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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

Equatorial septal ROI distributions of angle differences between the ST and DTI vectors/orientation angles. A – deviation angles /∠v3STe3DTI/ and /∠v2STe2DTI/ are shown, alongside the corresponding distributions of /∠β’v3STβ’e3DTI/, /∠β”v3STβ”e3DTI/, /∠β’v2STβ’e2DTI/, /∠β”v2STβ”e2DTI/. B – deviation angles /∠v1STe1DTI/ and /∠v1STe1DTI/ are shown, alongside the corresponding distributions of /∠α’v1STα’e1DTI/, /∠α”v1STα”e1DTI/. DTI: Scan #1, 6-direction, b = 1000 s/mm2; ST: Scan #8; DTW = 3; STW = 3. FLASH: fast low angle shot; ST: structure tensor of FLASH data; DTI: diffusion tensor magnetic resonance imaging; DTW: derivative template width STW: smoothing template width; MAD: median absolute deviation; ROI: region(s) of interest. The symbols for vectors and derived angles are defined in Table 2. The corresponding distributions for the equatorial lateral ROI are in Additional file 7: Figure DS3.
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Fig10: Equatorial septal ROI distributions of angle differences between the ST and DTI vectors/orientation angles. A – deviation angles /∠v3STe3DTI/ and /∠v2STe2DTI/ are shown, alongside the corresponding distributions of /∠β’v3STβ’e3DTI/, /∠β”v3STβ”e3DTI/, /∠β’v2STβ’e2DTI/, /∠β”v2STβ”e2DTI/. B – deviation angles /∠v1STe1DTI/ and /∠v1STe1DTI/ are shown, alongside the corresponding distributions of /∠α’v1STα’e1DTI/, /∠α”v1STα”e1DTI/. DTI: Scan #1, 6-direction, b = 1000 s/mm2; ST: Scan #8; DTW = 3; STW = 3. FLASH: fast low angle shot; ST: structure tensor of FLASH data; DTI: diffusion tensor magnetic resonance imaging; DTW: derivative template width STW: smoothing template width; MAD: median absolute deviation; ROI: region(s) of interest. The symbols for vectors and derived angles are defined in Table 2. The corresponding distributions for the equatorial lateral ROI are in Additional file 7: Figure DS3.

Mentions: In Figure 9 the putative laminar normal β’ angles are colored (on the −90° to +90° color scale) for an equatorial short-axis slice from 5 rat hearts, after whole-heart registration. The corresponding FLASH images of laminar architecture are shown for comparison. The equivalent visualizations of β” angles are in Additional file 6: Figure DS2 (see Additional file 1: Supplemental Results). As for the 3D visualization in Figure 6, it is clear from inspection that there are similarities between the sheetlet orientation maps from DTI and from ST, but also areas of difference. To quantitatively investigate these observed differences between ST and DTI myolaminar orientation, the absolute differences between the putative sheetlet-normal eigenvectors and derived orientations (v3ST, β’v3ST, β”v3ST; and e3DTI, β’e3DTI, β”e3DTI) and the sheetlet in-plane vectors and angles are explored in rose diagrams for the septal ROI from one heart in Figure 10A. The properties of the sheetlet in-plane vectors and angles are discussed in the results supplement. As the myolaminar vectors are axial (their orientation is in the range of 180°) the angle difference between them is in the range 0 - 90°. Therefore, the angle difference plots are quadrant rose diagrams. These statistical diagrams have the following key characteristics: (i) for near-identical distributions they are narrow and centered at 0°; (ii) measures with large systematic error exhibit narrow distributions that are not centered at 0°; and, (iii) for randomly associated vectors the distributions are evenly spread across the 0 - 90° range of the quadrant. The center is represented by the median, and the spread by the median absolute deviation (MAD). Associated rose diagrams for the lateral ROI are in the Additional file 7: Figure DS3 (Additional file 1). /∠v3STe3DTI/ has a spread out distribution skewed towards lower values, (median ± MAD: 27.9 ± 17.4°). The same pattern is observed in the derived sheetlet-normal elevation angles /∠β’v3STβ’e3DTI/, but the differences are less marked. It can be seen that the general properties of the angle difference of the vector are also observed in the distributions of the elevation and transverse angles. The patterns described for the septal ROI are also observed in the lateral ROI (Additional file 7: Figure DS3A), but to a lesser degree. The local myocyte-orientation vector comparisons in Figure 10B and Additional file 7: Figure DS3B are discussed later in the manuscript.Figure 10


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)

Equatorial septal ROI distributions of angle differences between the ST and DTI vectors/orientation angles. A – deviation angles /∠v3STe3DTI/ and /∠v2STe2DTI/ are shown, alongside the corresponding distributions of /∠β’v3STβ’e3DTI/, /∠β”v3STβ”e3DTI/, /∠β’v2STβ’e2DTI/, /∠β”v2STβ”e2DTI/. B – deviation angles /∠v1STe1DTI/ and /∠v1STe1DTI/ are shown, alongside the corresponding distributions of /∠α’v1STα’e1DTI/, /∠α”v1STα”e1DTI/. DTI: Scan #1, 6-direction, b = 1000 s/mm2; ST: Scan #8; DTW = 3; STW = 3. FLASH: fast low angle shot; ST: structure tensor of FLASH data; DTI: diffusion tensor magnetic resonance imaging; DTW: derivative template width STW: smoothing template width; MAD: median absolute deviation; ROI: region(s) of interest. The symbols for vectors and derived angles are defined in Table 2. The corresponding distributions for the equatorial lateral ROI are in Additional file 7: Figure DS3.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
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Fig10: Equatorial septal ROI distributions of angle differences between the ST and DTI vectors/orientation angles. A – deviation angles /∠v3STe3DTI/ and /∠v2STe2DTI/ are shown, alongside the corresponding distributions of /∠β’v3STβ’e3DTI/, /∠β”v3STβ”e3DTI/, /∠β’v2STβ’e2DTI/, /∠β”v2STβ”e2DTI/. B – deviation angles /∠v1STe1DTI/ and /∠v1STe1DTI/ are shown, alongside the corresponding distributions of /∠α’v1STα’e1DTI/, /∠α”v1STα”e1DTI/. DTI: Scan #1, 6-direction, b = 1000 s/mm2; ST: Scan #8; DTW = 3; STW = 3. FLASH: fast low angle shot; ST: structure tensor of FLASH data; DTI: diffusion tensor magnetic resonance imaging; DTW: derivative template width STW: smoothing template width; MAD: median absolute deviation; ROI: region(s) of interest. The symbols for vectors and derived angles are defined in Table 2. The corresponding distributions for the equatorial lateral ROI are in Additional file 7: Figure DS3.
Mentions: In Figure 9 the putative laminar normal β’ angles are colored (on the −90° to +90° color scale) for an equatorial short-axis slice from 5 rat hearts, after whole-heart registration. The corresponding FLASH images of laminar architecture are shown for comparison. The equivalent visualizations of β” angles are in Additional file 6: Figure DS2 (see Additional file 1: Supplemental Results). As for the 3D visualization in Figure 6, it is clear from inspection that there are similarities between the sheetlet orientation maps from DTI and from ST, but also areas of difference. To quantitatively investigate these observed differences between ST and DTI myolaminar orientation, the absolute differences between the putative sheetlet-normal eigenvectors and derived orientations (v3ST, β’v3ST, β”v3ST; and e3DTI, β’e3DTI, β”e3DTI) and the sheetlet in-plane vectors and angles are explored in rose diagrams for the septal ROI from one heart in Figure 10A. The properties of the sheetlet in-plane vectors and angles are discussed in the results supplement. As the myolaminar vectors are axial (their orientation is in the range of 180°) the angle difference between them is in the range 0 - 90°. Therefore, the angle difference plots are quadrant rose diagrams. These statistical diagrams have the following key characteristics: (i) for near-identical distributions they are narrow and centered at 0°; (ii) measures with large systematic error exhibit narrow distributions that are not centered at 0°; and, (iii) for randomly associated vectors the distributions are evenly spread across the 0 - 90° range of the quadrant. The center is represented by the median, and the spread by the median absolute deviation (MAD). Associated rose diagrams for the lateral ROI are in the Additional file 7: Figure DS3 (Additional file 1). /∠v3STe3DTI/ has a spread out distribution skewed towards lower values, (median ± MAD: 27.9 ± 17.4°). The same pattern is observed in the derived sheetlet-normal elevation angles /∠β’v3STβ’e3DTI/, but the differences are less marked. It can be seen that the general properties of the angle difference of the vector are also observed in the distributions of the elevation and transverse angles. The patterns described for the septal ROI are also observed in the lateral ROI (Additional file 7: Figure DS3A), but to a lesser degree. The local myocyte-orientation vector comparisons in Figure 10B and Additional file 7: Figure DS3B are discussed later in the manuscript.Figure 10

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