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Temperature monitoring with line scan echo planar spectroscopic imaging
Author(s) -
McDannold Nathan,
Hynynen Kullervo,
Oshio Koichi,
Mulkern Robert V.
Publication year - 2001
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1350434
Subject(s) - imaging phantom , nuclear magnetic resonance , materials science , thermocouple , scanner , planar , voxel , echo planar imaging , temperature measurement , image resolution , magnetic resonance imaging , optics , physics , radiology , medicine , computer graphics (images) , quantum mechanics , computer science , composite material
A new magnetic resonance imaging method, line scan echo planar spectroscopic imaging (LSEPSI), is shown capable of providing rapid, internally referenced temperature monitoring from water and fat chemical shifts. Methods : Orthogonal 90° and 180° slice selective RF pulses inclined by 45° from the image plane solicit a spin echo from a tissue column. The echo is read by asymmetric sampling of 32 gradient echoes spaced 1.4–1.8 ms apart. Sixty‐four adjacent columns are sequentially sampled in 4.2–6.4 s with 4096 voxels sampled with voxel volumes of 0.08–0.13 cm 3 . Mixed mayonnaise/water phantoms were used to correlate LSEPSI‐derived chemical shifts and thermocouple‐based temperature measurements from 23 to 60 °C with a 1.5 T scanner. Measurement artifacts unrelated to temperature were investigated with the phantom, as was the feasibility of applying the sequence in human breast in vivo . Results : The correlation between LSEPSI and thermocouple‐based temperature measurements in the phantom was excellent( r 2 > 0.99 ) . Field drifts affecting the temperature measurements using the water peak alone were corrected by using the water/lipid peak difference. The sequence had an average temperature resolution of 1.4 °C in the phantom. The frequency difference measurement reduced the sensitivity to artifacts related to temperature. Both water and lipid peaks were detectable throughout many locations in the breast, suggesting the applicability of LSEPSI in this organ. Discussion : T1‐saturation losses occur in conventional and echo‐planar based 2D CSI sequences using phase encoding methods with short TR periods. These losses are eliminated when individual columns are sampled in snapshot fashion with LSEPSI since the effective TR becomes the time between scans rather than excitations. T1 saturation can make small spectral peaks difficult to detect at high temperatures and generally lowers the signal‐to‐noise ratio of the spectra. The rapid acquisition and insensitivity to T1 saturation effects make LSEPSI an attractive technique for monitoring thermal therapies in breast using the internally referenced fat/water frequency separation.