Royal Marsden Hospital and Institute of Cancer Research, Downs Road, Sutton, Surrey, SM2 5PT, UK.
NMR Biomed. 2012 Jun;25(6):859-65. doi: 10.1002/nbm.1802. Epub 2011 Dec 22.
Increased expression of choline kinase has frequently been shown in tumours and is thought to be associated with disease progression. Studies using magnetic resonance spectroscopy have shown an increase in total choline-containing metabolites (tCho) in tumour compared with healthy tissue. Subsequent reductions in tCho following successful treatment support the use of tCho as a biomarker of disease and response. However, accurate measurement of tCho using MRS in abdominal tumours is complicated by respiratory motion, blurring the acquisition volume and degrading the lineshape and signal-to-noise ratio (SNR) of metabolites. Motion compensation using prospectively gated acquisitions or offline correction of phase and frequency distortions can help restore the SNR and linewidth of metabolites. Prospectively gated acquisitions have the advantage of confining the volume of acquisition to the prescribed volume but are constrained by the repetition time (TR) of the respiratory motion. In contrast, data acquired for offline correction may use a shorter repetition time and therefore yield an increased SNR per unit time. In this study abdominal spectra acquired from single-voxel 'free-breathing' measurements in liver of healthy volunteers and in abdominal tumours of cancer patients were compared with those of prospective gating and with an implementation of offline correction. The two motion compensation methodologies were assessed in terms of SNR, linewidth and repeatability. Our experiments show that prospective gating and offline correction result in a 12-22% reduction in median tCho linewidth, while offline correction also provides a significant increase in SNR. The repeatability coefficient (the expected interval for 95% of repeat measurements) for tCho/water ratio was reduced by 37% (prospective gating) and 41% (offline correction). Both methods of motion compensation substantially improved the reproducibility of the tCho/water measurement and the tCho linewidth. While offline correction also leads to a significant improvement in SNR, it may suffer more from out-of-voxel contamination.
胆碱激酶的表达增加在肿瘤中经常被发现，并且被认为与疾病进展有关。磁共振波谱研究表明，肿瘤中总含胆碱代谢物（tCho）的增加与健康组织相比。成功治疗后 tCho 的后续减少支持将 tCho 用作疾病和反应的生物标志物。然而，由于呼吸运动，腹部肿瘤中使用 MRS 对 tCho 进行准确测量变得复杂，呼吸运动会使采集体积模糊，并降低代谢物的线形状和信噪比（SNR）。使用前瞻性门控采集或离线相位和频率失真校正来进行运动补偿有助于恢复代谢物的 SNR 和线宽。前瞻性门控采集具有将采集体积限制在规定体积内的优势，但受到呼吸运动重复时间（TR）的限制。相比之下，用于离线校正的数据可能使用较短的重复时间，从而在单位时间内产生更高的 SNR。在这项研究中，比较了来自健康志愿者肝脏的单体素“自由呼吸”测量和癌症患者腹部肿瘤的腹部光谱与前瞻性门控采集和离线校正的实施。从 SNR、线宽和重复性三个方面评估了这两种运动补偿方法。我们的实验表明，前瞻性门控采集和离线校正可使 tCho 线宽的中位数降低 12-22%，而离线校正还可显著提高 SNR。tCho/水比的重复性系数（95%重复测量的预期间隔）降低了 37%（前瞻性门控采集）和 41%（离线校正）。这两种运动补偿方法都大大提高了 tCho/水测量和 tCho 线宽的重现性。虽然离线校正也可显著提高 SNR，但它可能更容易受到体素外污染的影响。
