhibit the Gibbs ringing in the same form as FT. This fact is demonstrated in Fig. 1 using a numerical simulation. To investigate the validity of this observation in-vivo, healthy canines (N=2) and healthy human volunteers (N=4; IRB approved) were imaged on a clinical 3T scanner (Siemens Verio). Two first-pass MP scans (SR-prepared FLASH) were per- formed at rest (>10 minutes gap) using a single-shot radial (customized) pulse sequence followed by a single- shot Cartesian (product) sequence (common parameters: FOV read = 270-300 mm; BW ≈ 800 Hz/pixel; flip angle = 12; TR = 2.4 ms; TI = 100 ms). Both scans were accel- erated using rate 2 self-calibrating parallel imaging with 36-40 readouts. The customized radial sequence incor- porated gradient delay correction and a 4-fold interleav- ing scheme combined with KWIC processing [5]. Although the readout resolution for the Cartesian scan was higher than the base resolution for the radial scheme (≈1.8 mm vs. ≈2.2 mm), the overall resolution of Cartesian (PE resolution≈2.6 mm) and radial scans were matched to within 10%. Results Fig. 2 shows the reconstruction results for representative dog (a,b) and human (c,d) scans. Each pair of Cartesian/ radial images correspond to the same phase of the con- trast uptake (late-LV/early-myocardial enhancement). As is seen in the figure, Cartesian images (a,c) show DRAs (arrows pointing to hypo-intensities) in the subendocar- dial regions whereas the projection reconstructions (b,d) are free of dark rims (with slightly reduced CNR). Conclusions Recently, a major approach for eliminating the DRAs has been to improve the spatial resolution and thereby reducing Gibbs ringing [1,6]. In this work, we demon- strated that projection imaging is inherently robust to Gibbs ringing. We conclude that an alternative strategy (besides increasing the resolution) is to employ projec- tion imaging (radial trajectories). The presented results were limited to rest scans, although we expect the same properties to hold for stress imaging. However, to match the high resolutions achieved in advanced Carte- sian schemes (e.g., [6]), rate 2 parallel imaging 1 Biomedical Sciences, Biomedical Imaging Research Institute, Cedars-Sinai Medical Center, Los Angeles, CA, USA Full list of author information is available at the end of the article Sharif et al. Journal of Cardiovascular Magnetic Resonance 2012, 14(Suppl 1):P275 http://www.jcmr-online.com/content/14/S1/P275 © 2012 Sharif et al; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Transcript of POSTER PRESENTATION Open Access Projection imaging of ...
POSTER PRESENTATION Open Access
Projection imaging of myocardial perfusion:minimizing the subendocardial dark-rim artifactBehzad Sharif1,2*, Rohan Dharmakumar1,2, Troy Labounty1, Chrisandra Shufelt1, Louise Thomson1,Noel Bairey Merz1, Daniel S Berman1, Debiao Li1,2
From 15th Annual SCMR Scientific SessionsOrlando, FL, USA. 2-5 February 2012
SummaryWe demonstrate that projection imaging of first-passmyocardial perfusion is robust to a major cause of theso-called subendocardial dark-rim artifact (DRA);thereby proposing radial k-space sampling as the pre-ferred acquisition scheme for DRA-free perfusionimaging.
BackgroundCurrent methods for clinical myocardial perfusion (MP)imaging suffer from image artifacts, specifically the so-called subendocardial dark-rim artifact (DRA) [1-3].DRAs are especially limiting since they can reduce thesensitivity/specificity of detecting subendocardial MPdeficits; hence, eliminating such artifacts remains anactive area of research [1]. In this work, we demonstratethat projection imaging of MP is free of Gibbs ringing[2], a major cause of DRAs for conventional schemes.
MethodsIn Cartesian MP MR, Gibbs ringing along the phase-encode (PE) direction leads to DRAs due to an inherentproperty of the Fourier transform (FT) at sharp signalintensity transitions [2]. However, in projection imaging,the underlying data transform is the Radon transform[4], which does not exhibit the Gibbs ringing in thesame form as FT. This fact is demonstrated in Fig. 1using a numerical simulation. To investigate the validityof this observation in-vivo, healthy canines (N=2) andhealthy human volunteers (N=4; IRB approved) wereimaged on a clinical 3T scanner (Siemens Verio). Twofirst-pass MP scans (SR-prepared FLASH) were per-formed at rest (>10 minutes gap) using a single-shot
radial (customized) pulse sequence followed by a single-shot Cartesian (product) sequence (common parameters:FOV read = 270-300 mm; BW ≈ 800 Hz/pixel; flip angle= 12; TR = 2.4 ms; TI = 100 ms). Both scans were accel-erated using rate 2 self-calibrating parallel imaging with36-40 readouts. The customized radial sequence incor-porated gradient delay correction and a 4-fold interleav-ing scheme combined with KWIC processing [5].Although the readout resolution for the Cartesian scanwas higher than the base resolution for the radialscheme (≈1.8 mm vs. ≈2.2 mm), the overall resolutionof Cartesian (PE resolution≈2.6 mm) and radial scanswere matched to within 10%.
ResultsFig. 2 shows the reconstruction results for representativedog (a,b) and human (c,d) scans. Each pair of Cartesian/radial images correspond to the same phase of the con-trast uptake (late-LV/early-myocardial enhancement). Asis seen in the figure, Cartesian images (a,c) show DRAs(arrows pointing to hypo-intensities) in the subendocar-dial regions whereas the projection reconstructions (b,d)are free of dark rims (with slightly reduced CNR).
ConclusionsRecently, a major approach for eliminating the DRAshas been to improve the spatial resolution and therebyreducing Gibbs ringing [1,6]. In this work, we demon-strated that projection imaging is inherently robust toGibbs ringing. We conclude that an alternative strategy(besides increasing the resolution) is to employ projec-tion imaging (radial trajectories). The presented resultswere limited to rest scans, although we expect the sameproperties to hold for stress imaging. However, tomatch the high resolutions achieved in advanced Carte-sian schemes (e.g., [6]), rate 2 parallel imaging
1Biomedical Sciences, Biomedical Imaging Research Institute, Cedars-SinaiMedical Center, Los Angeles, CA, USAFull list of author information is available at the end of the article
Sharif et al. Journal of Cardiovascular Magnetic Resonance 2012, 14(Suppl 1):P275http://www.jcmr-online.com/content/14/S1/P275
© 2012 Sharif et al; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative CommonsAttribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction inany medium, provided the original work is properly cited.
acceleration is not sufficient and constrained highly-accelerated reconstruction will be needed.
FundingGrant sponsors: American Heart Association Postdoc-toral Fellowship Award 11POST7390063 (PI: B. Sharif);National Institutes of Health grants nos. NHLBIHL38698 (PI: D. Li) and NHLBI HL091989 (PI: R.Dharmakumar).
Author details1Biomedical Sciences, Biomedical Imaging Research Institute, Cedars-SinaiMedical Center, Los Angeles, CA, USA. 2Bioengineering, UCLA, Los Angeles,CA, USA.
Published: 1 February 2012
References1. Gerber , et al: JCMR. 2008, 10:18.2. Di Bella , et al: MRM. 2005, 54:1295.3. Ferreira , et al: JCMR. 2009, 11:17.
4. Kak , Slaney : IEEE press. 1988.5. Peters , et al: MRM. 2006, 55:1150.6. Plein , et al: MRM. 2007, 58:777.
doi:10.1186/1532-429X-14-S1-P275Cite this article as: Sharif et al.: Projection imaging of myocardialperfusion: minimizing the subendocardial dark-rim artifact. Journal ofCardiovascular Magnetic Resonance 2012 14(Suppl 1):P275.
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Figure 1 Numerical simulation (with realistic intensity values) demonstrating robustness of projection imaging to Gibbs ringing. (a) Cartesianimaging with 108 PEs (DRA is seen as highlighted); (b) projection imaging with 108 projections and filtered backprojection reconstruction (mildstreaking artifacts are present).
Figure 2 Representative in-vivo results for rest first-pass myocardial perfusion scans: (a,b) healthy canine model; (c,d) healthy human volunteer.Each pair of Cartesian/radial images corresponds to the same phase of the contrast uptake (late-LV or early-myocardial enhancement phase).The arrows in Panels (a) and (c) point to dark-rim artifacts (DRAs). However, DRAs are not seen in the projection-reconstruction (radial sampling)images in Panels (b) and (d).
Sharif et al. Journal of Cardiovascular Magnetic Resonance 2012, 14(Suppl 1):P275http://www.jcmr-online.com/content/14/S1/P275
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