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Perfusion Imaging Without Tunnel Vision^_*

Brigham and Women's Hospital, Boston, Massachusetts

Key Words: cardiac magnetic resonance • perfusion imaging • contrast-enhanced • fast imaging • coronary heart disease

The study raises the question of what spatial resolution will be adequate for an accurate detection of coronary artery disease. The glib answer would be that more is better, but higher spatial resolution means more limited coverage of the heart, and with the smaller voxel size, one has to accept a lower signal-to-noise ratio. Because the endocardial layer of the wall is most vulnerable to ischemia, it is necessary to have sufficient spatial resolution to resolve a transmural perfusion gradient (2); this has been an advantage of CMR versus nuclear imaging. But how far do we need to carry this, or is the spatial resolution used in a recent, large, multicenter study sufficient (3)? The answer remains to be determined. Manka et al. (1) present some results from an analysis of their studies in which the spatial resolution was reduced by post-processing, but arguably, they do not provide a conclusive answer yet. Rather, a larger, preferably multicenter study is needed to test performance at different spatial resolution settings in the clinical setting.

What are the limitations of the technical developments that led to the study by Manka et al. (1)? For one, any sort of acceleration of the image acquisition generally extracts a penalty in terms of signal-to-noise ratio. The investigators tested their new method on a magnetic resonance imaging scanner operating at 3-T, a field strength that is still rarely used for routine cardiac imaging in the clinical setting, but the higher field strength certainly compensated in part for any decrease in signal-to-noise ratio due to acceleration of the image acquisition (4). It also remains unknown how the techniques for accelerated imaging used by Manka et al. (1) compare with other noteworthy alternatives for more rapid CMR perfusion imaging. Several are under active development at CMR research centers, with one, highly constrained back projection (5), achieving the surprising feat of high acceleration and improved contrast-to-noise ratios. Remarkable developments in this area also include compressive sensing, a novel concept that has overturned the sampling requirement embodied in the 50-year-old Shannon-Nyquist theorem, which implied for magnetic resonance that images need to be acquired over a regularly spaced grid of points with a minimal distance between the sampling points to avoid aliasing (6). It has turned out that sparse pseudo-random subsets of spatial encodings can be sufficient for the reconstruction of an image, assuming that one has some a priori knowledge of how the image is best compressed. There may therefore be more than one good cure to tunnel vision in CMR perfusion imaging, and the next few years promise important advances in this area. How the benefits of these technical advances will be apportioned to optimize different aspects important to MPI remains to be seen, but Manka et al. (1) are among the very first to show that these advances are not just an ivory-tower concept, but robust enough for the CMR clinic and with substantial benefits for fast perfusion imaging.

	Footnotes

 
^_* Editorials published in JACC: Cardiovascular Imaging reflect the views of the authors and do not necessarily represent the views of JACC: Cardiovascular Imaging or the American College of Cardiology.

^_* Reprint requests and correspondence: Dr. Michael Jerosch-Herold, Brigham and Women's Hospital, Department of Radiology, 75 Francis Street, Boston, Massachusetts 02115 (Email: mjerosch-herold{at}bics.bwh.harvard.edu).

	REFERENCES

Top REFERENCES

 

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2. Bache RJ, Schwartz JS. Effect of perfusion pressure distal to a coronary stenosis on transmural myocardial blood flow Circulation 1982;65:928-935.[Abstract/Free Full Text]
3. Schwitter J, Wacker CM, van Rossum AC, et al. MR-IMPACT: comparison of perfusion-cardiac magnetic resonance with single-photon emission computed tomography for the detection of coronary artery disease in a multicentre, multivendor, randomized trial Eur Heart J 2008;29:480-489.[Abstract/Free Full Text]
4. Cheng AS, Pegg TJ, Karamitsos TD, et al. Cardiovascular magnetic resonance perfusion imaging at 3-tesla for the detection of coronary artery disease: a comparison with 1.5-tesla J Am Coll Cardiol 2007;49:2440-2449.[Abstract/Free Full Text]
5. Ge L, Kino A, Griswold M, Mistretta C, Carr JC, Li D. Myocardial perfusion MRI with sliding-window conjugate-gradient HYPR Magn Reson Med 2009;62:835-839.[CrossRef][Web of Science][Medline]
6. Lustig M, Donoho D, Pauly JM. Sparse MRI: the application of compressed sensing for rapid MR imaging Magn Reson Med 2007;58:1182-1195.[CrossRef][Web of Science][Medline]

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