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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

The putative ST and DTI myocyte angles are compared for 5 rat hearts. The putative myocyte helix angle α’ and transverse angle α” in an equatorial short-axis slice are colored according to the −90° to +90° scale shown. The transmural orange line on the FLASH images indicates the transmural span quantified in in Figure 14. 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. The symbols for vectors and derived angles are defined in Table 2.
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Fig13: The putative ST and DTI myocyte angles are compared for 5 rat hearts. The putative myocyte helix angle α’ and transverse angle α” in an equatorial short-axis slice are colored according to the −90° to +90° scale shown. The transmural orange line on the FLASH images indicates the transmural span quantified in in Figure 14. 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. The symbols for vectors and derived angles are defined in Table 2.

Mentions: The ST and DTI local myocyte angles were compared in 3D visualizations alongside the images of the FLASH images in Figure 6C and for a second heart in Additional file 9: Movie 3. The DTI local myocyte helix-angle (α’e1DTI) follows the familiar smooth transmural change in orientation from large positive angles at the endocardium (+65° ± 5°) to negative angles at the epicardium (−65° ± 20°) [8]. The smooth change is observed around the circumference of the short-axis slice and in the long-axis views from base to apex. There is greater noise in the ST than the DTI, both for α’ and α”. In Figure 13 the similarity between ST and DTI for both α’ and α” is across the entire short-axis slice. In Figure 6 this similarity between ST and DTI α’ and α” is across most of the long-axis view, however, there are also small regions of difference in α’ in the septal-apex, as identified with the black square in Figure 6C. This 3D qualitative analysis in one heart is extended to 2D qualitative analysis in five registered hearts in Figure 13. In Figure 13 α’e1DTI and α”e1DTI are visualized in the same equatorial short-axis slice for 5 hearts showing that: (i) α’e1DTI and α’v1ST are similar within individual rats; (ii) α”e1DTI and α”v1ST are similar within individual rats; (iii) α’ and α” are consistent between rat hearts, whether measured by ST (v1ST) or DTI (e1DTI); (iv) both α’e1DTI and α”e1DTI are very similar to rat α’e1DTI and α”e1DTI reported in the literature [39]. As observed in the single heart volumetric analysis (above, Figure 6C) the ST measured local myocyte angles are globally similar to the DTI local myocyte angles, and likewise, there is greater noise in the ST data than in the DTI data. There are no regions of large difference between α’v1ST to α’e1DTI in the equatorial slices (the identified region of difference in α’ in Figure 6C was limited to the apex).Figure 13


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)

The putative ST and DTI myocyte angles are compared for 5 rat hearts. The putative myocyte helix angle α’ and transverse angle α” in an equatorial short-axis slice are colored according to the −90° to +90° scale shown. The transmural orange line on the FLASH images indicates the transmural span quantified in in Figure 14. 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. The symbols for vectors and derived angles are defined in Table 2.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4414435&req=5

Fig13: The putative ST and DTI myocyte angles are compared for 5 rat hearts. The putative myocyte helix angle α’ and transverse angle α” in an equatorial short-axis slice are colored according to the −90° to +90° scale shown. The transmural orange line on the FLASH images indicates the transmural span quantified in in Figure 14. 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. The symbols for vectors and derived angles are defined in Table 2.
Mentions: The ST and DTI local myocyte angles were compared in 3D visualizations alongside the images of the FLASH images in Figure 6C and for a second heart in Additional file 9: Movie 3. The DTI local myocyte helix-angle (α’e1DTI) follows the familiar smooth transmural change in orientation from large positive angles at the endocardium (+65° ± 5°) to negative angles at the epicardium (−65° ± 20°) [8]. The smooth change is observed around the circumference of the short-axis slice and in the long-axis views from base to apex. There is greater noise in the ST than the DTI, both for α’ and α”. In Figure 13 the similarity between ST and DTI for both α’ and α” is across the entire short-axis slice. In Figure 6 this similarity between ST and DTI α’ and α” is across most of the long-axis view, however, there are also small regions of difference in α’ in the septal-apex, as identified with the black square in Figure 6C. This 3D qualitative analysis in one heart is extended to 2D qualitative analysis in five registered hearts in Figure 13. In Figure 13 α’e1DTI and α”e1DTI are visualized in the same equatorial short-axis slice for 5 hearts showing that: (i) α’e1DTI and α’v1ST are similar within individual rats; (ii) α”e1DTI and α”v1ST are similar within individual rats; (iii) α’ and α” are consistent between rat hearts, whether measured by ST (v1ST) or DTI (e1DTI); (iv) both α’e1DTI and α”e1DTI are very similar to rat α’e1DTI and α”e1DTI reported in the literature [39]. As observed in the single heart volumetric analysis (above, Figure 6C) the ST measured local myocyte angles are globally similar to the DTI local myocyte angles, and likewise, there is greater noise in the ST data than in the DTI data. There are no regions of large difference between α’v1ST to α’e1DTI in the equatorial slices (the identified region of difference in α’ in Figure 6C was limited to the apex).Figure 13

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