【作者】 武志峰；

【导师】 周翔平；

【作者基本信息】 四川大学 ， 影像医学， 2005， 博士

【摘要】 磁共振功能成像是一种很有发展潜力的成像方式,它能利用非侵袭性的方式了解脏器的功能状态。常见的方法有弥散成像及灌注成像等。此类成像方法的临床应用之所以受到一定程度的限制,主要是针对活动器官(如肾脏)进行检查时较难获得可信度高、重复性强的数据,甚至对此类检查中所观察到的信号变化的生理学基础还没有彻底了解。 磁共振弥散加权成像(Diffusion-Weighted Imaging DWI)对分子的弥散运动——布朗运动非常敏感,正是分子的这种随机运动可以在梯度场中产生相位转变从而引起磁共振信号的变化。LeBihant等不仅将这种原理拓展到人的体内环境中,还总结出这种随机运动在体素内表达的模式。这种模式包括多种因素,最主要的是微血管的灌注和水分子的弥散。理论上,可以借助测量表观弥散系数(Apparent Diffusion Coefficient ADC)来综合评价体内微血管的灌注及水分子弥散。 由于弥散加权成像对运动特别敏感,其在人体内的应用受到较大的限制。起初,该技术主要应用于颅脑,其对脑缺血性病变非常敏感。随着回波平面成像(Echo-Planar Imaging EPI)的出现,磁共振弥散加权成像开始在腹部应用。 由于肾脏具有对水的重吸收、浓缩及稀释等功能,所以水的转运就成为肾脏的突出表现,同时肾脏血流灌注量也非常之大。另一方面,肾脏又是结构和功能联系非常紧密的脏器。所以在弥散成像中测量肾脏的ADC值有望对多种肾脏疾病(如慢性肾功能不全,尿路梗阻等)的发病更多还原

【Abstract】 Functional magnetic resonance imaging (FMRI) , such as diffusion weighted imaging(DWI) or perfusion weighted imaging(PWI), has a great potential of development as its manifesting the function of organ noninvasively. Its limitations in clinical applications are due to the difficulties in obtaining reproducible and reliable information in mobile organs (such as kidney). It is also because of less understanding of the physiologic principle for the signal changes observed.MR Diffusion-Weighted Imaging (DWI) is sensitive to molecular diffusion, known as Brownian motion. Since random motion in the field gradients produces in coherent phase shifts that result in signal attenuation. LeBihant et al extended these concepts to the in vivo situation and generalized the types of random motion that occur in tissues in the intravoxel-incoherent motion model. This model consists of many contents such as capillary perfusion and water diffusion. It is theoretically possible to evaluate the combined effects of capillary perfusion and water diffusion in vivo by an apparent diffusion coefficient (ADC).Because of its severe motion sensitivity, DWI in vivo has largely been restricted to the brain at the beginning. It has been accepted that diffusionmeasurements are highly sensitive to ischemia. With the use of echo-planar imaging (EPI), diffusion measurement can be obtained in abdomen.As its function of water reabsorption, concentration and dilution, the kidney shows its significant character as water-transportation. It is also an organ with high blood perfusion. In the other side, the structure and function of kidney are closely linked. Consequently, the measurement of the diffusion characteristics of the kidney in DWI may provide useful insights of the mechanisms of various renal diseases including chronic renal failure, ureteral obstruction and so on.Our study presents a retrospective analysis of 127 people (some were excluded because of no follow-up or bad imaging quality, only 86 cases left) with/without renal diseases at the department of radiology, west china hospital, sichan university, from September 2004 to January 2005.In the first part, the technology of kidney DWI had been studied. The parameters were established as: (1) People underwent DWI in a dehydrated state (with fasting for 6-hour). (2) The diffusion-sensitizing gradients were applied along 6 different directions. (3) Four b-values (0, 50, 100 and 400 s/mm ) in each direction were selected for isotropic parameter. (4) Breath trigger had been used. (5) The other parameters were as flow: TR, 2000 ms; TE, 70 ms; Fov, 390 mm; Slice thickness, 5 mm; Noise level, 40. Bandwidth, 1502 HZ; Phase encipher direction A?P.In the second part, to study of ADC values of healthy people, 15 volunteers (9 men, 6 women , ages 29 68 years , mean 46. 9 + 4. 5 years ) underwent DWI in a dyhydrated state .ADC values of each kidney were measured. Then Statistical analysis of ADC measurements for this group wasperformed. The average ADC values were 405.366X10 smm2 (for b50); 339.646 X 10 W ( for blOO ). 254.532 X 1O’W( forb400).In the third part, 8 hypertensive (6 men, 2 women, ages 38-65 years, mean 51.4±2.1 years) with the history more than 5 years underwent DWI. The parameters of examination and the method of measure were the same as before. The results showed that ADC values of this group were significantly lower than those of healthy group (b50), but for blOO and b400, there were considerable overlap in ADC values of two groups.In the fourth part, two groups patients underwent the examination. Group one: 12 patients (10 men, 2 women, ages 30-70 yeas, mean 51.2±5.1 yeas) diagnosed as chronic kidney disease (CKD) with CREA normal. Group two:20 patients (12 men, 8 women, ages 26 — 70, mean 50.1±4.8 yeas) confirmed of chronic renal failure(CRF) with serum creatinine(Scr) increased in different degree. ADC values of kidneys with CKD and CRF were all lower than those of the normal kidneys (b50 and b400). But for the latter, it showed a more significant trend. There was a weak linear correlation between ADC values and their clear creatinine rat (Ccr).In the fifth part, 14 patients with unilateral hydronephrosis (7 men, 7 women, ages 26-83 yeas, mean 55.4±3.5 years) were examined with diffusion-weighted imageing. ADC values were decreased in the kidneys with ureter obstruction and slightly increased in the contra-lateral kidneys.The sixth part was the last part of this study. In this part, a primary analysis of the character of lesions in DWI was probed, such as renal cancer, renal simple cyst and renal tuberculous pyonephrosis etc. It shows that MR DWI is a useful technique in differentiating these diseases.In conclusion, DWI and the measurement of ADC values are a noninvasive way of evaluating the functional state of the kidney and of differentiating various renal diseases, and it also have some potential values in other aspects.更多还原