Through-plane dark-rim artefacts in 3D first-pass myocardial perfusion
Journal of Cardiovascular Magnetic Resonance volume 17, Article number: P100 (2015)
The dark-rim artefact (DRA) is well known in 2D first-pass perfusion (FPP). The in-plane features of DRA are understood, but DRA has not been examined along the second phase-encoding (partition) direction for 3D FPP. The Gibbs contribution to DRAs in 2D FPP is minimised by finer resolution, but low through-plane resolutions of 3D FPP imply risk of partition axis DRAs. We investigated these new partition DRAs ("PDRAs") and partial volume effects due to coarse resolution of this direction.
Low-resolution data at typical 3D FPP parameters were subsampled from 3 high-resolution sources to study PDRAs. High in-plane resolution was maintained so that any changes arose only from through-plane effects. The subsampled number of partitions used in the reconstructions (Np) was varied to give a 2-32mm range of through-plane resolutions.
A numerical phantom modelled a conical LV at intensity ratio 5:2 (blood:myocardium at first pass peak). Np, and the angle between endocardial wall and image plane, θB, were varied while plotting width of PDRAs.
In-vivo investigation: single-frame high-resolution data (1.3x1.3x2.0mm) was acquired by navigator-gated bSSFP at high flip-angle for similar blood:myocardium intensity ratio (approx 2:1).
LV blood and myocardium were manually segmented and the intensity of each tissue uniformly set to the 5:2 ratio of the numerical phantom. This gave more anatomically realistic data than the uniform cone, with changing θB along and around the LV.
Slice reconstructions (Fig 1) show overlapping consequences of increased PDRAs and partial volume (blurring) as slice thickness is increased. Arrows (1a) show PDRA in the 8-partition image coming through-plane, n.b. not an in-plane DRA. Variation of θB and Np in the conical phantom significantly altered PDRA width (Fig 2), with strongest artefacts at combined low resolution and sharp θB. Although the border is sharpest at θB near 90°, this implies no variation between planes and therefore no PDRA. Whilst PDRA width increases at coarser resolution, the simultaneous impact of partial volume at lower Np counteracts this effect. Eventually the blurring dominates and destroys endocardial border visibility. This pattern was seen in conical and anatomical phantoms (Fig 1a&b) and to some extent in-vivo (Fig 1c), although complicated by intensity slopes and effects beyond the LV. For some values of θB examined (~>65°) that may well occur in-vivo, sufficiently high through-plane resolution to avoid PDRAs is infeasible in 3D FPP; however, some compromise between PDRA and partial volume may be possible.
Contrary to expectation that increased resolution reduces DRAs, at the low through-plane resolutions of 3D FPP increasing the resolution in this direction may increase Gibbs-induced DRAs due to sharper through-plane boundaries. However, this is a trade-off against partial volume blurring at low partition resolution. Further in-vivo investigations should optimise compromise between these two effects.
Supported by the NIHR Cardiovascular Biomedical Research Unit of Royal Brompton and Harefield NHS Foundation Trust and Imperial College London, UK.
MF is funded by a British Heart Foundation (BHF) PhD Studentship Grant - FS/13/21/30143.
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Fair, M., Gatehouse, P. & Firmin, D. Through-plane dark-rim artefacts in 3D first-pass myocardial perfusion. J Cardiovasc Magn Reson 17 (Suppl 1), P100 (2015). https://doi.org/10.1186/1532-429X-17-S1-P100