MR imaging of motion with spatial modulation of magnetization.

Axel, Leon; Dougherty, Lawrence

doi:10.1148/radiology.171.3.2717762

Cited by 1,072 publications

(691 citation statements)

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“…We used the smoothness constraint [2] where u i and x i are the ith components of the spatial coordinate displacement field and the spatial coordinate position vector, respectively. This smoothness constraint minimizes the spatial variation of the displacement field.…”

Section: Spatial Coordinate Displacement Fitmentioning

confidence: 99%

“…Therefore, larger attenuation values correspond to greater smoothing. Note that although the smoothness constraint in Equation [2] is isotropic, the effective smoothing in the reconstruction is slightly different in each direction because of variations in the tag structure around each displaced tag point.…”

Section: Spatial Resolution Of the Dmf Strain Reconstructionmentioning

confidence: 99%

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Model‐free reconstruction of three‐dimensional myocardial strain from planar tagged MR images

Denney

McVeigh

1997

Magnetic Resonance Imaging

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A technique is presented for reconstructing a three-dimensional myocardial strain map from a set of parallel-tagged MR images. Radial strains were reconstructed from in vivo data from an anesthetized dog with values between .05 and .1 with a precision of ± .003 for a tag detection accuracy of .1 mm and a tag spacing of 2.5 mm. The reconstruction spatial resolution was demonstrated by reconstructing a localized displacement abnormality. In the circumferential direction, the abnormality that resulted in 5O% displacement attenuation had a full width at half maximum of 5.4 ± .4 mm (mean ± SD). Graphs are presented showing the relationship between the size of an abnormality and the ability of the method to reconstruct that abnormality. The combination of high resolution parallel-tagged MR images and the model-free, coordinate system-free strain reconstruction technique presented in this paper is capable of producing accurate, high resolution strain maps of the myocardium. KeywordsCardiac MRI; Left ventricle; Cardiac mechanics; Spatial resolution Recent developments in MR tagging (1-9) make it possible to noninvasively measure the threedimensional motion of the heart wall. In tagged images, the myocardium appears with a spatially encoded pattern that moves with the tissue and can be analyzed to reconstruct the motion of the myocardium and measures of local contractile performance such as strain. Precise, quantitative measurements of myocardial function (strain) may allow clinicians to detect ischemia during stress testing with lower doses of inotropic agents. Also, the detection of functional recovery in stunned myocardium during low dose dobutamine infusion may be used to detect viable myocardium (10)(11)(12)(13)(14); this requires a technique that is very sensitive to small changes in myocardial strain. In this paper, we present a method for reconstructing a three-dimensional strain field of the left ventricle (LV) from a collection of tagged MR images.O'Dell et al (8) presented a three-dimensional strain reconstruction algorithm based on a prolate spheroidal basis function displacement model. This approach produces excellent results at the midwall, but careful preprocessing is required to get the heart in the correct coordinate system for reconstruction because the coordinate system foci and axes are critical to the reconstruction accuracy. Young et al (7,15) and Moulton et al (16) have developed three-dimensional strain reconstruction schemes based on a 16-element mesh and a piece-wise polynomial displacementCorrespondence to: Thomas S. Denney, Jr.. In this paper, we present a new model-free algorithm for reconstructing three-dimensional strain based on the discrete approach of Denney and Prince (9). The discrete model-free (DMF) algorithm decomposes the myocardial volume into a finely spaced mesh of points and reconstructs a high resolution three-dimensional displacement field using finite difference analysis and a smoothness constraint that minimizes the spatial variation of displacement across the myoc...

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Section: Spatial Coordinate Displacement Fitmentioning

confidence: 99%

Section: Spatial Resolution Of the Dmf Strain Reconstructionmentioning

confidence: 99%

Model‐free reconstruction of three‐dimensional myocardial strain from planar tagged MR images

Denney

McVeigh

1997

Magnetic Resonance Imaging

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“…Since this technique was first described (1,2), several studies have used MRI tagging to measure regional myocardial function with multiphase myocardial strain in normal and diseased states (3)(4)(5)(6). Algorithms that are necessary to quantify strain and regional myocardial function are heavily dependent on the contrast between the tag lines and the myocardium.…”

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confidence: 99%

Myocardial tagging and strain analysis at 3 Tesla: Comparison with 1.5 Tesla imaging

Valeti

Chun

Potter

et al. 2006

Magnetic Resonance Imaging

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Purpose: To determine whether imaging at 3 T could improve and prolong the tag contrast compared to images acquired at 1.5 T in normal volunteers, and whether such improvement would translate into the ability to perform strain measurements in diastole. Materials and Methods:Normal volunteers (N ϭ 13) were scanned at 1.5 T (GE Signa CV/i) and 3.0 T (GE VH/i). An ECG-triggered, segmented k-space, spoiled-gradient-echo grid-tagged sequence was used during cine acquisition. Tag contrast was determined by the difference of the mean signal intensity (SI) of the tagline to the mean SI of the myocardium divided by the standard deviation (SD) of the noise (CNR tag ). Matched short-axis (SA) slices were analyzed. Strain measurements were performed on images using a 2D strain analysis software program (harmonic phase (HARP)). Results:The average CNR tag over the cardiac cycle was superior at 3 T compared to 1.5 T for all slices (3 T: 23.4 Ϯ 12.1, 1.5 T: 9.8 Ϯ 8.4; P Ͻ 0.0001). This difference remained significant at cycle initiation, end-systole, and the end R-R interval (at cycle termination: 3 T ϭ 14.0 Ϯ 11.0 vs. 1.5 T ϭ 4.4 Ϯ 3.5; P Ͻ 0.01). Strain measures were obtainable only in early systole for 1.5 T images, but were robust throughout the entire R-R interval for 3 T images.Conclusion: Imaging at 3 T had a significant benefit for myocardial tag persistence through the cardiac cycle. The improvement allowed strain analysis to be performed into diastole. MYOCARDIAL TAGGING using MRI is an evolving noninvasive technique for assessing and quantifying regional myocardial function and strain in the human heart. Since this technique was first described (1,2), several studies have used MRI tagging to measure regional myocardial function with multiphase myocardial strain in normal and diseased states (3-6). Algorithms that are necessary to quantify strain and regional myocardial function are heavily dependent on the contrast between the tag lines and the myocardium. However, myocardial tagging techniques are limited by the rapid fading of tags, which restricts their application to the systolic phases of the cardiac cycle. Given the increasing recognition of the role of diastolic dysfunction in several cardiac disease states (7), it would be of clinical value to overcome the limitations posed by the early decay tags and extend the analysis of regional myocardial function and strain to the entire cardiac cycle. Several methods, including complementary spatially modulated magnetization (CSPAMM) (8,9) and balanced free precession sequences (10,11) have been employed toward that end. Higher-field-strength imaging is becoming more common and provides another pathway to potentially improve tag persistence through prolonged T1 myocardial recovery and enhanced signal-tonoise ratio (SNR).The aim of this study was to compare tag contrast as a function of time within the cardiac cycle in normal volunteers imaged at both 1.5 T and 3 T using a fast spoiled-gradient-recalled echo sequence with spatial modulation of magnetization. The images...

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“…Tagged MR imaging is a widely applied method for making high resolution, dynamic measurements of displacement in the human heart (Axel and Dougherty, 1989;Osman et al, 2000). Tagged MR images have sinusoidal modulations of intensity which appear as grids of "tag lines" that move with the material and can be tracked by a wealth of image analysis techniques (McVeigh, 1995, Axel and Dougherty, 1989, Osman et al, 2000. Tag lines are obtained non-invasively by using radiofrequency (RF) pulses and magnetic field gradients to impose variations in longitudinal magnetization of protons in the material (Axel and Dougherty, 1989).…”

Section: Introductionmentioning

confidence: 99%

Magnetic resonance measurement of transient shear wave propagation in a viscoelastic gel cylinder

Bayly

Massouros

Christoforou

et al. 2008

Journal of the Mechanics and Physics of Solids

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A magnetic resonance measurement technique was developed to characterize the transient mechanical response of a gel cylinder subjected to angular acceleration. The technique employs tagged magnetic resonance imaging (MRI) synchronized to periodic impact excitation of a bulk specimen. The tagged MRI sequence provides, non-invasively, an array of distributed displacement and strain measurements with high spatial (here, 5 mm) and temporal (6 ms) resolution. The technique was validated on a cylindrical gelatin sample. Measured dynamic strain fields were compared to strain fields predicted using (1) a closed-form solution and (2) finite element simulation of shear waves in a three-parameter "standard" linear viscoelastic cylinder subjected to similar initial and boundary conditions. Material parameters used in the analyses were estimated from measurements made on the gelatin in a standard rheometer. The experimental results support the utility of tagged MRI for dynamic, non-invasive assays such as measurement of shear waves in brain tissue during angular acceleration of the skull. When applied in the inverse sense, the technique has potential for characterization of the mechanical behavior of gel biomaterials.

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MR imaging of motion with spatial modulation of magnetization.

Cited by 1,072 publications

References 2 publications

Model‐free reconstruction of three‐dimensional myocardial strain from planar tagged MR images

Model‐free reconstruction of three‐dimensional myocardial strain from planar tagged MR images

Myocardial tagging and strain analysis at 3 Tesla: Comparison with 1.5 Tesla imaging

Magnetic resonance measurement of transient shear wave propagation in a viscoelastic gel cylinder

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