Baron Paul, Deckers Roel, Bouwman Job G, Bakker Chris J G, de Greef Martijn, Viergever Max A, Moonen Chrit T W, Bartels Lambertus W
Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands.
Magn Reson Med. 2016 Mar;75(3):1187-97. doi: 10.1002/mrm.25727. Epub 2015 May 2.
To investigate the effect of the aqueous and fatty tissue magnetic susceptibility distribution on absolute and relative temperature measurements as obtained directly from the water/fat (w/f) frequency difference.
Absolute thermometry was investigated using spherical phantoms filled with pork and margarine, which were scanned in three orthogonal orientations. To evaluate relative fat referencing, multigradient echo scans were acquired before and after heating pork tissue via high-intensity focused ultrasound (HIFU). Simulations were performed to estimate the errors that can be expected in human breast tissue.
The sphere experiment showed susceptibility-related errors of 8.4 °C and 0.2 °C for pork and margarine, respectively. For relative fat referencing measurements, fat showed pronounced phase changes of opposite polarity to aqueous tissue. The apparent mean temperature for a numerical breast model assumed to be 37 °C was 47.2 ± 21.6 °C. Simulations of relative fat referencing for a HIFU sonication (ΔT = 29.7 °C) yielded a maximum temperature error of 6.6 °C compared with 2.5 °C without fat referencing.
Variations in the observed frequency difference between water and fat are largely due to variations in the w/f spatial distribution. This effect may lead to considerable errors in absolute MR thermometry. Additionally, fat referencing may exacerbate rather than correct for proton resonance frequency shift-temperature measurement errors.
研究水性和脂肪组织的磁化率分布对直接从水/脂肪（w/f）频率差获得的绝对温度和相对温度测量的影响。
使用填充有猪肉和人造黄油的球形体模进行绝对温度测量，在三个正交方向上对其进行扫描。为了评估相对脂肪参考，在通过高强度聚焦超声（HIFU）加热猪肉组织之前和之后进行多梯度回波扫描。进行模拟以估计在人体乳腺组织中可能出现的误差。
球体实验表明，猪肉和人造黄油与磁化率相关的误差分别为8.4℃和0.2℃。对于相对脂肪参考测量，脂肪显示出与水性组织极性相反的明显相位变化。假定为37℃的数字乳腺模型的表观平均温度为47.2±21.6℃。对HIFU超声处理（ΔT = 29.7℃）的相对脂肪参考进行模拟，与不进行脂肪参考时的2.5℃相比，产生的最大温度误差为6.6℃。
水和脂肪之间观察到的频率差变化主要归因于w/f空间分布的变化。这种效应可能导致绝对磁共振测温中出现相当大的误差。此外，脂肪参考可能会加剧而不是纠正质子共振频率偏移 - 温度测量误差。
