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Towards refining the definition of grey zone for late gadolinium enhancement
© Peters et al; licensee BioMed Central Ltd. 2010
Published: 21 January 2010
Grey zone on late gadolinium enhancement images (LGE) is quantified using signal intensity (SI) (1,2). However, LGE signal depends on heart-rate and TI choice, and the noise.
To demonstrate that grey zone and scar quantified on LGE depend on image SNR and inversion time (TI), and to use T1-mapping to assess the normal range of post-contrast T1 values in the heart, for improved detection of grey zone.
A collection of phantoms (505-302 ms T1s, in 50 ms increments) with known T1s were imaged using LGE sequences, with scan parameters: 1RR between inversions, TR/TE/θ = 5.7 ms/3.4 ms/20º, 1.5 × 1.5 × 5 mm, 20 views-per-segment, sequential order. The phantom with T1 = 505 ms represented "normal myocardium" and the phantom with T1 = 302 ms represented "scar". The myocardial signal was nulled, and scar and grey zone thresholds were calculated using 50% of maximal SI (2) in scar and maximal SI in the "normal myocardium" (2). The LGE sequence was acquired at higher SNR, and at optimal TI and optimal TI ± 30 ms.
An ECG-gated T1 map was obtained using the LGE multiple TI approach (3) in 3 healthy subjects and one patient (age 36 ± 19 years), 20-25 minutes after 0.2 mmol/kg injection of Gd-DTPA. A two-parameter non-linear least-squares fit was applied to the data in Matlab.
Grey zone characterization by LGE depends on SNR and appropriate TI. Using T1 mapping method, the range of T1s in normal subjects has been measured. T1-mapping in patients will be a step towards refining the identification of grey zone using thresholds based on regional T1 values.
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