利用不同設定的參數 b 值估計體素內不同調運動磁共振肝臟造影的微灌流參數

Abstract

本篇研究的目的是要探討使用不同調運動磁共振影像(IVIM)這項技術時, 在不同設定的低 b 因子之下,對於量測人體肝臟不同調流體擴散係數(D*)的影 響。此研究經人體試驗審查委員會核准,使用飛利浦 3 特斯拉的磁共振儀進行 14 位(男/女 6/8, 平均年齡 26.81±4.62 歲)受試者的掃描。實驗收取了 16 個 b 值(0, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 400, 800 s/mm2) 下的影像,並使用呼 吸導航降低呼吸運動對實驗的影響。利用 Matlab 軟體,自制非線性最小二乘法 (NLLS fitting)之程式,將不同 b 值之下收取到的信號強度套入 IVIM 的雙指數 衰減公式,進而得到三個 IVIM 的參數。實驗結果顯示,使用不同數目的低 b 值做 擬合計算時,會計算出不同數值的 IVIM 參數。造成計算所得的 IVIM 參數不穩定 的原因,可能為低訊雜比,呼吸運動的影響,或其他不確定因素。模擬的實驗結 果指出若影像訊雜比低於 50,就可能無法得到穩定的 D*參數。為了能得到可重復 性更好的 IVIM 參數,訊雜比的增強及呼吸調控的方法是未來可以再討論的主題。

The purpose of this study was to investigate the effects of low b-value settings on the estimation of pseudo-diffusion coefficient D* in human liver IVIM MR imaging. In this IRB approved study, 14 subjects (M/F 6/8, mean age 26.81±4.62 y) underwent IVIM diffusion-weighted magnetic resonance imaging on a Philip 3T scanner using sixteen b values (0, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 400, 800 s/mm2) with navigator to reduce influences from respiratory motion. Signals as a function of b-value were used to derive three parameters in IVIM equation by nonlinear least squared (NLLS) fitting. All data processing was carried out by self-designed Matlab scripts in bi-exponential decay equation. The results showed that using different number of low b values would obtain different calculated IVIM parameters. The reason of unstable results in calculated IVIM parameters may be caused by low signal to noise ratio (SNR), respiration control method, or other uncertain factors. Simulation results showed that D* were not stable if SNR is under 50. The improvement of SNR and breathing control could be further discussed to obtain more reproducible IVIM parameters.