兔肝脏纤维化模型CT灌注成像参数变化实验研究

目的 研究CT灌注成像参数在兔肝脏纤维化模型中变化情况.材料与方法 新西兰大白兔4只为对照组,兔肝脏纤维化模型13只,对其进行CT灌注成像扫描,以肝脏病理组织学评分分级和纤维化分期为标准,研究分析CT灌注参数变化.采用单向方差分析方法 ,P＜0.05为差异有统计学意义.结果 与正常对照组相比较,全部CT灌注成像参数在肝脏纤维化分期方面差异均有统计学意义(P＜0.05);血流量(BF)、血容量(BV)、肝动脉灌注指数(HAI)、肝动脉灌注量(BFA)测量结果 在病理评分分级方面差异有统计学意义(P＜0.05);平均通过时间(MTT)、毛细血管通透性表面积乘积(PS)和门静脉灌注量(BFP)在病理评分分级方面差异无统计学意义(P＞0.05).结论 在肝脏纤维化时BF、BV、HAI和BFA值明显低于正常对照组,且随着肝脏病理变化的进展和纤维化分期的增加BF、BV、和BFP值下降越加明显.形成这一变化的病理基础为Disse间隙内大量胶原纤维沉积、窦状间隙变小、伴有肝细胞肿胀、炎性浸润、肝细胞再生和假小叶形成等,使得肝内血管阻力升高,导致肝脏血流量减少.     

256层CT全肝灌注评估肝硬化段性功能储备

目的:以临床Ch ild-pug h分级为标准,应用256层CT全肝灌注扫描对肝硬化患者行段性功能储备评估。方法:20例无明显肝脏疾患的患者及23例肝硬化患者均行全肝灌注检查,得到肝脏灌注图像,分别测量肝脏各段灌注参数:肝动脉灌注量(HAP)、门静脉灌注量(HPP)、肝总灌注量(TLP)、肝动脉灌注指数(HAPI)以及门静脉灌注指数(HPPI)。对正常组及肝硬化组行肝段性灌注测量,对肝脏各段血流灌注参数行统计学分析。结果:正常肝脏各段间HAP、HPP、TLP、HAPI、HPPI均无统计学差异,HAP:HPP=1/3~1/4;Ch ild-pug h A级H A P、T LP存在段间差异(P<0.05),H A P:H PP=1/2~1/3;Ch ild-pug h B级H A P存在段间差异(P<0.05),HAP:HPP=1/2~1/3;Child-pugh C级各灌注参数均存在段间差异(P<0.05),HAP:HPP=2/1~2/3。正常组与肝硬化各组间比较:除Ⅱ、Ⅲ段HAP组间无统计学差异外,Ⅰ-Ⅷ段各灌注参数均存在部分组间差异(P<0.05),Ⅰ-Ⅷ段HPP肝硬化各组与正常组均有统计学差异,随着肝功能受损程度的加重,肝脏各段HAP、HAPI值呈上升趋势,HPP、TLP、HPPI值呈下降趋势,肝动脉与门静脉系统血供比例逐渐增大。结论:256层CT全肝灌注模式可用于直观定量反映肝硬化肝脏各段血流灌注特征,对肝脏储备功能分段评估具有一定临床应用价值。     

肝硬化的多层螺旋CT灌注成像表现

目的 探讨肝硬化的多层螺旋CT灌注成像表现.方法 对25例肝硬化患者及12例健康成人作为对照者行肝脏16层螺旋CT灌注成像,得到肝脏血流灌注参数值,并与Child分级相对照.结果 与正常对照组比较,随着肝硬化程度的加重,肝脏的血流量(BF)、血容量(BV)逐渐降低,肝动脉分数(HAF)逐渐增高;平均通过时间(MTT)未见明确变化规律.结论 CT灌注成像有助于早期诊断肝硬化,而且可以用于评价肝硬化病变程度,具有一定的临床意义.     

CT灌注成像在胃癌诊断中的临床应用

目的探讨胃癌CT灌注特点及具体灌注参数值和CT灌注成像在胃癌诊断中的临床应用价值。方法对经内镜病理确诊的50例胃癌和20例正常胃(对照组)行64层螺旋CT灌注成像检查,对所得容积数据采用CT灌注软件包的腹部肿瘤灌注协议(去卷积法)进行计算、制图和分析,分别测取血流量(BF)、血容量(BV)、平均通过时间(MTT)和毛细血管表面通透性(PS)四个参数值,然后应用SPSSl7.0软件进行统计分析。结果正常胃的BF、BV、MTT和PS平均值分别为75.0717.08ml/(min.100g)、7.951.81ml/100g、16.672.40s和7.981.30ml/(min.100g);胃癌的BF、BV、MTT和PS平均值分别为101.2848.01ml/(min.100g)、16.096.23ml/100g、9.574.99s和33.0023.27ml/(min.100g);两组比较,胃癌BF、BV、PS值升高,而MTT值下降,四个灌注参数值差异均具有非常显著的统计学意义(P0.01)。结论胃CT灌注成像是一种功能成像,从血流动力学角度对胃癌的临床诊疗有一定价值。     

CT 灌注成像对胃癌评估的临床应用

目的：探讨 CT 灌注成像参数值与不同分化程度胃癌的相关性。方法应用64层螺旋 CT 对经手术病理证实的50例胃癌患者术前行灌注成像检查,获得灌注参数值,包括血流量(BF)、血容量(BV)、平均通过时间(MTT)和毛细血管表面通透性(PS);根据肿瘤细胞不同分化程度分成高、中、低分化3组,然后应用 SPSS 17.0软件进行统计分析。结果高分化胃癌组10例(20%),灌注参数：BF 值(mL·min-1·100 g-1)75.28±6.81,BV 值(mL/100 g)9.01±0.94,MTT 值(s)9.89±1.65,PS 值(mL·min-1·100 g-1)10.05±0.71;中分化胃癌组24例(48%),灌注参数：BF 值110.01±31.90,BV 值18.18±5.62,MTT 值9.81±3.69,PS 值40.08±15.82;低分化胃癌组16例(32%),灌注参数：BF 值138.59±38.09,BV 值21.08±4.11,MTT 值9.47±1.80,PS 值57.50±13.28。3组比较,BF、BV、PS 值在高分化与中分化组以及高分化与低分化组间差异有统计学意义(P <0.05),MTT 值在胃癌不同分化3组间差异无统计学意义(P >0.05)。结论CT 灌注参数 BF、BV、PS 值可以作为胃癌恶性程度的评估指标。     

肝硬化CT分级的64层螺旋CT灌注成像分析

目的 探讨肝硬化CT分级的临床价值.方法 对17例健康正常志愿者、54例肝硬化患者行CT灌注扫描,测量其血流量(BF)、血容量(BV)、肝动脉分数(HAF)、对比剂平均通过时间(MTT)、血管表面通透性(PS),对获得的相应灌注图进行肝硬化分级分析.结果 CT分级肝硬化程度越重,BF、BV越小,MTT、HAF、PS、肝动脉灌注量(HAP)越大.HAF、HAP在正常肝与轻、中、重度肝硬化之间有明显差异,HAF在中、重度肝硬化组明显增高.HAP在重度肝硬化组明显增高,PS、MTT在各组之间没有统计学意义.结论 通过肝脏的CT灌注研究,进一步证明了肝硬化CT分级确实与肝脏的灌注有一定关系,对临床肝硬化评估有一定价值.     

肝炎、肝纤维化和早期肝硬化阶段肝脏CT灌注实验动物的初步研究

目的探讨螺旋CT灌注成像对肝炎、肝纤维化和早期肝硬化诊断的应用价值。方法分别对二乙基亚硝胺诱导的14只肝炎、肝纤维化和早期肝硬化时期的Wistar雄性大鼠和14只正常对照组大鼠行单层动态螺旋CT肝脏灌注扫描,用肝脏灌注分析软件取得不同病变阶段肝实质的灌注参数,并与病理改变作对照研究和统计学分析。结果时间密度灌注曲线合乎数据分析要求。自实验组肝炎到早期肝硬化时期,正常对照组的肝动脉血流(hepaticarterialflow,HAF)呈轻度下降趋势,平均通过时间(meantransittime,MTT)以及肝血流量(bloodflow,BF)、肝血容积(bloodvolume,BV)都有升高趋势;实验组HAF呈升高趋势,肝炎期、肝纤维化期和早期肝硬化期的平均HAF值分别为(0.33±0.23)%、(0.55±0.13)%、(0.70±0.24)%;MTT呈明显延长,3个病变阶段分别为(6.60±2.39)s、(11.41±3.92)s、(15.02±5.21)s;BV和BF都有下降,从肝炎期的(18.05±3.27)ml·100g-1和(152.84±59.12)ml·100g-1·min-1降为肝硬化期的(9.51±3.61)ml·100g-1和(117.59±78.66)ml·100g-1·min-1。统计结果显示实验组在不同时期的HAF和MTT的差异均有统计学意义(P值均<0.05);肝炎和早期肝硬化、肝纤维化和早期肝硬化阶段各实验组间BV和BF的差异有统计学意义(P值均<0.05);肝炎和肝纤维化间差异无统计学意义。肝炎阶段相应灌注层面肝脏的病理改变主要为肝细胞肿大;肝纤维化和早期肝硬化阶段主要是窦隙毛细血管化、血管外Disse间隙胶原沉积。结论CT肝脏灌注扫描能反映肝炎、肝纤维化和早期肝硬化的一些血液动力学改变。动态的肝脏血流灌注参数改变应对临床的早期诊断、治疗和疗效观察有重要价值。     

五期增强CT扫描评估正常肝实质及肝硬化患者肝脏灌注特性的可行性研究

【摘要】目的：探究五期增强CT扫描灌注参数评估正常肝实质及肝硬化者肝脏灌注特性的可行性及准确性。方法：正常或肝单发血管瘤（直径<2cm）者16例及肝硬化患者10例纳入本研究,均行腹部CT平扫及五期增强检查,包括动脉早期、动脉期、门脉期流入期、门脉期及延迟期。另外回顾性收集12例正常或肝单发血管瘤（直径<2cm）者的肝脏灌注数据纳入本研究。经后处理获取肝脏灌注参数,包括肝动脉灌注量（HAP）、门静脉灌注量（PVP）、肝动脉灌注指数（HPI）、血流量（BF）和血容量（BV）。由2位观察者分别测量五期增强CT及常规CT灌注后处理获取的各肝脏灌注参数。记录以上各扫描方式的容积CT剂量指数（CTDIvol）值。采用组内相关系数（ICC）评估2位观察者测量结果的一致性,比较正常肝实质五期增强CT与常规CT灌注、正常肝实质与肝硬化患者五期增强CT所得各灌注参数的差异,并比较五期增强CT扫描与常规CT灌注扫描的CTDIvol值差异。结果：2位观察者测量各灌注参数结果的一致性均良好（ICC值为 0.818~0.996）。正常肝实质五期增强CT与常规CT灌注得到的HPI、HAP、PVP、BF值差异均无统计学意义（P值分别为0.475、0.219、0.073、0.108）,而两者BV差异有统计学意义（P＜0.001)。五期增强CT扫描得到的参数中,肝硬化组HPI、HAP较正常肝实质组升高,PVP较正常肝实质组减低,且差异均有统计学意义（P值分别为＜0.001、0.042、0.002）;而两组间BV、BF值差异均无统计学意义（P值分别为0.488、0.093）。平扫加五期增强CT扫描的CTDIvol为（53.78±13.67）mGy,常规CT灌注扫描的CTDIvol为45.45mGy,两者差异有统计学意义（P=0.005）;单期增强CT扫描的CTDIvol为（8.96±2.28）mGy,为常规CT灌注扫描的19.7%。结论：五期增强CT对正常肝实质灌注评估结果与常规灌注CT具有较好的一致性,有望应用于肝硬化患者肝脏灌注改变的评估。     

肝泡球蚴病边缘区域CT灌注成像与组织病理对照研究

目的:应用CT灌注技术观察肝泡球蚴病(HAE)的影像特征,并分析病灶边缘区域CT灌注参数与组织病理学指标的关系,探讨CT灌注在评价HAE边缘区域血流状态的应用价值.方法:28例HAE患者行肝脏CT灌注检查,获得病灶中心、病灶边缘区域及周围肝脏组织的各项灌注参数,包括血流量(BF)、血容量(BV)、平均通过时间(MTT)、毛细血管表面通透性(PS)、肝动脉灌流分数(HAF)、肝动脉灌流量(HAP)及门静脉灌流量(PVP);其中17例患者手术治疗,观察新鲜手术标本后取病灶边缘区域HE染色和免疫组化测定微血管密度(MVD),分析CT灌注各项参数与MVD的相关性.结果:28例中选取独立HAE病灶31个,测得病灶中心、病灶边缘区域及周围肝脏组织的各项灌注参数的均值之间的差异均有统计学意义(P＜0.05),其中病灶边缘区域组与周围肝脏组织组的BF、MTT、PS、HAP、PVP参数间差异有统计学意义(P＜0.05),BV、HAF参数间差异无统计学意义(P＞0.05);17例术后病灶边缘区域CT灌注参数BF、HAF、HAP与MVD呈正相关(P＜0.05).结论:HAE病灶与周围肝组织间存在边缘浸润带,该区域血流灌注高于病灶内部及周围肝脏组织,CT灌注成像可以反映这一区域的血流状态及病灶的浸润范围,具有较高的临床应用价值.     

CT灌注成像评价兔肝VX2移植瘤射频热凝术后残癌的实验研究

目的 探讨CT灌注成像在兔肝VX2肿瘤射频消融(RFA)后残癌诊断中的应用价值.方法 制备兔肝VX2肿瘤模型,在进行射频不完全消融治疗后第3、7、14、21天行CT灌注成像检查,然后处死模型兔,进行病理检查对照,进行统计学分析.结果 术后7d内各灌注参数无统计学差异(P均＞0.05).术后第14天时炎症反应带的血流量(BF)、表面通透性(PMB)的均值分别为(32.37±3.30) mL·min-1·100 g-1、(16.35±2.86)mL· min-1·100 g-1,残癌的对应参数均值分别为(60.77±8.25) mL·min-1·100 9-1、(33.13±6.29)mL· min-1·100 g-1,2组的BF比较有显著差异(t=9.31,P=0.01),PMB比较有显著差异(t=9.12,P=0.00);其他参数均值差异无统计学意义(P＞0.05).术后21d2组的BF、血容量(BV)、PMB、肝动脉灌注量(ALP)、肝动脉灌注指数(HPI)比较P＜0.05,统计学有差异.门脉灌注量(PVP)均值差异无统计学意义(P＞0.05).结论 CT灌注成像能为RFA术后提供有价值的血流动力学信息,有助于兔肝VX2肿瘤RFA治疗后残癌的早期诊断.     

Reproducibility of left ventricular volume determinations with use of a semi-automated system

Reliability of a computer-assisted system for determination of left ventricular volumes was judged by multiple measurements of rotation ellipsoids, cadaver hearts, and cineangiograms from patients. The volume measurements in cadaver hearts provided a volume correction factor necessary for reproducible results. Variation coefficient for intraobserver and interobserver variability did not exceed 2.3% when calculated using rotation ellipsoids and was highest at 12.0% for the end-systolic volumes derived from patient films. When appropriate calibration methods are employed, different observers can make reliable left ventricular volume measurements aided by such systems.     

Quantification of mitral regurgitation with MR phase-velocity mapping using a control volume method

Reliable diagnosis and quantification of mitral regurgitation are important for patient management and for optimizing the time for surgery. Previous methods have often provided suboptimal results. The aim of this in vitro study was to evaluate MR phase-velocity mapping in quantifying the mitral regurgitant volume (MRV) using a control volume (CV) method. A number of contiguous slices were acquired with all three velocity components measured. A CV was then selected, encompassing the regurgitant orifice. Mass conservation dictates that the net inflow into the CV should be equal to the regurgitant flow. Results showed that a CV, the boundary voxels of which excluded the region of flow acceleration and aliasing at the orifice, provided accurate measurements of the regurgitant flow. A smaller CV provided erroneous results because of flow acceleration and velocity aliasing close to the orifice. A large CV generally provided inaccurate results because of reduced velocity sensitivity far from the orifice. Aortic outflow, orifice shape, and valve geometry did not affect the accuracy of the CV measurements. The CV method is a promising approach to the problem of quantification of the MRV.     

Red cell volume response to exercise training: Association with aging

Red blood cell volume (RBCV) is a main determinant of cardiorespiratory fitness in healthy individuals. However, it remains controversial to what extent exercise training (ExT) enhances RBCV. Therefore, we sought to systematically review and determine the effect of ExT on RBCV in healthy individuals across all ages. We conducted a systematic search of MEDLINE, Scopus, and Web of Science, since their inceptions until February 2016 for articles assessing the effect of ExT interventions (not including hypoxic training) on blood volumes in healthy individuals. A meta‐analysis was performed to determine the mean difference (MD) in RBCV between post‐ and pre‐ExT measurements. Thirty studies were included after systematic review, comprising a total of 299 healthy individuals (mean age = 19–71 years, 271 males). Exercise training programs primarily consisted in lower limb endurance training interventions (mean duration = 15.2 weeks). After data pooling, RBCV was not increased following ExT (MD = 49 mL, 95% CI = ?11, 108; P = 0.11). In subgroup analyses, RBCV was increased after ExT in young and middle‐aged individuals (mean age <60 year) (n = 106, MD = 81 mL, 95% CI = 0, 162; P < 0.05) but not in older study participants (mean age ≥60 year) (n = 110, MD = 13 mL, 95% CI = ?76, 102; P = 0.77). Heterogeneity was not detected among studies in young and middle‐aged (I² = 0%) and older individuals (I² = 0%). In conclusion, RBCV is moderately, yet consistently, enhanced by ExT in young and middle‐aged but not in older healthy individuals. Therefore, RBCV adaptations to ExT appear to be age dependent.     

Stroke volume measurements with first-pass dynamic positron emission tomography: Comparison with cardiovascular magnetic resonance

Background  The assessment of forward stroke volume (SV) using dynamic, first-pass cardiac positron emission tomography (PET) was shown to be feasible in a limited number of studies with small numbers of subjects. The aim of this study was to compare first-pass derived SV with cardiovascular magnetic resonance imaging (CMR)-obtained values in a larger population of subjects. Methods and Results  Fifty-nine subjects with varying degrees of cardiac function were studied. Stroke volume was assessed using oxygen-15-labeled water (H₂ ¹⁵O) dynamic first-pass PET for both the right ventricle (RV) and left ventricle (LV), and compared with the findings of aorta velocity-encoded phase-contrast CMR. The PET-estimated SV was higher for the RV than for the LV (133±34 vs 116±31 mL, P<.01, ±SD), and both were higher compared with values obtained by CMR (81±20 mL, both P<.01,±SD). Although significant, the correlations between PET and CMR were moderate for both the RV (r=0.37, P<.01) and the LV (r=0.40, P<.01,±SD). Bland-Altman analysis revealed a progressive overestimation with increasing SV measured in either ventricle. Conclusions  First-pass dynamic H₂ ¹⁵O PET for the assessment of forward SV is feasible, although values are progressively overestimated with increasing SV, particularly when the RV is used, and correlations with aorta velocity-encoded phase-contrast CMR are moderate. These findings are probably protocol-dependent and warrant further study before the use of first-pass dynamic H₂ ¹⁵O PET in clinical or research settings can be advocated.     

4种复苏方法对呼吸骤停猪肺通气的影响观察

目的 观察胸外按压心肺复苏(C-CPR)、经膈肌下抬挤心肺复苏(D-CPR)、腹部按压心肺复苏(A-CPR)和腹部提压心肺复苏(L-CPR)4种复苏方法对呼吸骤停猪通气的影响.方法 健康家猪28只随机分为4组,经静脉推注琥珀胆碱建立猪呼吸骤停模型,于呼吸骤停即刻分别进行C-CPR、D-CPR、A-CPR和L-CPR.复苏2min后停止按压,给予呼吸机辅助呼吸直至实验猪恢复自主呼吸.测定并比较基础状态时和复苏时4种复苏方法产生的潮气量(VT),并计算分钟通气量(MV);比较各组心率(HR)和平均动脉压(MAP)水平及自主呼吸恢复时间.结果 基础状态下,4组间VT和MV之间差异无统计学意义(P＞0.05).复苏2min时的VT和MV,D-CPR组高于C-CPR组,A-CPR组高于D- CPR组,L-CPR组高于A-CPR组,差异均有统计学意义(P＜0.01).复苏2min时,L-CPR组HR恢复接近于基础值,A-CPR组HR维持在呼吸骤停即刻水平,C-CPR组和D-CPR组HR明显低于基础值(P＜0.01);复苏2min后给予机械通气,复苏5min时各组HR均接近基础值.结论 在呼吸骤停猪模型中,L-CPR较其他3种CPR法能产生更大的VT和MV.     

表面三维重建超声心动图测定狗左心腔及塑料容器容量的研究

目的：观察评价表面三维超声心动图重建系统对容量测定的准确性。材料和方法：采用表面三维重建系统及常用二维超声心动图方法，测定８个塑料容器及１０个狗左心室腔容量并与实测值进行比较。结果：各种超声心动图方法所测容量与实测值之间无显著差别，均为高度相关。对所用各种超声方法所测容量值进行方差分析，Ｐ＞０．０５。结论：表面三维超声心动图在容量测定的准确性方面与常用的二维超声心动图方法相近，其优点是操作简便、实用、可形象地显示被测物体的表面轮廓。     

Measurement of renal volumes with contrast-enhanced MRI

PURPOSE: To determine the accuracy of in vivo magnetic resonance imaging (MRI) measurement of total renal parenchymal volume and medullary fraction. MATERIALS and METHODS: Sixteen kidneys in eight pigs were imaged with a multiphasic contrast-enhanced fast three-dimensional sequence on a 1.5-T imager. Kidney segmentation, followed by a process of signal intensity thresholding for cortical and nephrographic phase datasets, allowed for MRI measurements of parenchymal volume and medullary fraction. Autopsy provided reference standards of renal volume, weight, and medullary fraction. RESULTS: An excellent correlation was found between MRI measurement of total renal parenchymal volume and autopsy volume (R2 = 0.86) and weight (R2 = 0.90). Medullary fraction (mean +/- SD) measured with MRI was 0.120 +/- 0.067, and with autopsy was 0.116 +/- 0.025 (t-test P = 0.84, F-test P = 0.001). CONCLUSION: MRI measurements of total renal volume are accurate. MRI measurements of medullary fraction show promise, but precision is limited when using a simple signal intensity thresholding algorithm.     

Hemolysis induced by an extreme mountain ultra‐marathon is not associated with a decrease in total red blood cell volume

Prolonged running is known to induce hemolysis. It has been suggested that hemolysis may lead to a significant loss of red blood cells; however, its actual impact on the erythrocyte pool is unknown. Here, we test the hypothesis that prolonged running with high hemolytic potential decreases total red blood cell volume (RCV). Hemolysis (n = 22) and RCV (n = 19) were quantified in ultra‐marathon runners before and after a 166‐km long mountain ultra‐endurance marathon (RUN) with 9500 m of altitude gain/loss. Assessment of total hemoglobin mass (Hb_mass) and RCV was performed using a carbon monoxide rebreathing technique. RUN induced a marked acute‐phase response and promoted hemolysis, as shown by a decrease in serum haptoglobin (P < 0.05). Elevated serum erythropoietin concentration and reticulocyte count after RUN were indicative of erythropoietic stimulation. Following RUN, runners experienced hemodilution, mediated by a large plasma volume expansion and associated with a large increase in plasma aldosterone. However, neither Hb_mass nor RCV were found to be altered after RUN. Our findings indicate that mechanical/physiological stress associated with RUN promotes hemolysis but this has no impact on total erythrocyte volume. We therefore suggest that exercise ‘anemia’ is entirely due to plasma volume expansion and not to a concomitant decrease in RCV.     

Correction of helical CT attenuation values with wide beam collimation: in vitro test with urinary calculi

RATIONALE AND OBJECTIVES: Urinary calculi are now commonly detected with helical computed tomography (CT), and it has been proposed that stone composition can be determined from CT attenuation values. However, typical scans are made with a beam collimation of 5 mm or more, resulting in volume averaging and reduction in accuracy of attenuation measurement. The authors tested a model for correction of errors in attenuation values, even at section widths larger than the width of the object. MATERIALS AND METHODS: Human urinary stones were scanned with helical CT at different beam collimation widths. A computer model was used to predict the effect of beam width and stone size on accuracy of measured attenuation. RESULTS: At 3-mm collimation, the model corrected the attenuation readings with an underestimation of 12% +/- 1 (compared with values at 1-mm collimation; 127 stones; diameters of 1.7-11.3 mm). With attenuation measured at 10-mm collimation, the model underestimated the true value by 34% +/- 3 (103 stones), with a significant negative correlation with stone diameter on magnitude of error (diameters of 3.0-11.3 mm). Correlation of data from patient scans with subsequent in vitro scanning of the same stones confirmed the validity of the model, but corrected in vivo scans consistently yielded lower values for the stones than in vitro. CONCLUSION: Volume averaging effects on attenuation in helical CT are predictable in vitro for urinary calculi--and presumably for other roughly spherical structures--as long as section width does not excessively exceed the diameter of the structure.