多种损伤因子与重型颅脑损伤凝血功能障碍的相关性研究

目的 探讨内毒素（LPS）、白细胞介素-6（IL-6）、磷脂酶A2（PLA2）、血小板活化因子（PAF）与重型颅脑损伤凝血功能障碍的相关性.方法 收集我院急诊科符合重型颅脑损伤诊断标准的患者65例作为观察组,急诊抢救的同时检测其血小板计数（PLT）、部分活化凝血酶原时间（APTT）、凝血酶原时间（PT）、血浆D-二聚体（D-D）、LPS、IL-6、PLA2、PAF;以同期健康体检者43例作为对照组,对两组检测结果进行统计学分析.结果 两组比较,观察组PLT减少（t=3.892,P＜0.01）,APTT、PT、D-D、LPS、IL-6、PLA2、PAF均升高（t=3.971、3.904、6.532、4.028、4.115、4.274、5.037,P＜0.01）;观察组PLT与LPS、IL-6、PLA2、PAF之间相关系数（r）均≤-0.9319,呈显著负相关;APTT、PT、D-D与LPS、IL-6、PLA2、PAF之间r值均≥0.9091,呈显著正相关.结论 LPS、IL-6、PLA2、PAF参与了重型颅脑损伤凝血功能障碍的发生过程,对LPS、IL-6、PLA2、PAF进行早期干预,可减轻患者凝血功能障碍.     

舰(潜)艇高血压患者血压与儿茶酚胺水平关系的探讨

目的:研究舰(潜)艇原发性高血压(EH)患者偶测血压(CBP)及动态血压(ABP)与血浆肾上腺素(E)、去甲肾上腺素(NE)水平的关系.方法:监测EH患者的CBP和ABP,用放免法测定血浆E和NE浓度.结果:EH患者(n=36)血浆E、NE水平明显高于对照组(n=26)(P均<0.01);随着高血压分级的增加,升高更明显(P<0.01);潜艇组高于水面舰艇组(P<0.05);24h平均收缩压(SBP)、舒张压(DBP)及日间平均SBP、DBP与血浆E、NE水平呈正相关(r=0.338～0.498,P<0.01～0.001);偶测平均SBP与E、NE相关性次之(r=0.269～0.284,P<0.05);偶测平均DBP及夜间平均SBP、DBP与E、NE水平无相关性(r=0.198～0.231,P均>0.05).结论:交感神经活性亢进在舰(潜)艇育年军人高血压的发病机制中起重要作用;ABP与交感神经活性的相关性优于CBP.     

银杏苦内酯B对重症急性胰腺炎大鼠血浆TNFα的影响

 目的 观察重症急性胰腺炎(SAP)大鼠血浆中肿瘤坏死因子α(TNFα)的水平变化,探讨银杏苦内酯B(BN52021)对SAP的治疗作用.方法 选用Wistar大鼠45只,随机分成SAP模型组(SAP,n=15),BN52021治疗组(BN,n=15)和阴性对照组(NC,n=15).前两组以5%牛磺胆酸钠逆行注入主胰管制成SAP模型,制模15 min后,SAP组经股静脉以0.5 ml/100 mg注射生理盐水;BN组以BN52021(5 mg/kg)代替生理盐水静注;NC组仅做剖腹术.制模后1 h,6 h和12 h分别采血,应用ELISA技术测定血浆TNFα水平.结果 在1 h时相点,SAP组血浆TNFα水平(420.67±262.22 pg/ml)与BN组(403.88±177.92 pg/ml)、NC组(369.62±39.73 pg/ml)相比,均不具有显著性差异(P＞0.05);在6 h、12 h时相点,SAP组血浆TNFα水平(856.33±207.25 pg/ml,961.56±415.49 pg/ml)较NC组(369.14±16.28 pg/ml,416.43±26.54 pg/ml)明显升高(P＜0.05);BN组(415.15±88.08 pg/ml,692.06±69.31 pg/ml)较SAP组明显降低(P＜0.05).结论 实验证明SAP大鼠血浆TNFα水平明显升高,BN52021对SAP大鼠具有明显的治疗效果,使其血浆TNFα水平显著下降.     

PAF受体拮抗剂对内毒素血症幼年大鼠胃黏膜PGE2含量及COX-2表达的影响

目的探讨前列腺素E2(PGE2)、环氧化酶-2(COX-2)、血小板活化因子(PAF)受体拮抗剂在内毒素(LPS)腹腔注射诱导的幼年大鼠急性胃黏膜损伤中的作用。方法 18日龄Wistar大鼠192只,随机分为对照组、LPS组、PAF受体拮抗剂预防组和治疗组。采用LPS(O55:B5脂多糖)5mg/kg腹腔注射制备幼年大鼠LPS血症模型,预防组和治疗组分别于LPS腹腔注射前后0.5h应用5mg/kg PAF受体拮抗剂BN52021(Ginkgolide B),对照组腹腔注射等量生理盐水。于LPS注射后1.5、3、6、24、48、72h处死动物,每组每时间点8只,肉眼及光学显微镜下观察胃黏膜损伤情况,采用放射免疫法测定胃黏膜PGE2含量,免疫组织化学SP法测定胃黏膜COX-2蛋白的表达,半定量RT-PCR法测定胃黏膜COX-2 m RNA的表达。结果 LPS组腹腔注射LPS后1.5h黏膜上皮细胞水肿,3h组织充血、水肿,6h胃黏膜损伤最重,黏膜内有出血,细胞核碎裂、固缩,凋亡小体出现;24h上皮脱落、中性粒细胞浸润,48h黏膜层变薄、腺体减少,72h未见明显异常。预防组和治疗组改变轻微。与对照组比较,LPS组胃黏膜PGE2含量在3h时明显降低(P<0.05),6h时达最低(P<0.01),预防组胃黏膜PGE2含量在3、6h明显增高(P<0.05),治疗组PGE2含量在6h时明显增高(P<0.05)。与LPS组比较,预防组、治疗组胃黏膜PGE2含量在6h时均明显增高(P<0.01)。对照组胃黏膜组织未见明显COX-2蛋白及m RNA表达;与对照组比较,LPS组腹腔注射LPS后6h胃黏膜组织胞质即有COX-2蛋白表达,24、48、72h时明显增高(P<0.01),其m RNA水平亦上调;预防组和治疗组6h COX-2蛋白、m RNA水平明显增高(P<0.01);预防组和治疗组6h COX-2蛋白、24h COX-2 m RNA与LPS组比较亦明显增高(P<0.01)。结论 PAF受体拮抗剂可上调COX-2 m RNA及蛋白表达,使PGE2含量增加,对胃黏膜有保护作用。     

蜂毒肽MP-1对内毒素血症小鼠急性肺损伤保护作用的研究

目的探讨蜂毒肽MP-1对内毒素血症（ETM）小鼠急性肺损伤的保护作用。方法尾静脉注射内毒素（LPS）5mg/kg制备ETM小鼠模型。动物随机分为正常对照组（n=8）、ETM组（n=48）和MP-1治疗组（n=48,注射LPS的同时注射MP-1 3mg/kg）。ETM组和MP-1组分别于注射LPS后2、6、12、24、48、72h处死动物,采集血浆和肺组织标本,动态比浊法鲎试验检测各时相点血浆LPS水平,ELISA法检测血浆TNF-α和IL-6水平,real-ti me RT-PCR检测肺组织Toll样受体4（TLR4）、TNF-α和IL-6 mRNA表达,分光光度法检测肺组织髓过氧化物酶（MPO）活性,并观察伤后12h肺组织的病理变化。结果ETM小鼠伤后2-48h血浆LPS、TNF-α和IL-6水平显著增高（P〈0.01）,肺组织TLR4、TNF-α、IL-6 mRNA表达和MPO活性也明显增强（P〈0.05或P〈0.01）。MP-1治疗可不同程度降低血浆LPS和各细胞因子水平（P〈0.05或P〈0.01）,抑制肺组织相关基因表达及减低MPO活性（P〈0.05或P〈0.01）,并可减轻肺组织的病理损伤。结论MP-1可能通过中和LPS,减少LPS诱导的炎症介质的合成与释放,进而减轻炎症介质对肺组织的损伤。     

Anandamide-大麻素受体Ⅰ在内脏高敏感调控中的作用研究

目的研究Anandamide(ANA)-大麻受体Ⅰ(CB1)在内脏高敏感形成中的作用及其机制。方法采用鸡卵清蛋白(OVA)腹腔注射基础致敏,联合非伤害性/伤害性结直肠扩张刺激(NNCRD/NCRD),建立内脏高敏感性-NNCRD/NCRD大鼠模型。54只SD大鼠随机分为正常对照组(n=7),生理盐水+结直肠扩张(CRD)组(n=7),OVA+CRD+二甲亚枫(DMSO)组(n=8),OVA+CRD+不同剂量(0.5、5.0、10.0mg/kg)N-花生四烯酸氨基乙醇(ANA)组(n=8),OVA+CRD+ANA+AM251(选择性CB1受体拮抗剂)组(n=8)。采用免疫荧光组化及激光扫描共聚焦技术研究各组大鼠脊髓CB1阳性产物的分布特征及受体表达情况。根据腹壁肌电活动曲线下面积(AUC)评估内脏敏感性的变化。结果在80mmHg下行NCRD后,在L4-L6脊髓背角组织中,生理盐水+CRD组、OVA+CRD+DMSO组CB1受体表达明显增加(P<0.05);与生理盐水+CRD组比较,OVA+CRD+DMSO组CB1表达量明显增加(P<0.05)。在20mmHg压力下行NNCRD时,各组大鼠内脏运动反射(VMR)AUC比较差异无统计学意义(P>0.05)。在80mmHg压力下行NCRD时,生理盐水+CRD组VMR-AUC较OVA+CRD+DMSO组明显降低(P<0.05),OVA+CRD+ANA(高剂量)组VMR-AUC较OVA+CRD+DMSO组明显降低(P<0.05),而OVA+CRD+ANA+AM251组较OVA+CRD+ANA(高剂量)组VMR-AUC明显增加(P<0.05)。结论 ANA可缓解OVA基础致敏联合NCRD诱导的伤害性刺激作用,该作用是通过CB1受体介导的,提示ANA-CB1系统参与了内脏高敏感的调控过程。     

醒脑静注射液对兔内毒素休克的血液流变学影响

目的探讨醒脑静注射液对兔内毒素休克时血液流变学的改变及可能机制。方法日本大耳白兔18只,随机分为正常对照组、LPS组、LPS+XNJ组,每组各6只。用耳缘静脉推注LPS复制兔内毒素休克模型,再推注醒脑静注射液治疗。于0h、1h2、h、3h取血检测血液流变学指标。结果 LPS组与正常组比较,各时间点全血粘度(ηb)、血浆粘度(ηp)、血沉(ESR)、全血还原粘度(ηre)、红细胞聚集指数(EAI)、血沉方程K值(ESRK)均显著增高(P<0.05);LPS+XNJ组与LPS组比较,ηb、ηp、ESR、ηre均降低(P<0.05),且随时间延长其下降更加明显。结论醒脑静注射液能改善内毒素休克兔的血液流变性。     

曲古菌素A对脂多糖致急性肺损伤小鼠的保护作用观察

目的 探讨曲古菌素A(TSA)对脂多糖(LPS)所致急性肺损伤小鼠的保护作用及其机制.方法 健康雄性BALB/c小鼠60只,随机分为空白对照组、TSA组(灌胃给予TSA1mg/kg)、LPS组(气管内给予LPS1mg/kg)及TSA+LPS组(气管内给予LPS前1h灌胃给予TSA),每组15只.分别于处理后1、3、6、12、24h获取各组小鼠支气管肺泡灌洗液(BALF),采用ELISA法检测其中TNF-α和IL-1 β的浓度,并取肺组织测定肺干湿重比,HE染色后行病理组织学观察,ELISA法检测组织匀浆中髓过氧化物酶(MPO)活性及一氧化氮(NO)浓度.结果 与空白对照组及TSA组比较,LPS组小鼠肺组织可见明显的炎性细胞浸润等急性肺损伤病理学征象,肺组织湿干重比、MPO活性、NO浓度及BALF中TNF-α、IL-1 β浓度均明显升高(P＜0.05).与LPS组比较,TSA+LPS组上述改变均明显受抑,肺组织损伤减轻,组间比较差异有统计学意义(P＜0.05).结论 TSA对LPS诱导的急性肺损伤有保护作用,可能与其抑制了炎性细胞因子的生成有关.     

不稳定型心绞痛患者血浆蛋白标记物的蛋白质组学筛选

目的 分析冠心病不稳定型心绞痛(UAP)与稳定型心绞痛(SAP)患者血浆中的差异蛋白质,筛选可能与UAP早期诊断密切相关的血浆蛋白标记物.方法 分别收集2014年6月-2015年4月南方医科大学第三附属医院UAP及SAP血浆标本各60例,另收集体检科收集的血浆标本作为正常对照组(n=60).随机取对照组(n=10)、UAP组(n=10)与SAP组(n=10)空腹血浆标本各100μl,分别等量混合成3组样本,去除血浆高丰度蛋白后,利用双向差异凝胶电泳(DIGE)技术进行蛋白分离,经差异软件分析后,采集UAP和SAP之间变化2倍以上的差异蛋白质点,利用基质辅助激光解吸电离-飞行时间/飞行时间质谱(MALDI-TOF/TOF MS)对差异蛋白点进行鉴定.每组随机选取40份血浆样本,选取UAP特异性差异蛋白进行ELISA验证.结果 UAP与SAP组患者血浆相比较,共筛选出10个表达量差异2倍以上的差异蛋白点,包括9个上调蛋白点,1个下调蛋白点.经质谱鉴定后,表达上调的蛋白包括纤维蛋白原γ链(FGG)、补体C4-B(C4B)、免疫球蛋白κ链C结构域(IGKC)和血红蛋白α亚基(HBA1);表达下调的蛋白是结合珠蛋白(HP).与对照组比较后,在这些差异蛋白中共找到2个UAP特异性相关蛋白,即IGKC和HP.选取IGKC进行ELISA验证,结果表明,与对照组和SAP组相比较,UAP组样本中IGKC特异性表达上调(P<0.05),与DIGE验证结果一致.结论 筛选到UAP特异性相关蛋白IGKC和HP,IGKC有可能成为UAP早期筛查及诊断的特异性生物标记物.     

烧伤整形部位联合静脉麻醉对循环和应激的影响

目的研究部位联合静脉麻醉对烧伤后整形患者循环和应激的影响。方法40例择期成年整形患者,ASAⅠ~Ⅱ级,随机分成两组。对照组(A组,n=20)采取全凭静脉麻醉,静脉输0.2%异丙酚溶液2~8 mg/(kg.h)0、.1%氯胺酮溶液1~4 mg/(kg.h),间断静注氯胺酮注射液0.2~0.5 mg/kg、咪唑安定注射液0.02~0.05 mg/kg、芬太尼注射液1~1.5μg/kg;实验组(B组,n=20)静脉麻醉用药同A组,另外采用部位麻醉方法。两组在麻醉前后适时监测循环指标和皮质醇(Cort)、去甲肾上腺素(NE)、肾上腺素(E)浓度。结果两组切皮后30 min(T3)和切皮后1 h(T4)的平均动脉压、心率、Cort、NE、E等指标组间比较差异有统计学意义(P<0.05或P<0.01)。结论部位联合静脉麻醉用于成年烧伤整形患者,使其循环系统平稳,应激反应轻微,同时全麻用药量减小,术中、术后并发症少。     

Colonoscopy with computed tomography with volume reconstruction. The results and a comparison with endoscopy and surgery

PURPOSE: Virtual CT colonoscopy is a novel technique whose diagnostic accuracy and clinical yield are currently investigated. Several studies have shown its capabilities in detecting colon and rectal cancers. We report the results of a preliminary experience with the volume rendering technique and compare CT colonoscopy with endoscopy and surgery. MATERIAL AND METHODS: Our series consisted of 25 patients with colon cancer confirmed at endoscopy and/or surgery. All examinations were carried out with a spiral CT scanner Philips Tomoscan AVE1. Intestinal preparation was adequate in all patients, consisting in gas insufflated immediately before acquisition, after the injection of 100 mL iodinated contrast agent. All examination were performed in prone position using axial 5 mm slices with 5 mm table feed (pitch 1) and 2 mm reconstruction index; 120 kV and 200-250 mA were used. Images were transferred to a workstation (Easy Vision, Philips, release 4.2.1.1) for processing. We acquired multiplanar (MPR) and virtual endoscopic images with volume rendering; the selected threshold was -250 to -600 Hounsfield Units. Virtual endoscopic images could be obtained in 23 of 25 cases. The results of the radiological study were compared with endoscopic and surgical findings in 25 and 17 cases, respectively. RESULTS: Endoscopy and surgery detected 46 lesions: 29 were malignant and 17 benign. Axial CT and MPR alone detected 35 lesions (76%), 29 of them malignant and 6 benign. The 11 benign lesions missed by axial CT ranged 6-8 mm in diameter. There were no false positives. CT colonoscopy alone detected 66 lesions, but 22 of them were false positive due to residual stool in the colon (21 cases) and to residual barium in the colon (1 case). Combining CT colonoscopy and axial and MPR images enabled to correct the false positive diagnoses made by CT colonoscopy alone and to decrease the false negative ratio of axial and MPR images. Forty-one of 44 lesions (93%) were detected. Thirty-seven lesions were found in the 17 surgical patients; 34 of them were correctly identified combining CT colonoscopy and axial and MPR findings, while endoscopy detected only 31 lesions. Thus, CT had 92% sensitivity, versus 83% of fiberoptic endoscopy. CONCLUSION: In this preliminary experience volume rendering CT colonoscopy exhibited high sensitivity in detecting colon cancers, but their correct evaluation and characterization can be obtained if axial and MPR studies are combined. Further investigation and technological developments are necessary to define the yield of this new technique.     

Bronchogenic carcinoma: staging with MR compared with staging with CT and surgery

Thirty-three patients suspected of having bronchogenic carcinoma were studied prospectively using magnetic resonance (MR). In this group, 30 underwent examination with computed tomography (CT), 15 underwent thoracotomy, six had mediastinal biopsy procedures performed, and eight underwent bronchoscopy. MR studies, which included transaxial spin-echo imaging (TR, 0.5 and 2.0 sec; TE, 28 and 56 msec) of all patients and sagittal or coronal imaging of 18, were performed without knowledge of CT findings, using only plain radiographs as a guide. CT and MR studies were interpreted separately. CT and MR provided comparable information regarding the presence and size of mediastinal lymph nodes. MR better discriminated mediastinal nodes from vascular structures. However, in two of 11 patients who had multiple mediastinal lymph nodes that were normal in size at CT examination and surgery, MR suggested a confluent abnormal mass, probably because of its poorer spatial resolution. MR was superior to CT in showing enlarged hilar lymph nodes, but CT was better for demonstrating bronchial abnormalities. In three of four patients who had a proved hilar mass with distal obstructive pneumonia, MR (TR, 2.0 sec) helped distinguish between the mass and collapsed lung.     

Quantitative evaluation of muscle perfusion with CEUS and with MR

Functional imaging might increase the role of imaging in muscular diseases, since alterations of muscle morphology alone are not specific for a particular disease. Perfusion, i.e., the blood flow per tissue and time unit including capillary flow, is an important functional parameter. Pathological changes of skeletal muscle perfusion can be found in various clinical conditions, such as degenerative or inflammatory myopathies or peripheral arterial occlusive disease. This article reviews the theoretical basics of functional radiological techniques for assessing skeletal muscle perfusion and focuses on contrast-enhanced ultrasound (CEUS) and magnetic resonance imaging (MRI) techniques. Also, the applications of microvascular imaging, such as in detection of myositis and for discriminating myositis from other myopathies or evaluating peripheral arterial occlusive disease, are presented, and possible clinical indications are discussed. In conclusion, dedicated MR and CEUS methods are now available that visualize and quantify (patho-)physiologic information about microcirculation within skeletal muscles in vivo and hence establish a useful diagnostic tool for muscular diseases. Invited review article to European Radiology.     

Radiotherapy with and without temozolomide in elderly patients with glioblastoma

Background and purpose

The optimal treatment for elderly patients (age ???70?years) with glioblastoma (GBM) remains controversial. We conducted a retrospective analysis in 43 consecutive elderly patients with glioblastoma who either underwent radiotherapy (RT) or radiotherapy plus concomitant temozolomide (TMZ).

Patients and methods

A total of 43?patients (???70?years of age, median age 75.8?years) with newly diagnosed glioblastoma and a Karnofsky performance status (KPS) ???70 were treated with RT alone (median 60?Gy in 2?Gy single fractions) or RT plus TMZ at a dose of 75?mg/m² per day. The two groups were well-balanced; univariate (log-rank test) and multivariate Cox proportional hazards analysis were used to identify relevant prognostic factors.

Results

The median overall survival (mOS) of the entire patient cohort was 264?days (8.8?months) and the median progression-free survival (PFS) was 192?days (6.4?months). The factors age, sex, previous surgery, KPS, and concomitant use of TMZ had no significant influence on OS/PFS; multivariate analysis was performed to obtain adjusted hazard ratios. TMZ use resulted in a trend toward poorer overall survival when applied concomitantly (314?days compared to 192?days within the TMZ group, p?=?0.106). The subgroup analysis revealed that TMZ use resulted in significantly worse survival rates in patients with KPS70 (p?=?0.027), but for patients with KPS80 this difference was not detectable.

Conclusion

TMZ should only be used carefully in elderly patients with unfavorable KPS. In this patient cohort, radiotherapy alone is a reasonable option. Standard RT plus concomitant TMZ may be an advantageous treatment option for elderly patients with newly diagnosed glioblastoma who present with good prognostic factors.     

Intrahepatic arterioportal fistula and its treatment with detachable balloon and transcatheter embolization with coils and microspheres

BACKGROUND: Although intrahepatic arterioportal fistula (APF) due to acquired or congenital causes are infrequent, they are listed among the causes of portal hypertension. PURPOSE: The aim of this study was to present the results of intrahepatic APF treatment with embolotherapy in six cases. MATERIAL AND METHODS: Transarterial detachable balloon and coil embolization was used on six consecutive cases with traumatic intrahepatic APF from 1989 to 2003. Six-month follow-up angiography was obtained in every case. RESULTS: Successful disconnection of hepatic arterial and portal system was achieved in five cases. At least symptomatic improvement was achieved in one. CONCLUSION: Transcatheter embolization may be the first line of treatment for intrahepatic APF.     

肝癌经肝动脉栓塞术后癌灶化脓性感染的诊断和治疗

报道了７例肝癌经肝动脉栓塞术（ＴＡＥ）后合并感染、脓肿的病例。发生此一严重并发症的机率约为１．４％（７／４９５）。诊断主要依靠临床症状及ＣＴ、Ｂ超影像。在ＣＴ导向下的有效引流和对残癌组织用无水酒精冲洗则是最主要的治疗方法。其转归大概可分为：（１）脓肿痊愈、肿瘤姑息；（２）脓肿痊愈，活癌子灶仍存；（３）死于无法控制的感染。     

艾滋病合并肠管淋巴瘤X线、CT表现与病理

目的：探讨艾滋病合并肠管淋巴瘤的影像学特征表现与病理。方法：回顾性分析3例经活检及尸体解剖病理确诊的艾滋病合并肠管淋巴瘤患者的CT与病理资料。3例均经CT检查,其中2例经上消化道造影,1例钡剂灌肠造影。1例剖腹探查,切除部分增厚肠管组织病理证实,1例尸体解剖病理组织分析证实。结果：2例肠管淋巴瘤发生在空肠,1例发生在降结肠,影像与大体病理均表现为肠管壁不均匀增厚,管腔狭窄,充盈缺损,病理分型均为B细胞淋巴瘤。结论：艾滋病合并肠管B细胞淋巴瘤CT表现与病理符合度高。     

Suicide with moclobemide and perazine

A 51-year-old woman who was diagnosed as suffering from depression was found dead in her flat. The autopsy revealed no morphological changes sufficient to explain death. Toxicological analysis was performed and the drugs moclobemide (49.9 mg/l), perazine (1.27 mg/l) and some metabolites were identified in the blood. A combined drug intoxication resulting in synergistic effects to cardiovascular disorders was proposed as the cause of death. Received: 10 November 1997 / Received in revised form: 29 January 1998     

True tracers: comparing FDG with glucose and FLT with thymidine

As PET metabolic imaging becomes routine in clinical practice, there is a tendency to make imaging and data analysis fast and simple, but interpretation of these pictures by visual inspection does not do justice to the power of PET technology. Tissue data and blood data can be analyzed mathematically to provide parametric images of the PET tracer's biochemistry in terms of a transport parameter and a metabolic flux. The methods for parametric imaging with (11)C tracers of glucose and thymidine have been validated, but the short half-life of this radionuclide and the rapid metabolism of these labeled substrates to [(11)C]CO(2) have led investigators to develop (18)F analogs. While (18)F substitution at critical positions in the natural substrate can block metabolism, it has other effects on the transport and metabolism of the analog tracer. The fidelity with which analog tracers mimic tracers of the authentic substrate is critically evaluated for [(18)F]-2-fluoro-2-deoxyglucose and [(18)F]-3'-fluoro-3'-deoxythymidine.