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Wang Y, Kim SE, DiBella EVR, Parker DL. Flow measurement in MRI using arterial spin labeling with cumulative readout pulses--theory and validation. Med Phys 2011; 37:5801-10. [PMID: 21158292 DOI: 10.1118/1.3501881] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE This article systematically examines arterial spin labeling (ASL) as a flow quantification technique through theoretical simulation, in vitro, and in vivo experiment. The authors present a novel imaging pulse sequence design consisting of a single ASL magnetization preparation followed by Look-Locker-like image readouts. Bloch-equation-based modeling has been developed and validated using a hemodialyzer as a tissue-mimicking flow phantom. METHODS After the single in-plane slice-selective double inversion magnetization preparation, multiple TFL readouts are acquired with linear k-space ordering, causing a signal variation that depends on through-slice flow velocity. Computer simulations were performed to assess the behavior of the flow-dependent ASL signal as a function of varying imaging parameters. The signal was optimized by choosing imaging parameters that maximize the simulated flow-sensitive signal. Furthermore, a hemodialyzer which mimics blood flow in human tissues was tested with a wide range of flow rates. An exponential curve fitting of the flow-sensitive dynamics to the model derived from Bloch equations provides a method to estimate through-slice velocity for varying flow rates on the hemodialyzer and in vivo human brain. RESULTS The flow dependency of the ASL signal and the sensitivity of the ASL signal to imaging parameters were demonstrated. Experimental results from a hemodialyzer when fitted with a Bloch-equation-based model provide flow measurements that are consistent with ground truth velocities. Human brain velocity mapping was obtained as well. CONCLUSIONS The results provide evidence that the proposed pulse sequence design is an effective technique to measure total fluid flow through image voxels. The unique combination of the two main features, multiple-image readout after a single ASL preparation and linear acquisition ordering in the phase encoding direction in TFL imaging, make this technique an appealing flow imaging method to quantify through-plane flow in a time-efficient manner.
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Affiliation(s)
- Yi Wang
- Department of Bioengineering, University of Utah, 729 Arapeen Drive, Salt Lake City, Utah 84108, USA
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Patel AR, Epstein FH, Kramer CM. Evaluation of the microcirculation: advances in cardiac magnetic resonance perfusion imaging. J Nucl Cardiol 2009; 15:698-708. [PMID: 18761273 DOI: 10.1016/j.nuclcard.2008.07.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- Amit R Patel
- Department of Medicine, University of Virginia Health System, Charlottesville, VA 22908, USA
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Warmuth C, Nagel S, Hegemann O, Wlodarczyk W, Lüdemann L. Accuracy of blood flow values determined by arterial spin labeling: A validation study in isolated porcine kidneys. J Magn Reson Imaging 2007; 26:353-8. [PMID: 17654732 DOI: 10.1002/jmri.21011] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
PURPOSE To validate the accuracy of quantitative blood flow values determined using pulsed arterial spin labeling (ASL) in the preserved and reperfused porcine kidney. MATERIALS AND METHODS Ex vivo porcine kidneys were perfused with whole blood under physiological conditions, in particular including pulsatile flow. Total flow through the kidney was determined using an ultrasound flowmeter. ASL measurements at two different inversion times and four different flow rates in the range of 70-210 mL/100 mL*minute were performed. Absolute values of blood flow and arterial transit times were determined in the kidney cortex. RESULTS The quantitative values were in good agreement with the reference values obtained after calibration of the total flow. The greatest difference observed was 13%. CONCLUSION Isolated organ hemoperfusion allows validating perfusion imaging techniques. The experimental setup enables long-term radiotherapeutic or toxicological studies using noninvasive ASL to monitor blood flow quantitatively.
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Affiliation(s)
- Carsten Warmuth
- Department of Radiology, Charité-Universitary Medicine Berlin, Campus Charité-Mitte (CCM), Berlin, Germany
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Stehning C, Boernert P, Nehrke K. Advances in Coronary MRA from Vessel Wall to Whole Heart Imaging. Magn Reson Med Sci 2007; 6:157-70. [PMID: 18037796 DOI: 10.2463/mrms.6.157] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
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Petersen ET, Zimine I, Ho YCL, Golay X. Non-invasive measurement of perfusion: a critical review of arterial spin labelling techniques. Br J Radiol 2006; 79:688-701. [PMID: 16861326 DOI: 10.1259/bjr/67705974] [Citation(s) in RCA: 244] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The non-invasive nature of arterial spin labelling (ASL) has opened a unique window into human brain function and perfusion physiology. High spatial and temporal resolution makes the technique very appealing not only for the diagnosis of vascular diseases, but also in basic neuroscience where the aim is to develop a more comprehensive picture of the physiological events accompanying neuronal activation. However, low signal-to-noise ratio and the complexity of flow quantification make ASL one of the more demanding disciplines within MRI. In this review, the theoretical background and main implementations of ASL are revisited. In particular, the perfusion quantification methods, including the problems and pitfalls involved, are thoroughly discussed in this article. Finally, a brief summary of applications is provided.
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Affiliation(s)
- E T Petersen
- Department of Neuroradiology, National Neuroscience Institute, Singapore
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6
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Abstract
Arterial spin labeling (ASL) in combination with NMR imaging is an in vivo technique that quantifies tissue perfusion in absolute values (ml blood x min(-1) x g tissue(-1)) with high temporal (1-10 s) and spatial (0.1-3 mm) resolution. It uses the arterial water spins as endogenous freely diffusible markers of perfusion and, hence, is a totally noninvasive method. The technique has been successfully applied to quantify baseline perfusion in many organs, including the heart, in humans and animals, and results were validated by comparison with gold standards, PET and microspheres, respectively. Because of the high sampling rate of perfusion with ASL and the possibility that measurements could be obtained without harm over indefinite periods of time, the technique has the potential for use in functional investigations of microcirculation regulation and resistance artery control in vivo. We describe examples of the use of ASL to this end. With use of specific technological developments, ASL determination of perfusion can be coupled with simultaneous acquisitions of (1)H and (31)P NMR spectroscopy data. These protocols offer new possibilities whereby the microcirculatory control of cell oxygenation and high-energy phosphate metabolism can be explored.
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Klem I, Rehwald WG, Heitner JF, Wagner A, Albert T, Parker MA, Chen EL, Kim RJ, Judd RM. Noninvasive assessment of blood flow based on magnetic resonance global coherent free precession. Circulation 2005; 111:1033-9. [PMID: 15723978 DOI: 10.1161/01.cir.0000156332.56894.22] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Magnetic resonance global coherent free precession (GCFP) is a new technique that produces cine projection angiograms directly analogous to those of x-ray angiography noninvasively and without a contrast agent. In this study, we compared GCFP blood flow with "gold standards" to determine the accuracy of noninvasive GCFP blood flow measurements. METHODS AND RESULTS The relationship between GCFP blood flow and true blood flow defined by invasive ultrasonic flow probe and by phase contrast velocity encoded MRI (VENC) was studied in anesthetized dogs (n=6). Blood flow was controlled by use of a hydraulic occluder around the left iliac artery. GCFP images were acquired by selectively exciting the abdominal aorta and visualizing temporal blood flow into the iliac arteries. GCFP flow was similar to ultrasonic blood flow at baseline (131.3+/-44.8 versus 114.8+/-34.2 mL/min), during occlusion (10.8+/-5.1 versus 6.5+/-7.2 mL/min), during reactive hyperemia (191.4+/-100.7 versus 260.3+/-138.7 mL/min), during the new resting state (135.5+/-52.4 versus 117.8+/-24.1 mL/min), and during partial occlusion (61.4+/-36.4 versus 49.3+/-13.1 mL/min, P=NS for all). Results comparing GCFP flow with VENC were similar. Statistical analysis revealed that GCFP flow was related to mean blood flow assessed by the flow probe (P<0.0001) and by VENC (P<0.0001). In the control right iliac artery, conversely, GCFP measurements were unaffected throughout all left iliac interventions (P=NS). CONCLUSIONS GCFP blood flow is linearly related to true blood flow for a straight, cylindrical blood vessel without branches. Although more complex geometries imply a qualitative rather than a quantitative relationship, the data nevertheless suggest that GCFP may serve as the basis for a new form of noninvasive stress testing.
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Affiliation(s)
- Igor Klem
- Duke Cardiovascular Magnetic Resonance Center, Durham, NC 27710, USA
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8
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Vignaux O. [Cardiac magnetic resonance imaging (MRI)]. Presse Med 2004; 33:891-5. [PMID: 15387389 DOI: 10.1016/s0755-4982(04)98779-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
TECHNOLOGICAL PROGRESS: Although cardiac magnetic resonance imaging (MRI) is now recognised as the imaging method of choice for the morphological study of the heart, recent technological progress have widened its indications to functional analysis of the heart rate, perfusion and contractility. FUNCTIONAL ASSESSMENT: The possibility of conducting pharmacological stress tests enhances the functional exploration of cardiac perfusion and contractility. The rapid sequences in apnea, tissue marking and injection of contrast products are all elements that help to refine the study of the locoregional consequences of an ischemia: does the myocardial tissue contract normally? Is it sufficiently perfused? Is it still viable? THE BENEFITS OF A NON-INVASIVE TECHNIQUE: The MRI offers clinicians a non-invasive and non-radiating imaging technique that is the perfect supplement to echocardiography. A reliable angio-coronary LRI technique would, for the first time, permit exploration of the coronary vascularisation, tissue perfusion and resulting contractility.
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Affiliation(s)
- Olivier Vignaux
- Service de radiologie A, Hôpital Cochin 27, rue du Fbg St Jacques, 75014 Paris.
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Abstract
Arterial spin labeling is a magnetic resonance method for the measurement of cerebral blood flow. In its simplest form, the perfusion contrast in the images gathered by this technique comes from the subtraction of two successively acquired images: one with, and one without, proximal labeling of arterial water spins after a small delay time. Over the last decade, the method has moved from the experimental laboratory to the clinical environment. Furthermore, numerous improvements, ranging from new pulse sequence implementations to extensive theoretical studies, have broadened its reach and extended its potential applications. In this review, the multiple facets of this powerful yet difficult technique are discussed. Different implementations are compared, the theoretical background is summarized, and potential applications of various implementations in research as well as in the daily clinical routine are proposed. Finally, a summary of the new developments and emerging techniques in this field is provided.
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Affiliation(s)
- Xavier Golay
- Department of Neuroradiology, National Neuroscience Institute, Singapore.
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Rehwald WG, Chen EL, Kim RJ, Judd RM. Noninvasive cineangiography by magnetic resonance global coherent free precession. Nat Med 2004; 10:545-9. [PMID: 15064758 DOI: 10.1038/nm1027] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2003] [Accepted: 02/20/2004] [Indexed: 11/09/2022]
Abstract
Cardiovascular disease is primarily diagnosed using invasive X-ray cineangiography. Here we introduce a new concept in magnetic resonance imaging (MRI) that, for the first time, produces similar images noninvasively and without a contrast agent. Protons in moving blood are 'tagged' every few milliseconds as they travel through an arbitrary region in space. Simultaneous with ongoing tagging of new blood, previously tagged blood is maintained in a state of global coherent free precession (GCFP), which allows acquisition of consecutive movie frames as the heart pushes blood through the vascular bed. Body tissue surrounding the moving blood is never excited and therefore remains invisible. In 18 subjects, pulsating blood could be seen flowing through three-dimensional (3D) space for distances of up to 16 cm outside the stationary excitation region. These data underscore that our approach noninvasively characterizes both anatomy and blood flow in a manner directly analogous to invasive procedures.
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Affiliation(s)
- Wolfgang G Rehwald
- Duke Cardiovascular Magnetic Resonance Center, Duke University Medical Center, PO Box 3934, Durham, North Carolina 27710, USA
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Wacker CM, Fidler F, Dueren C, Hirn S, Jakob PM, Ertl G, Haase A, Bauer WR. Quantitative assessment of myocardial perfusion with a spin-labeling technique: preliminary results in patients with coronary artery disease. J Magn Reson Imaging 2004; 18:555-60. [PMID: 14579398 DOI: 10.1002/jmri.10386] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE To determine perfusion and coronary reserve in human myocardium without contrast agent using a spin labeling technique. MATERIALS AND METHODS Assessment of myocardial perfusion is based on T1 measurements after global and slice-selective spin preparation. This magnetic resonance imaging (MRI) technique was applied to 12 healthy volunteers and 16 patients with suspected coronary artery disease under resting conditions and adenosine-induced vasodilatation. RESULTS In volunteers, quantitative perfusion was calculated as 2.4 +/- 1.2 mL/g/minute (rest) and 3.9 +/- 1.3 mL/g/minute (adenosine), respectively. Perfusion reserve was 2.1 +/- 0.6. In patients, when comparing perfusion reserve in the anterior and posterior myocardium, reduced values according to a stenotic supplying vessel could be seen in seven of 11 patients who underwent stress testing. In these patients, the relative difference of coronary reserve was 44% +/- 18%. Two patients without stenosis of coronary arteries showed no differences in coronary reserve (with a relative change of 2 +/- 2%). CONCLUSION In patients with single-vessel coronary artery disease, differences in coronary reserve were clearly detectable when comparing anterior and posterior myocardium. The spin labeling method is noninvasive and easily repeatable, and it could therefore become an important tool to study changes in myocardial perfusion.
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12
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Forder JR, Pohost GM. Cardiovascular nuclear magnetic resonance: basic and clinical applications. J Clin Invest 2003. [DOI: 10.1172/jci200318868] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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Forder JR, Pohost GM. Cardiovascular nuclear magnetic resonance: basic and clinical applications. J Clin Invest 2003; 111:1630-9. [PMID: 12782663 PMCID: PMC156119 DOI: 10.1172/jci18868] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Affiliation(s)
- John R Forder
- Division of Cardiovascular Medicine, Keck School of Medicine, The University of Southern California, Los Angeles, California 90033, USA
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Stuber M, Börnert P, Spuentrup E, Botnar RM, Manning WJ. Selective three-dimensional visualization of the coronary arterial lumen using arterial spin tagging. Magn Reson Med 2002; 47:322-9. [PMID: 11810676 DOI: 10.1002/mrm.10042] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Conventional coronary magnetic resonance angiography (MRA) techniques display the coronary blood-pool along with the surrounding structures, including the myocardium, the ventricular and atrial blood-pool, and the great vessels. This representation of the coronary lumen is not directly analogous to the information provided by x-ray coronary angiography, in which the coronary lumen displayed by iodinated contrast agent is seen. Analogous "luminographic" data may be obtained using MR arterial spin tagging (projection coronary MRA) techniques. Such an approach was implemented using a 2D selective "pencil" excitation for aortic spin tagging in concert with a 3D interleaved segmented spiral imaging sequence with free-breathing, and real-time navigator technology. This technique allows for selective 3D visualization of the coronary lumen blood-pool, while signal from the surrounding structures is suppressed.
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Affiliation(s)
- Matthias Stuber
- Cardiovascular Division, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA.
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15
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Raynaud JS, Duteil S, Vaughan JT, Hennel F, Wary C, Leroy-Willig A, Carlier PG. Determination of skeletal muscle perfusion using arterial spin labeling NMRI: validation by comparison with venous occlusion plethysmography. Magn Reson Med 2001; 46:305-11. [PMID: 11477634 DOI: 10.1002/mrm.1192] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
T(1)-based determination of perfusion was performed with the high temporal and spatial resolution that monitoring of exercise physiology requires. As no data were available on the validation of this approach in human muscles, T(1)-based NMRI of perfusion was compared to standard strain-gauge venous occlusion plethysmography performed simultaneously within a 4 T magnet. Two different situations were investigated in 21 healthy young volunteers: 1) a 5-min ischemia of the leg, or 2) a 2-3 min ischemic exercise consisting of a plantar flexion on an amagnetic ergometer. Leg perfusion was monitored over 5-15 min of the recovery phase, after the air-cuff arterial occlusion had been released. The interesting features of the sequence were the use of a saturation-recovery module for the introduction of a T(1) modulation and of single-shot spin echo for imaging. Spatial resolution was 1.7 x 2.0 mm and temporal resolution was 2 s. For data analysis, ROIs were traced on different muscles and perfusion was calculated from the differences in muscle signal intensity in successive images. To allow comparison with the global measurement of perfusion by plethysmography, the T(1)-based NMR measurements in exercising muscles were rescaled to the leg cross-section. The perfusion measurements obtained by plethysmography and NMRI were in close agreement with a correlation coefficient between 0.87 and 0.92. This indicates that pulsed arterial techniques provide determination of muscle perfusion not only with superior spatial and temporal resolution but also with exactitude.
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Affiliation(s)
- J S Raynaud
- NMR Unit (AFM, CEA and INSERM), Institute of Myology, Pitié-Salpêtrièere University Hospital, Paris, France
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Bauer WR, Hiller KH, Galuppo P, Neubauer S, Köpke J, Haase A, Waller C, Ertl G. Fast high-resolution magnetic resonance imaging demonstrates fractality of myocardial perfusion in microscopic dimensions. Circ Res 2001; 88:340-6. [PMID: 11179203 DOI: 10.1161/01.res.88.3.340] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The fractal nature of heterogeneity of myocardial blood flow and its implications for the healthy and diseased heart is not yet understood. The main hindrance for investigation of blood flow heterogeneity and its role in physiology and pathophysiology is that conventional methods for determination of myocardial perfusion have severe limitations concerning temporal and spatial resolution and invasiveness. In isolated rat hearts, we developed a nuclear magnetic resonance technique that does not depend on contrast agents and in which the apparent longitudinal relaxation time is made perfusion sensitive by selective preparation of the imaging slice. This perfusion-sensitive relaxation time is determined within 40 seconds as a map with a high spatial in-plane resolution of 140x140 microm(2) and a thickness of 1.5 mm. Perfusion imaging was validated with the established microsphere technique. Additionally, the congruence between perfusion-sensitive T:(1) maps and first-pass perfusion imaging was demonstrated. As an application of high-resolution perfusion imaging, fractal analysis of the spatial distribution of perfusion was performed. We were able to demonstrate that the fractality of this distribution exists even in microscopic dimensions. Vasodilation by nitroglycerin modulated the fractal pattern of perfusion, and the decrease of the fractal dimension indicated a shift toward homogeneity. This implies that parameters of the fractal distribution depend on the microvascular tone rather than on anatomic preformations; ie, fractality is a functional characteristic of perfusion.
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Affiliation(s)
- W R Bauer
- Medizinische Universitätsklinik, Universität Würzburg, Germany.
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Scollan DF, Holmes A, Zhang J, Winslow RL. Reconstruction of cardiac ventricular geometry and fiber orientation using magnetic resonance imaging. Ann Biomed Eng 2000; 28:934-44. [PMID: 11144678 PMCID: PMC1473035 DOI: 10.1114/1.1312188] [Citation(s) in RCA: 120] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
An imaging method for the rapid reconstruction of fiber orientation throughout the cardiac ventricles is described. In this method, gradient-recalled acquisition in the steady-state (GRASS) imaging is used to measure ventricular geometry in formaldehyde-fixed hearts at high spatial resolution. Diffusion-tensor magnetic resonance imaging (DTMRI) is then used to estimate fiber orientation as the principle eigenvector of the diffusion tensor measured at each image voxel in these same hearts. DTMRI-based estimates of fiber orientation in formaldehyde-fixed tissue are shown to agree closely with those measured using histological techniques, and evidence is presented suggesting that diffusion tensor tertiary eigenvectors may specify the orientation of ventricular laminar sheets. Using a semiautomated software tool called HEARTWORKS, a set of smooth contours approximating the epicardial and endocardial boundaries in each GRASS short-axis section are estimated. These contours are then interconnected to form a volumetric model of the cardiac ventricles. DTMRI-based estimates of fiber orientation are interpolated into these volumetric models, yielding reconstructions of cardiac ventricular fiber orientation based on at least an order of magnitude more sampling points than can be obtained using manual reconstruction methods.
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Affiliation(s)
| | | | | | - R. L. Winslow
- Address correspondence to R. L. Winslow, Rm. 411 Traylor Research Bldg., The Johns Hopkins University School of Medicine, 720 Rutland Ave., Baltimore, MD 21205. Electronic mail:
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Waller C, Kahler E, Hiller KH, Hu K, Nahrendorf M, Voll S, Haase A, Ertl G, Bauer WR. Myocardial perfusion and intracapillary blood volume in rats at rest and with coronary dilatation: MR imaging in vivo with use of a spin-labeling technique. Radiology 2000; 215:189-97. [PMID: 10751486 DOI: 10.1148/radiology.215.1.r00ap07189] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
PURPOSE To validate a magnetic resonance (MR) imaging technique that is not first pass and that reveals perfusion and regional blood volume (RBV) in the intact rat. MATERIALS AND METHODS Measurement of perfusion was based on the perfusion-sensitive T1 relaxation after magnetic spin labeling of water protons. RBV was determined from steady-state measurements of T1 before and after administration of an intravascular contrast agent. The colored microsphere technique was used as a reference method for perfusion measurement. RBV and perfusion maps were obtained with the rats at rest and during administration of 3 mg of adenosine phosphate per kilogram of body weight per minute. RESULTS At MR imaging, perfusion during resting conditions was 3.5 mL/g/min +/- 0.1 (SEM), and RBV was 11.6% +/- 0.6 (SEM). Adenosine phosphate significantly increased perfusion to 4.5 mL/g/min +/- 0.3 (SEM) and decreased mean arterial pressure from 120 mm Hg to 65 mm Hg, which implies a reduction of coronary resistance to 40% of baseline. RBV increased consistently to 23.8% +/- 0.6 (SEM). CONCLUSION The study results show that quantitative mapping of perfusion and RBV may be performed noninvasively by means of MR imaging in the intact animal. The presented method allows determination of vasodilative and perfusion reserve, which reflects the in vivo regulation of coronary microcirculation for a given stimulus.
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Affiliation(s)
- C Waller
- Medical Institute, University of Würzburg, Josef-Schneider-Str. 2, 97080 Würzburg, Germany. wallerphysik.uni-wuerzburg.de
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Reeder SB, Holmes AA, McVeigh ER, Forder JR. Simultaneous noninvasive determination of regional myocardial perfusion and oxygen content in rabbits: toward direct measurement of myocardial oxygen consumption at MR imaging. Radiology 1999; 212:739-47. [PMID: 10478241 PMCID: PMC2041908 DOI: 10.1148/radiology.212.3.r99se27739] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
PURPOSE To determine whether myocardial arterial perfusion and oxygen concentration can be quantified simultaneously from the same images by using spin labeling and the blood oxygenation level-dependent (BOLD) effect with fast spin-echo (SE) imaging. MATERIALS AND METHODS A T2-weighted fast SE pulse sequence was written to image isolated, arrested, blood-perfused rabbit hearts (n = 6) at 4.7 T. Perfusion images with intensity in units of milliliters per minute per gram that covered the entire left ventricle with 0.39 x 0.39 x 3.00-mm resolution were obtained in less than 15 minutes with a 32-fold reduction in imaging time from that of a previous study. Estimates of oxygen concentration were made from the same images acquired for calculation of perfusion images. RESULTS Estimates of regional myocardial oxygen content could be made from the perfusion images; this demonstrated the feasibility of three-dimensional calculation of regional oxygen consumption, which requires concomitant measurement of both oxygen content and flow. Fast SE imaging was shown to be as sensitive to hemoglobin desaturation as standard SE imaging. Perfusion abnormalities and oxygen deficits were easily identified and verified qualitatively with gadopentetate dimeglumine on both perfusion and BOLD images obtained after coronary arterial ligation. CONCLUSION T2-weighted fast SE imaging combined with perfusion-sensitive spin labeling can be used to measure myocardial arterial perfusion and oxygen concentration. This provides the groundwork for calculation of regional myocardial oxygen consumption.
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Affiliation(s)
- S B Reeder
- Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, Md., USA
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Poncelet BP, Koelling TM, Schmidt CJ, Kwong KK, Reese TG, Ledden P, Kantor HL, Brady TJ, Weisskoff RM. Measurement of human myocardial perfusion by double-gated flow alternating inversion recovery EPI. Magn Reson Med 1999; 41:510-9. [PMID: 10204874 DOI: 10.1002/(sici)1522-2594(199903)41:3<510::aid-mrm13>3.0.co;2-g] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
This paper presents a flow-sensitive alternating inversion recovery (FAIR) method for measuring human myocardial perfusion at 1.5 T. Slice-selective/non-selective IR images were collected using a double-gated IR echoplanar imaging sequence. Myocardial perfusion was calculated after T1 fitting and extrapolation of the mean signal difference SI(Sel - SI(NSel). The accuracy of the method was tested in a porcine model using graded intravenous adenosine dose challenge. Comparison with radiolabeled microsphere measurements showed a good correlation (r = 0.84; mean error = 20%, n = 6) over the range of flows tested (0.9-7 ml/g/min). Applied in humans, this method allowed for the measurement of resting myocardial flow (1.04+/-0.37 ml/g/min, n = 11). The noise in our human measurements (SE(flow) = 0.2 ml/g/min) appears to come primarily from residual respiratory motion. Although the current signal-to-noise ratio limits our ability to measure small fluctuations in resting flow accurately, the results indicate that this noninvasive method has great promise for the quantitative assessment of myocardial flow reserve in humans.
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Affiliation(s)
- B P Poncelet
- Massachusetts General Hospital NMR Center, Charlestown, Massachusetts 02129, USA.
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Belle V, Kahler E, Waller C, Rommel E, Voll S, Hiller KH, Bauer WR, Haase A. In vivo quantitative mapping of cardiac perfusion in rats using a noninvasive MR spin-labeling method. J Magn Reson Imaging 1998; 8:1240-5. [PMID: 9848735 DOI: 10.1002/jmri.1880080610] [Citation(s) in RCA: 99] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Measurement of myocardial perfusion is important for the functional assessment of heart in vivo. Our approach is based on the modification of the longitudinal relaxation time T1 induced by magnetic spin labeling of endogenous water protons. Labeling is performed by selectively inverting the magnetization within the detection slice, and longitudinal relaxation is measured using a fast gradient echo MRI technique. As a result of blood flow, nonexcited spins enter the detection slice, which leads to an acceleration of the relaxation rate. Incorporating this phenomenon in a mathematical model that describes tissue as two compartments yields a simple expression that allows the quantification of perfusion from a slice-selective and a global inversion recovery experiment. This model takes into account the difference between T1 in blood and T1 in tissue. Our purpose was to evaluate the feasibility and reproducibility of this technique to map quantitatively myocardial perfusion in vivo in rats. Quantitative maps of myocardial blood flow were obtained from nine rats, and the reproducibility of the technique was evaluated by repeating the whole perfusion experiment four times. Evaluation of regions of interest within the myocardium yielded a mean perfusion value of 3.6 +/- .5 ml x min(-1) x g(-1) over all animals, which is in good agreement with previously reported literature values.
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Affiliation(s)
- V Belle
- Physikalisches Institut, Universität Würzburg, Germany
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23
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Abstract
Noninvasive qualitative/quantitative assessment of myocardial perfusion is considered to be fundamental in the management of known and suspected coronary artery disease patients, as shown by the widespread utilization of thallium-201- and technetium-99m-labeled agents in myocardial single-photon emission computed tomography (SPECT) scintigraphy for diagnostic as well as prognostic purposes. Recently, the availability of subsecond ultrafast magnetic resonance imaging (MRI) sequences (FLASH, TurboFLASH, EPI) has provided new avenues for assessing myocardial perfusion by MRI in conjunction with contrast-agent bolus administration (contrast-enhanced first-pass MRI). MRI contrast agents can be classified into relaxation agents (T1 "positive") and susceptibility agents (T2 star [T2*] "negative"). All the commercially available MRI contrast agents used in clinical practice are relaxation agents employing the T1 shortening effect of metal ions like gadolinium (paramagnetism), thus producing a tissue signal-intensity increase on T1-weighted images (positive enhancement). On the other hand, T2* agents induce mainly susceptibility effects, i.e., rapid dephasing of spins with resultant signal loss on T2*-sensitive sequences (negative enhancement). Unfortunately, both relaxation and susceptibility agents are, by definition, "extracellular" contrast media, as they rapidly diffuse into the interstitial space, thus hampering the simple application of indicator-dilution kinetics for myocardial perfusion assessment. Blood pool agents are therefore needed to obtain predictable relations between the concentration of contrast medium in the myocardium and the change in signal intensity. In addition, newer MRI techniques for tissue perfusion quantitation have been recently reported, based on blood-sensitive sequences, thus without intravenous contrast administration.
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Affiliation(s)
- R Passariello
- Department of Radiology, University of Rome, La Sapienza, Italy
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Harris PA, Lorenz CH, Holburn GE, Overholser KA. Regional measurement of the Gd-DTPA tissue partition coefficient in canine myocardium. Magn Reson Med 1997; 38:541-5. [PMID: 9324319 DOI: 10.1002/mrm.1910380406] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Quantifiable MRI perfusion studies using the contrast agent Gd-DTPA require measurement or estimation of the tissue partition coefficient (lambda) for tracer kinetic modeling. Radiotracer techniques were used to obtain regional lambda measurements from the left ventricles of five dogs. Measurements were analyzed to determine whether spatial heterogeneity was a major component of lambda variability. No systematic variations were identified in terms of radial position, short-axis slice location, or wall position. The high lambda variability seen in this study and in cited data of others may be due in part to tissue heterogeneity in interstitial volume, plasma volume, and perfusate hematocrit.
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Affiliation(s)
- P A Harris
- General Clinical Research Center, Medical College of Virginia, Richmond 23298, USA
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Reeder SB, Atalar E, Bolster BD, McVeigh ER. Quantification and reduction of ghosting artifacts in interleaved echo-planar imaging. Magn Reson Med 1997; 38:429-39. [PMID: 9339445 PMCID: PMC2396297 DOI: 10.1002/mrm.1910380312] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
A mathematical analysis of ghosting artifacts often seen in interleaved echo-planar images (EPI) is presented. These artifacts result from phase and amplitude discontinuities between lines of k-space in the phase-encoding direction, and timing misregistrations from system filter delays. Phase offsets and time delays are often measured using "reference" scans, to reduce ghosting through postprocessing. From the expressions describing ghosting artifacts, criteria were established for reducing ghosting to acceptable levels. Subsequently, the signal-to-noise ratio (SNR) requirements for estimation of time delays and phase offsets, determined from reference scans, was evaluated to establish the effect of estimation error on artifact reduction for interleaved EPI. Artifacts resulting from these effects can be reduced to very low levels when appropriate reference scan estimation is used. This has important implications for functional MRI (fMRI) and applications involving small changes in signal intensity.
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Affiliation(s)
- S B Reeder
- Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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26
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Crnac J, Schmidt MC, Theissen P, Sechtem U. Assessment of myocardial perfusion by magnetic resonance imaging. Herz 1997; 22:16-28. [PMID: 9088937 DOI: 10.1007/bf03044567] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Magnetic resonance imaging (MRI) has proven useful for anatomic and functional evaluation of the heart. However, until recently assessment of myocardial perfusion has not been possible by MRI. Using newly developed ultrafast imaging sequences, images can be acquired rapidly with a high temporal resolution, which is a prerequisite for imaging the initial passage of a bolus of MR-contrast medium through the myocardium. Only gadolinium chelates, which rapidly diffuse out of vascular space, are currently approved for clinical use. The first pass of a bolus of one of these agents through hypoperfused myocardium distal to a coronary artery stenosis enhances this area less as compared to normally perfused areas. This different myocardial enhancement is often visible when looking at the series of MR images. However, intensity differences are rapidly decreasing as MR-contrast media are diluted in the systemio circulation after the first pass and diffuse to the interstitium. Therefore, only the first pass is of interest for MR-perfusion imaging. Additional and often more precise information can be derived by measuring parameters of the signal intensity time curve such as mean transit time, maximum signal intensity increase, upslope, downslope, and delay before reaching maximum signal intensity. Temporal resolution is the crucial factor in MR-perfusion imaging because it takes only 20 to 60 seconds for the contrast medium to pass through the myocardium. Therefore, this dynamic process must be imaged with a high temporal resolution. Moreover, image acquisition must be fast enough to minimize motion artefacts and to maximize the spatial coverage of the ventricle. Ultrafast gradient echo techniques and echo planar imaging are in principle capable to fulfill these demands. While ultrafast gradient echo sequences enable one to acquire a maximum of 2 slices per heartbeat, echo planar sequences need only 30 to 50 msec to completely acquire one image and are thus able to image the entire ventricle within one heartbeat. However, they are also more susceptible to image artefacts. As gradients capable of producing high quality echo planar images are not widely available, ultrafast gradient echo techniques are commonly used for MR-perfusion imaging. A good correlation between quantitative estimates of myocardial perfusion by MRI after injection of an intravascular contrast agent and microsphere measurements has been shown in animal experiments but quantitative MR perfusion measurements have not yet been performed in humans. Clinical studies have until now focused on visual and parametric analysis of signal intensity time curves. From these studies, sensitivities and specifities in the range of 60 to 90% as compared to x-ray coronary angiography and scintigraphy were reported despite the fact that only parts of the left ventricular myocardium could be assessed. However, a generally accepted method of acquiring and analysing MR perfusion images does not yet exist. Therefore, future improvements of hardware and pulse-sequences as well as the development of new blood pool contrast agents are necessary before MR-perfusion imaging will become a widely accepted and clinically useful diagnostic procedure.
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Affiliation(s)
- J Crnac
- Klinik III für Innere Medizin, Universität zu Köln
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