靶向整合素αvβ3探针用于甲状腺乳头状癌显像的研究

目的 制备特异性整合素αvβ3探针[^18F]氟化铝-匹仑吉肽（^18F-Al-NOTA-PRGD2）,探讨其用于甲状腺乳头状癌（PTC） PET显像的可行性.方法 采用氟化铝新策略制备18F-Al-NOTA-PRGD2.取新鲜切除的人PTC肿瘤组织接种于裸鼠右腋下,制得荷人PTC裸鼠模型.再分别取人PTC标本及毗邻的正常组织、荷瘤裸鼠移植瘤行整合素αvβ3免疫组织化学染色.荷瘤裸鼠（n=5）尾静脉注射1.1 MBq ^18F-Al-NOTA-PRGD2后30、60和120 min分别行microPET显像,通过ROI技术计算肿瘤和主要脏器的放射性摄取值（％ ID/g）,并通过阻断实验验证其特异性.另取15只荷瘤裸鼠研究其注药后30、60及120 min生物分布,计算放射性摄取值（％ID/g）.用两样本t检验进行统计学处理.结果 成功制备^18F-Al-NOTA-PRGD2,标记率＞45％.免疫组织化学染色证实人PTC标本和裸鼠移植瘤组织整合素αvβ3染色均呈棕褐色阳性表达,人PTC毗邻正常组织不表达.荷瘤裸鼠注射^18 F-Al-NOTA-PRGD2后行microPET显像示,肿瘤清晰可见,且与周围组织对比度良好.注射后30、60、120 min肿瘤对显像剂的摄取值分别为（2.81±0.35）、（2.45±0.27）和（1.80±0.21） ％ID/g.PRGD2阻断后,注射^18F-Al-NOTA-PRGD2后60 min肿瘤对显像剂的摄取值降为（0.51±0.05） ％ID/g.荷瘤裸鼠生物分布实验示,注射显像剂后30、60、120 min肿瘤摄取值分别为（3.09±0.25）、（2.75±0.37）和（1.90±0.16） ％ID/g,与microPET显像基本一致（t=1.456、1.465和0.847,均P＞0.05）.^18F-Al-NOTA-PRGD2在血液和肌肉中清除快,注射后60 min肿瘤与血液和肌肉的摄取比值分别为6.15±0.45和7.86±0.56.结论 ^18F-Al-NOTA-PRGD2制备简单,放化纯高,可有效监测PTC中整合素αvβ3表达水平;其PET显像有望为研究PTC整合素αvβ3受体相关机制提供一种新方法.     

正电子肿瘤阳性显像剂^18F—AMT

^18F-AMT(^18F-α-methyl-tyrosine,^18F-α-甲基酪氨酸）是新研制的一种正电子肿瘤阳性显像剂。^18F-AMT的合成方法较简单，在肿瘤／非靶组织的比值高于^18F-FDG(^18F-氟代脱氧葡萄糖），特别是在脑肿瘤显像方面较^18F-FDG显示更大的优越性。     

18F标记氟乙基胆碱的合成与动物显像

目的研制PET肿瘤显像剂18F-氟乙基胆碱(FECh).方法制备了FECh和18F-FECh,进行了放化纯、稳定性分析及生物实验.结果产物结构通过1H NMR谱的确认,采用手动和半自动合成装置完成标记,合成过程简便,收率稳定,放化纯＞99%,稳定性好.18F-FECh的正常小鼠分布与文献报道的11C-choline相似,毒性较小;18F-FECh在荷瘤鼠的肿瘤部位有浓集.结论18F-FECh可以成为较好的肿瘤阳性显像剂.     

^18F-FLT PET显像原理及肿瘤显像研究进展

^18F-脱氧葡萄糖（FDG）PET显像被广泛应用于肿瘤的诊断与分期,但这种显像技术仍有不足之处,其诊断肿瘤的灵敏度高,特异性低,常受到生理性摄取、炎性反应、结节病等良性疾病的干扰,易出现假阳性,因此临床亟需一种肿瘤特异性更好的显像剂。无限制增殖是肿瘤细胞的特性,因而用正电子核素标记的核苷及其类似物成为一种极具潜力的肿瘤显像剂。     

18 F-胆碱类似物的制备及动物体内分布研究

目的 研究肿瘤显像剂^18F标记胆碱类似物2－^18F－氟乙基－二甲基－2－氧乙基铵盐（FECH）。方法 通过两步反应制备FECH。^18F^-与乙二醇二对甲苯磺酸酯发生亲核取代反应，生成2－^18F－氟代乙醇－2－对甲苯磺酸酯，后者与N，N－二甲基乙醇胺反应制成FECH。测定FECH放化纯度及其正常小鼠与荷瘤裸鼠体内生物分布。结果 FECH放射化学产率为25％，总放化合成时间为80min，放射化学纯度＞99％。FECH在小鼠体内血液清除快，肝、肾、膀胱和胰腺有高放射性摄取，脑、心肌、胃、肠道及骨骼放射性摄取较低。有较高的肿瘤／血液、肿瘤／脑、肿瘤／心脏、肿瘤／胃及肿瘤／肌肉放射性比值。结论 ^18F－FECH可望用于某些肿瘤的PET显像。     

PET代谢显像剂11C-乙酸盐在临床中的应用

^18F-氟脱氧葡萄糖（^18F-FDG）是一种最常用的肿瘤正电子显像剂，但对于炎性病变鉴别困难，易得出肿瘤假阳性诊断结果。PET代谢显像剂^11C-乙酸能够弥补。^18F-FDGPET的某些不足，已用于各类肿瘤的诊断及鉴别诊断，特别是在肝癌以及前列腺癌等的诊断及鉴别诊断方面明显优于^18F-FDGPET；基于^11C-乙酸盐的特性，也常被用于心肌血流和灌注显像。     

18F-FLT在肺癌模型小鼠体内的生物分布及PET显像研究

目的评价3’-脱氧-3＇-^18F-氟代胸苷（^18F-FLT）作为一种新的PET示踪剂在恶性肿瘤诊断中的作用。方法采用荷肺腺癌T739小鼠模型。实验组经尾静脉注入^18F-FLT后30、60、90、120min（每时间点8只小鼠）分别用井型探测仪测量^18F-FLT的生物分布，并行PET显像。对照组（n=8）小鼠在注入^18F-FLT后60min测量生物分布并行PET显像。结果^18F-FLT在肿瘤部位有相当高的放射性摄取，在肾脏和脾脏亦有很高的放射性，肿瘤对血、肌肉及肺的T／NT比值均大于2。应用^18F-FLT的肿瘤PET显像清晰。结论肺腺癌组织中^18F-FLT摄取高于正常组织，可通过PET清晰显像，为进一步的临床研究提供了依据。     

99Tcm标记抗人粒细胞单抗SZ-102在荷人胰腺癌裸鼠的显像研究

目的研究^99Tc^m标记抗人粒细胞单克隆抗体SZ-102在荷人胰腺癌裸鼠体内显像及生物分布。方法以2-亚氨基噻吩盐酸盐(2-IT)修饰SZ-102，^99Tc^m-葡庚糖酸钠(GH)配体交换法标记SZ-102，经裸鼠尾静脉注入^99Tc^m-SZ-102后4、8和24h分别测定荷瘤小鼠体内组织的放射性分布，并于1和4h对裸鼠进行γ显像。结果γ显像及生物分布示，^99Tc^m-SZ-102静脉注入荷瘤鼠后1h，肿瘤清晰显影，随时间延长，瘤体内放射性越来越浓，且瘤组织与非瘤组织的放射性比值(T／NT)也逐渐增高，各时相肿瘤每克组织百分注射剂量率(％ID／g)高于注射^99Tc^m-IgG的对照组。结论^99Tc^m-SZ-102具有活体内定位导向能力，显像时间短。     

^18C-胆碱和^18F—FDG在肿瘤PET中的比较

^18C—胆碱是最近研制的一种正电子肿瘤阳性显像剂，在肿瘤／非靶组织的比值高于^18F—FDG，特别在脑肿瘤和前列腺癌显像方面较^18F—FDG显示出优势。^18C—胆碱和^18F—FDG在脑肿瘤、肺癌、食道癌和前列腺癌的诊断方面各有优劣，两的摄取机理与显像方法也不同。除了^18C—胆碱，还有^18F—氟代胆碱(^18F-fluorocholine)，其临床价值有待更多的研究来证实。     

99Tcm-DTPA-DG的制备及其荷瘤裸鼠实验研究

目的进行99Tcm-DTPA-脱氧葡萄糖(DG)的化学合成、标记物制备、质量控制及药理研究.方法合成的DTPA-DG用氯化亚锡作还原剂,与99TcmO4-混合,在25℃以上室温放置30 min或沸水浴反应10nin,用一步法进行99Tcm标记.丙酮和质量分数0.9%生理盐水作展开剂,用纸层析法鉴定99Tcm-DTPA-DG的放化纯、标记稳定性;进行乳腺癌MCF-7裸鼠体内生物分布实验及显像研究.结果标记产物放化纯＞99%.99Tcm-DTPA-DG荷瘤裸鼠生物分布显示,肿瘤/血液比值1、2 h分别为1.29、3.13,肿瘤/肌肉比值1、2 h分别为2.63、5.01.荷瘤裸鼠99Tcm-DTPA-DG显像显示肿瘤组织.结论99Tcm-DTPA-DG可能成为肿瘤葡萄糖代谢显像剂.     

A Brief Evaluation of Tumor Imaging in Mice with 99mTc-glucarate Including a Comparison with 18F-FDG

Objective: Recently 99mTc-glucarate, a radiolabeled glucose analogue, has been considered as a SPECT alternative to 18F-FDG and PET for non-invasive detection of certain tumors. Thus far there have been few studies on 99mTcglucarate for tumor imaging and fewer, if any, studies comparing 99mTc-glucarate with 18F-FDG. As a preliminary indication of the properties of 99mTc-glucarate as a possible substitute for 18F-FDG in animal studies, we have imaged mice bearing xenografts of four tumor types with 99mTc-glucarate and have compared in two mice with one of these tumor types the 99mTc and 18F biodistributions. Methods: Two mice bearing SUM190 breast cancer xenografts received 1 mCi of 99mTc-glucarate and were imaged on a NanoSPECT/CT small animal camera. One day later, the same animals received 1 mCi of 18F-FDG and were imaged on a MosaicHP PET small animal camera. In addition, 0.5-1 mCi of 99mTc-glucarate only was administered to mice bearing xenografts induced by BxPC3 pancreatic cancer cells, HEK-293 renal cell carcinomas cells or HCT-116 colorectal tumor cells. NanoSPECT/CT acquisitions were performed in these mice to evaluate tumor accumulations. Results: In the SUM190 xenografted mice, the average tumor accumulation was 1.4 % (ID%/cm3) for 99mTc-glucarate and 2.1 % (ID%/cm3) for 18F-FDG. While slightly higher than 99mTc-glucarate, the tumor accumulation of 18F-FDG was accompanied by higher bone marrow and muscle accumulations at levels that could interfere with the tumor image depending upon location. The whole body clearance of 99mTc-glucarate was faster than that of 18F-FDG. Tumor accumulation of 99mTc-glucarate varied among tumor types but the tumors were readily visible in all images. Conclusion: In a direct comparison in the same two SUM190 tumored animals, SPECT images obtained with 99mTcglucarate compared favorably with PET images obtained with 18F-FDG. Tumor images with 99mTc-glucarate were also positive in three additional tumor mouse models. While further comparison studies are necessary, we conclude that 99mTcglucarate may be a more convenient and less expensive alternative to 18F-FDG for tumored mouse studies.     

乳腺癌放射性核素分子显像研究进展

随着新型特异性显像剂和成像设备的出现,乳腺癌分子成像技术得以快速发展。乳腺癌放射性核素分子成像技术主要包括单光子发射体层成像（ＳＰＥＣＴ）、正电子发射体层成像（ＰＥＴ）、ＰＥＴ／ＣＴ以及正电子发射乳腺成像（ＰＥＭ）。显像剂包括临床应用最广泛的正电子示踪剂１８Ｆ－氟代脱氧葡萄糖 （１８Ｆ－ＦＤＧ ）、用于研究肿瘤细胞增殖显像的５－１８Ｆ－氟尿嘧啶（５－ＦＵ）及３－脱氧－３－氟胸腺嘧啶（ＦＬＴ）、通过肿瘤氨基酸代谢显像的精氨酸－甘氨酸－天冬氨酸（ＲＧＤ）类,还包括受体类的靶向显像剂如雌激素受体相关的１６α－［１８Ｆ］－１７β－雌二醇（ＦＥＳ）、放射性标记的人表皮生长因子受体２（ＨＥＲ２）及表皮生长因子受体（ＥＧＦＲ）等。目前用于乳腺显像的ＰＥＭ技术对乳腺癌的早期诊断及疗效预测效果显著,就乳腺癌放射性核素分子成像技术的研究进展予以综述。     

Anesthesia condition for (18)F-FDG imaging of lung metastasis tumors using small animal PET

Small animal positron emission tomography (PET) with (18)F-FDG has been increasingly used for tumor imaging in the murine model. The aim of this study was to establish the anesthesia condition for imaging of lung metastasis tumor using small animal (18)F-FDG PET. METHODS: To determine the impact of anesthesia on (18)F-FDG distribution in normal mice, five groups were studied under the following conditions: no anesthesia, ketamine and xylazine (Ke/Xy), 0.5% isoflurane (Iso 0.5), 1% isoflurane (Iso 1) and 2% isoflurane (Iso 2). The ex vivo counting, standard uptake value (SUV) image and glucose SUV of (18)F-FDG in various tissues were evaluated. The (18)F-FDG images in the lung metastasis tumor model were obtained under no anesthesia, Ke/Xy and Iso 0.5, and registered with CT image to clarify the tumor region. RESULTS: Blood glucose concentration and muscle uptake of (18)F-FDG in the Ke/Xy group markedly increased more than in the other groups. The Iso 2 group increased (18)F-FDG uptake in heart compared with the other groups. The Iso 0.5 anesthesized group showed the lowest (18)F-FDG uptake in heart and chest wall. The small size of lung metastasis tumor (2 mm) was clearly visualized by (18)F-FDG image with the Iso 0.5 anesthesia. CONCLUSION: Small animal (18)F-FDG PET imaging with Iso 0.5 anesthesia was appropriate for the detection of lung metastasis tumor. To acquire (18)F-FDG PET images with small animal PET, the type and level of anesthetic should be carefully considered to be suitable for the visualization of target tissue in the experimental model.     

Profiling EGFR in Triple Negative Breast Tumor Using Affibody PET Imaging

Objective Triple negative breast cancer(TNBC) represents a group of refractory breast cancers with aggressive clinical manifestations as well as poor prognoses.Human epidermal growth factor receptor(EGFR) expression is strongly associated with TNBC progression and it may serve as a therapeutic target for TNBC.We aimed to evaluate EGFR affibody-based PET imaging to profile EGFR expression in small animal models.Methods 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid(DOTA) conjugated Ac-Cys-ZEGFR:1907 was chemically synthesized using solid phase peptide synthesizer and then radiolabeled with 64Cu.The in vitro cell uptake study was performed using SUM159 and MCF7 cells.The biodistribution and small animal PET imaging using 64Cu-DOTA-ZEGFR:1907 were further carried out with nude mice bearing subcutaneous MDA-MB-231 and SUM159 tumors.Results DOTA-Ac-Cys-ZEGFR:1907 was successfully synthesized and radiolabeled with 64Cu.Biodistribution study showed that tumor uptake value of 64Cu-DOTA-Ac-Cys-ZEGFR:1907 remained at(4.07±0.93)％ID/g at 24 h in nude mice(n=4) bearing SUM159 xenografts.Furthermore,small animal PET imaging study clearly showed that 64Cu-DOTA-Ac-Cys-ZEGFR:1907 specifically delineated the EGFR positive TNBC tumors at 4 h or later.Conclusion The study demonstrates that 64Cu-DOTA-Ac-Cys-ZEGFR:1907 is a promising molecular probe for PET imaging of EGFR positive TNBC.EGFR based small protein scaffold holds great promise as a novel platform that can be used for EGFR profiling of TNBC.     

喉癌18F-FDG PET/CT显像的临床应用价值

目的探讨18F-脱氧葡萄糖(FDG)PET/CT显像相对于单独的18F-FDG PET显像在喉癌诊断中的临床价值以及评价平均标准化摄取值(SUVmean)在喉癌和喉生理性显像鉴别中的作用。方法疑似喉癌患者23例。男19例,女4例,年龄30～70岁。空腹6H以上,静脉注射7.4MBq/kg 18F-FDG后40min后仰卧位行头颈部或全身扫描。分别评价18F-FDG PET和18F-FDG PET/CT显像对病灶诊断的灵敏度和特异性。19例病理为鳞癌的喉癌患者与15例喉生理性显像患者作为对照,测定显像部位的SUVmean,试用受试者工作曲线特征(Receivrer Operation Characteristic,ROC)及阳性似然比(positive likelihood ratio,+LR)确定SUVmean阈值。结果 23例喉癌患者,108处病灶。18 F-FDGPET显像和18F-FDG PET/CT显像对病灶诊断的灵敏度分别为85.1%(40/47)和89.4%(42/47),差异无统计学意义(P>0.05),特异性分别为和72.1%(44/61)和91.8%(56/61),差异有统计学意义(P<0.05)。19例病理为鳞癌的喉癌患者SUVmean均数为7.3±2.9,15例喉生理性显像SUVmean均数为4.9±1.1,差异有统计学意义(P<0.05)。SU-Vmean阈值选定为6.1,18 F-FDG PET/CT显像喉癌诊断的灵敏性为63.2%,特异性为86.7%。结论 18 F-FDG PET/CT显像明显改善18F-FDG PET显像的特异性。SUVmean阈值选定为6.1,有利于喉癌和喉生理性显像的鉴别。     

Molecular imaging of brain tumors with 18F-DOPA PET and PET/CT

The objective of this study was to give an overview of the potential clinical utility of [18F]-L-dihydroxyphenylalanine (18F-DOPA) PET and PET/CT for imaging of brain tumors. Review articles and reference lists were used to supplement the search findings. 18F-DOPA has been investigated as a PET tracer for primary brain tumors, metastases of somatic cancer, and evaluation of relapse of pathology in patients with brain tumor after surgery and/or radiotherapy on the basis of enhanced cell proliferation. Available studies have provided encouraging preliminary results for diagnosis of brain tumors and relapse after surgery/radiotherapy. In the brain, excellent discrimination between tumor and normal tissue can be achieved because of the low physiological uptake of 18F-DOPA and the high ratio between tumor and normal hemispheric tissue. Information on evaluation of brain metastases is limited but encouraging. PET and PET/CT with 18F-DOPA are useful in diagnosing primary brain tumors and should be recommended in the diagnosis of relapse of disease after surgical treatment and/or radiotherapy. Semiquantitative analysis could improve diagnosis while correlative imaging with MRI is essential. Limits are due to low knowledge of potential pitfalls.     

18F-FDOPA PET imaging of brain tumors: comparison study with 18F-FDG PET and evaluation of diagnostic accuracy.

We evaluated the amino acid and glucose metabolism of brain tumors by using PET with 3,4-dihydroxy-6-(18)F-fluoro-l-phenylalanine ((18)F-FDOPA) and (18)F-FDG. METHODS: Eighty-one patients undergoing evaluation for brain tumors were studied. Initially, 30 patients underwent PET with (18)F-FDOPA and (18)F-FDG within the same week. Tracer kinetics in normal brain and tumor tissues were estimated. PET uptake was quantified by use of standardized uptake values and the ratio of tumor uptake to normal hemispheric tissue uptake (T/N). In addition, PET uptake with (18)F-FDOPA was quantified by use of ratios of tumor uptake to striatum uptake (T/S) and of tumor uptake to white matter uptake. The accuracies of (18)F-FDOPA and (18)F-FDG PET were determined by comparing imaging data with histologic findings and findings of clinical follow-up of up to 31 mo (mean, 20 mo). To further validate the accuracy of (18)F-FDOPA PET, (18)F-FDOPA PET was performed with an additional 51 patients undergoing brain tumor evaluation. RESULTS: Tracer uptake in tumors on (18)F-FDOPA scans was rapid, peaking at approximately 15 min after intravenous injection. Tumor uptake could be distinguished from that of the striatum by the difference in peak times. Both high-grade and low-grade tumors were well visualized with (18)F-FDOPA. The sensitivity for identifying tumors was substantially higher with (18)F-FDOPA PET than with (18)F-FDG PET at comparable specificities, as determined by simple visual inspection, especially for the assessment of low-grade tumors. Using receiver-operating-characteristic curve analysis, we found the optimal threshold for (18)F-FDOPA to be a T/S of greater than 1.0 (sensitivity, 96%; specificity, 100%) or a T/N of greater than 1.3 (sensitivity, 96%; specificity, 86%). The high diagnostic accuracy of (18)F-FDOPA PET at these thresholds was confirmed with the additional 51 patients (a total of 81 patients: sensitivity, 98%; specificity, 86%; positive predictive value, 95%; negative predictive value, 95%). No significant difference in tumor uptake on (18)F-FDOPA scans was seen between low-grade and high-grade tumors (P = 0.40) or between contrast-enhancing and nonenhancing tumors (P = 0.97). Radiation necrosis was generally distinguishable from tumors on (18)F-FDOPA scans (P < 0.00001). CONCLUSION: (18)F-FDOPA PET was more accurate than (18)F-FDG PET for imaging of low-grade tumors and evaluating recurrent tumors. (18)F-FDOPA PET may prove especially useful for imaging of recurrent low-grade tumors and for distinguishing tumor recurrence from radiation necrosis.     

F-18 fluorodeoxyglucose positron-emission tomography in the diagnosis of tumor recurrence and metastases in the follow-up of patients with breast carcinoma: a comparison to conventional imaging

AIM: To evaluate the role of F-18-fluorodeoxyglucose positron-emission tomography (F-18 FDG PET) in the follow-up of breast carcinoma in case of clinical suspicion of local recurrence or distant metastases and/or tumor marker increase in correlation to conventional imaging. MATERIAL AND METHODS: Retrospective analysis of the results of F-18 FDG PET (ECAT ART(R), Siemens CTI MS) of 62 patients (age 58.5 +/- 12.8) with surgically resected breast carcinoma (time interval after surgery, 86 +/- 82 months, mean follow-up 24 +/- 12.6 months). Patient- and lesion-based comparison with conventional imaging (CI) including mammography (MG), ultrasonography (US), computerized tomography (CT), magnetic resonance imaging (MRI), radiography (XR) and bone scintigraphy (BS). Furthermore, we evaluated the influence on tumor stage and therapeutic strategy. A visual qualitative evaluation of lesions was performed. RESULTS: On a patient base, sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy for detecting local recurrence or distant metastases were calculated to be 97%, 82%, 87%, 96% and 90% compared with 84%, 60%, 73%, 75% and 74% with CI. On a lesion base, significantly more lymph node (84 vs. 23, P < 0.05) and fewer bone metastases (61 vs. 97, P < 0.05) could be detected by using F-18 FDG PET compared with CI. Sclerotic bone lesions were predominantly detected by BS. On the other hand, there were several patients with more FDG positive bone lesions and also mixed FDG positive/Tc-99m methylenediphosphonate (MDP) negative and FDG negative/Tc-99m MDP positive metastases. In case of normal tumor markers, sensitivity, specificity, PPV, NPV and accuracy for detecting local recurrence or distant metastases were calculated to be 100%, 85.0%, 78.6%, 100% and 90.3% for FDG PET and 80%, 50%, 50%, 80% and 61.5% for CI. An upstaging could be observed in 9.7% (6/62) and downstaging in 12.9% (8/62), leading to a change in therapeutic regimen in 13 patients (21%). CONCLUSIONS: F-18 FDG PET demonstrates apparent advantages in the diagnosis of metastases in patients with breast carcinoma, compared with conventional imaging on a patient base. On a lesion base, significantly more lymph node and less bone metastases can be detected by using F-18 FDG PET compared with conventional imaging, including bone scintigraphy. In patients with clinical suspicion but negative tumor marker profile, too, F-18 FDG PET seems to be a reliable imaging tool for detection of tumor recurrence or metastases. Considering the high predictive value of F-18 FDG PET, tumor stage and therapeutic strategy will be reconsidered in several patients.     

Alginate moulding: an empirical method for magnetic resonance imaging/positron emission tomography co-registration in a tumor rat model

BACKGROUND AND PURPOSE: In the experimental field of animal models, co-registration between positron emission tomography (PET) and magnetic resonance imaging (MRI) data still relies on non-automated post-processing using sophisticated algorithms and software developments. We assessed the value of an empirical method using alginate moulding for PET-MR co-registration in a tumor rat model. METHODS: Male WAG/RijHsd rats bearing grafted syngenic rhabdomyosarcoma were examined under general anesthesia by MRI using a clinical whole-body 3-T system equipped with a sensitivity-encoding four-channel wrist coil and by a small animal PET system using labelled [(18)F]-fluorocholine as tracer. An alginate mould including a system of external fiducials was manufactured for each animal, allowing strict immobilization and similar positioning for both modalities. Fourteen rats (27 tumors) had only one MR/PET imaging session. Five rats (9 tumors) had a similar MR/PET session before and 3 days after external radiation therapy (13 Gy in one fraction) using the same mould. Co-registration was performed using the Pmod release 2.75 software (PMOD Technologies, Ltd., Adliswil, Switzerland) with mutual information algorithm. RESULTS: The manufacture of the alginate moulds was easy and innocuous. Imaging sessions were well tolerated. PET-MR co-registration based on mutual information was perfect at visual examination, which was confirmed by the superimposition of external fiducials on fused images. Reuse of the same mould for the post-therapeutic session was feasible 3 days after the pre-therapeutic one in spite of tumor growth. CONCLUSION: The empirical method using alginate moulding with external fiducials for PET-MR co-registration in a rodent tumor model was feasible and accurate.