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Comparison of diffusion tensor imaging by cardiovascular magnetic resonance and gadolinium enhanced 3D image intensity approaches to investigation of structural anisotropy in explanted rat hearts.

Bernus O, Radjenovic A, Trew ML, LeGrice IJ, Sands GB, Magee DR, Smaill BH, Gilbert SH - J Cardiovasc Magn Reson (2015)

Bottom Line: Both FLASH (v3(ST)) and DTI (e3(DTI)) where compared to directly measured laminar arrays in the FLASH images.We show that ST analysis of FLASH is a useful and accurate tool in the measurement of cardiac microstructure.While both FLASH and the DTI approaches appear promising for mapping of the alignments of myocytes throughout myocardium, marked discrepancies between the cross myocyte anisotropies deduced from each method call for consideration of their respective limitations.

View Article: PubMed Central - PubMed

Affiliation: Inserm U1045 - Centre de Recherche Cardio-Thoracique, L'Institut de rythmologie et modélisation cardiaque LIRYC, Université de Bordeaux, PTIB - campus Xavier Arnozan, Avenue du Haut Leveque, 33604, Pessac, France. olivier.bernus@u-bordeaux.fr.

ABSTRACT

Background: Cardiovascular magnetic resonance (CMR) can through the two methods 3D FLASH and diffusion tensor imaging (DTI) give complementary information on the local orientations of cardiomyocytes and their laminar arrays.

Methods: Eight explanted rat hearts were perfused with Gd-DTPA contrast agent and fixative and imaged in a 9.4T magnet by two types of acquisition: 3D fast low angle shot (FLASH) imaging, voxels 50 × 50 × 50 μm, and 3D spin echo DTI with monopolar diffusion gradients of 3.6 ms duration at 11.5 ms separation, voxels 200 × 200 × 200 μm. The sensitivity of each approach to imaging parameters was explored.

Results: The FLASH data showed laminar alignments of voxels with high signal, in keeping with the presumed predominance of contrast in the interstices between sheetlets. It was analysed, using structure-tensor (ST) analysis, to determine the most (v1(ST)), intermediate (v2(ST)) and least (v3(ST)) extended orthogonal directions of signal continuity. The DTI data was analysed to determine the most (e1(DTI)), intermediate (e2(DTI)) and least (e3(DTI)) orthogonal eigenvectors of extent of diffusion. The correspondence between the FLASH and DTI methods was measured and appraised. The most extended direction of FLASH signal (v1(ST)) agreed well with that of diffusion (e1(DTI)) throughout the left ventricle (representative discrepancy in the septum of 13.3 ± 6.7°: median ± absolute deviation) and both were in keeping with the expected local orientations of the long-axis of cardiomyocytes. However, the orientation of the least directions of FLASH signal continuity (v3(ST)) and diffusion (e3(ST)) showed greater discrepancies of up to 27.9 ± 17.4°. Both FLASH (v3(ST)) and DTI (e3(DTI)) where compared to directly measured laminar arrays in the FLASH images. For FLASH the discrepancy between the structure-tensor calculated v3(ST) and the directly measured FLASH laminar array normal was of 9 ± 7° for the lateral wall and 7 ± 9° for the septum (median ± inter quartile range), and for DTI the discrepancy between the calculated v3(DTI) and the directly measured FLASH laminar array normal was 22 ± 14° and 61 ± 53.4°. DTI was relatively insensitive to the number of diffusion directions and to time up to 72 hours post fixation, but was moderately affected by b-value (which was scaled by modifying diffusion gradient pulse strength with fixed gradient pulse separation). Optimal DTI parameters were b = 1000 mm/s(2) and 12 diffusion directions. FLASH acquisitions were relatively insensitive to the image processing parameters explored.

Conclusions: We show that ST analysis of FLASH is a useful and accurate tool in the measurement of cardiac microstructure. While both FLASH and the DTI approaches appear promising for mapping of the alignments of myocytes throughout myocardium, marked discrepancies between the cross myocyte anisotropies deduced from each method call for consideration of their respective limitations.

No MeSH data available.


Related in: MedlinePlus

ST and DTI putative sheetlet normal orientations compared voxel-wise to the FI normal (/∠ [v3ST/e3DTI]nFI/). These frequency distributions summarize the orientations from the interactively segmented sheetlets of Figure 3 for the lateral ROI (left) and for the septal ROI (right). A - distributions produced for the first set of imaging/image-processing parameters compared to FI (DTI: Scan #1, 6-direction, b = 1000 s/mm2; ST: Scan #8, DTW = 3, STW = 3). B - distributions for the second set of imaging/image-processing parameters compared to FI (DTI: Scan #2, 12-direction, b = 1000 s/mm2; ST: Scan #8, DTW = 5, STW = 5) allow assessment of sensitivity of the measured laminar normals to these parameters. Note: the deviation angles shown in these histograms are not on a circular scale as they are absolute values and 0° ≠ 90°. FLASH: fast low angle shot; ST: structure tensor of FLASH data; DTI: diffusion tensor magnetic resonance imaging; FI: FLASH isosurface data; DTW: derivative template width STW: smoothing template width. The symbols for vectors and derived angles are defined in Table 2.
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Fig7: ST and DTI putative sheetlet normal orientations compared voxel-wise to the FI normal (/∠ [v3ST/e3DTI]nFI/). These frequency distributions summarize the orientations from the interactively segmented sheetlets of Figure 3 for the lateral ROI (left) and for the septal ROI (right). A - distributions produced for the first set of imaging/image-processing parameters compared to FI (DTI: Scan #1, 6-direction, b = 1000 s/mm2; ST: Scan #8, DTW = 3, STW = 3). B - distributions for the second set of imaging/image-processing parameters compared to FI (DTI: Scan #2, 12-direction, b = 1000 s/mm2; ST: Scan #8, DTW = 5, STW = 5) allow assessment of sensitivity of the measured laminar normals to these parameters. Note: the deviation angles shown in these histograms are not on a circular scale as they are absolute values and 0° ≠ 90°. FLASH: fast low angle shot; ST: structure tensor of FLASH data; DTI: diffusion tensor magnetic resonance imaging; FI: FLASH isosurface data; DTW: derivative template width STW: smoothing template width. The symbols for vectors and derived angles are defined in Table 2.

Mentions: We compared ST and DTI laminar orientation measurement respectively against a direct interactive visualization approach (FI). It can be seen in the example voxel in Figure 3F that the laminar structure has a clearly defined simple orientation, and that v3ST is much closer than e3DTI to nFI (/∠v3STnFI/ = 7.8°; /∠e3DTInFI/ = 19.6°). This individual voxel comparison is for the purpose of illustrating the approach, and no conclusions can be drawn from this voxel alone. However, the same approach is visualized qualitatively in Figure 5, and then applied to quantify /∠v3STnFI/ and /∠e3DTnFI/ for the whole of the lateral and septal ROIs (Figure 7A).Figure 7


Comparison of diffusion tensor imaging by cardiovascular magnetic resonance and gadolinium enhanced 3D image intensity approaches to investigation of structural anisotropy in explanted rat hearts.

Bernus O, Radjenovic A, Trew ML, LeGrice IJ, Sands GB, Magee DR, Smaill BH, Gilbert SH - J Cardiovasc Magn Reson (2015)

ST and DTI putative sheetlet normal orientations compared voxel-wise to the FI normal (/∠ [v3ST/e3DTI]nFI/). These frequency distributions summarize the orientations from the interactively segmented sheetlets of Figure 3 for the lateral ROI (left) and for the septal ROI (right). A - distributions produced for the first set of imaging/image-processing parameters compared to FI (DTI: Scan #1, 6-direction, b = 1000 s/mm2; ST: Scan #8, DTW = 3, STW = 3). B - distributions for the second set of imaging/image-processing parameters compared to FI (DTI: Scan #2, 12-direction, b = 1000 s/mm2; ST: Scan #8, DTW = 5, STW = 5) allow assessment of sensitivity of the measured laminar normals to these parameters. Note: the deviation angles shown in these histograms are not on a circular scale as they are absolute values and 0° ≠ 90°. FLASH: fast low angle shot; ST: structure tensor of FLASH data; DTI: diffusion tensor magnetic resonance imaging; FI: FLASH isosurface data; DTW: derivative template width STW: smoothing template width. The symbols for vectors and derived angles are defined in Table 2.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4414435&req=5

Fig7: ST and DTI putative sheetlet normal orientations compared voxel-wise to the FI normal (/∠ [v3ST/e3DTI]nFI/). These frequency distributions summarize the orientations from the interactively segmented sheetlets of Figure 3 for the lateral ROI (left) and for the septal ROI (right). A - distributions produced for the first set of imaging/image-processing parameters compared to FI (DTI: Scan #1, 6-direction, b = 1000 s/mm2; ST: Scan #8, DTW = 3, STW = 3). B - distributions for the second set of imaging/image-processing parameters compared to FI (DTI: Scan #2, 12-direction, b = 1000 s/mm2; ST: Scan #8, DTW = 5, STW = 5) allow assessment of sensitivity of the measured laminar normals to these parameters. Note: the deviation angles shown in these histograms are not on a circular scale as they are absolute values and 0° ≠ 90°. FLASH: fast low angle shot; ST: structure tensor of FLASH data; DTI: diffusion tensor magnetic resonance imaging; FI: FLASH isosurface data; DTW: derivative template width STW: smoothing template width. The symbols for vectors and derived angles are defined in Table 2.
Mentions: We compared ST and DTI laminar orientation measurement respectively against a direct interactive visualization approach (FI). It can be seen in the example voxel in Figure 3F that the laminar structure has a clearly defined simple orientation, and that v3ST is much closer than e3DTI to nFI (/∠v3STnFI/ = 7.8°; /∠e3DTInFI/ = 19.6°). This individual voxel comparison is for the purpose of illustrating the approach, and no conclusions can be drawn from this voxel alone. However, the same approach is visualized qualitatively in Figure 5, and then applied to quantify /∠v3STnFI/ and /∠e3DTnFI/ for the whole of the lateral and septal ROIs (Figure 7A).Figure 7

Bottom Line: Both FLASH (v3(ST)) and DTI (e3(DTI)) where compared to directly measured laminar arrays in the FLASH images.We show that ST analysis of FLASH is a useful and accurate tool in the measurement of cardiac microstructure.While both FLASH and the DTI approaches appear promising for mapping of the alignments of myocytes throughout myocardium, marked discrepancies between the cross myocyte anisotropies deduced from each method call for consideration of their respective limitations.

View Article: PubMed Central - PubMed

Affiliation: Inserm U1045 - Centre de Recherche Cardio-Thoracique, L'Institut de rythmologie et modélisation cardiaque LIRYC, Université de Bordeaux, PTIB - campus Xavier Arnozan, Avenue du Haut Leveque, 33604, Pessac, France. olivier.bernus@u-bordeaux.fr.

ABSTRACT

Background: Cardiovascular magnetic resonance (CMR) can through the two methods 3D FLASH and diffusion tensor imaging (DTI) give complementary information on the local orientations of cardiomyocytes and their laminar arrays.

Methods: Eight explanted rat hearts were perfused with Gd-DTPA contrast agent and fixative and imaged in a 9.4T magnet by two types of acquisition: 3D fast low angle shot (FLASH) imaging, voxels 50 × 50 × 50 μm, and 3D spin echo DTI with monopolar diffusion gradients of 3.6 ms duration at 11.5 ms separation, voxels 200 × 200 × 200 μm. The sensitivity of each approach to imaging parameters was explored.

Results: The FLASH data showed laminar alignments of voxels with high signal, in keeping with the presumed predominance of contrast in the interstices between sheetlets. It was analysed, using structure-tensor (ST) analysis, to determine the most (v1(ST)), intermediate (v2(ST)) and least (v3(ST)) extended orthogonal directions of signal continuity. The DTI data was analysed to determine the most (e1(DTI)), intermediate (e2(DTI)) and least (e3(DTI)) orthogonal eigenvectors of extent of diffusion. The correspondence between the FLASH and DTI methods was measured and appraised. The most extended direction of FLASH signal (v1(ST)) agreed well with that of diffusion (e1(DTI)) throughout the left ventricle (representative discrepancy in the septum of 13.3 ± 6.7°: median ± absolute deviation) and both were in keeping with the expected local orientations of the long-axis of cardiomyocytes. However, the orientation of the least directions of FLASH signal continuity (v3(ST)) and diffusion (e3(ST)) showed greater discrepancies of up to 27.9 ± 17.4°. Both FLASH (v3(ST)) and DTI (e3(DTI)) where compared to directly measured laminar arrays in the FLASH images. For FLASH the discrepancy between the structure-tensor calculated v3(ST) and the directly measured FLASH laminar array normal was of 9 ± 7° for the lateral wall and 7 ± 9° for the septum (median ± inter quartile range), and for DTI the discrepancy between the calculated v3(DTI) and the directly measured FLASH laminar array normal was 22 ± 14° and 61 ± 53.4°. DTI was relatively insensitive to the number of diffusion directions and to time up to 72 hours post fixation, but was moderately affected by b-value (which was scaled by modifying diffusion gradient pulse strength with fixed gradient pulse separation). Optimal DTI parameters were b = 1000 mm/s(2) and 12 diffusion directions. FLASH acquisitions were relatively insensitive to the image processing parameters explored.

Conclusions: We show that ST analysis of FLASH is a useful and accurate tool in the measurement of cardiac microstructure. While both FLASH and the DTI approaches appear promising for mapping of the alignments of myocytes throughout myocardium, marked discrepancies between the cross myocyte anisotropies deduced from each method call for consideration of their respective limitations.

No MeSH data available.


Related in: MedlinePlus