مجله پزشکی هسته ای ایران
سال:1386 | دوره:15 | شماره:2 (28) |تعداد مقالات:11

The advent of dual-modality PET/CT imaging has revolutionized the practice of clinical oncology, cardiology and neurology by improving lesions localization and the possibility of accurate quantitative analysis. In addition, the use of CT images for CT-based attenuation correction (CTAC) allows to decrease the overall scanning time and to create a noise-free attenuation map (mmap). The near simultaneous data acquisition in a fixed combination of a PET and a CT scanner in a hybrid PET/CT imaging system with a common patent table minimizes spatial and temporal mismatches between the modalities by elimination the need to move the patient in between exams. As PET/CT technology becomes more widely available, studies are beginning to appear in the literature that document the use of PET/CT in a variety of different cancers, including lung, thyroid, ovarian, lymphoma, and unknown primary cancers, and for general oncology, cardiology and neurology applications. Specific applications of PET/CT, such as those for radiation therapy planning, are also being explored. The purpose of this review paper is to introduce the principles of PET/CT imaging systems and describe the sources of error and artifact in CT-based attenuation correction algorithm. This paper also focuses on recent developments and future trends in hybrid imaging and their areas of application. It should be noted that due to limited space, the references contained herein are for illustrative purposes and are not inclusive; no implication that those chosen are better than others not mentioned is intended.

Transient ischemic left ventricular dilation (TID) is a marker of severe and extensive coronary artery disease as well as an increased risk of adverse outcomes. The patients with more severe and extensive ischemia, multivessel-type of perfusion abnormality as well as patients with left anterior descending artery (LAD) territory perfusion abnormality have more probability of having TID. Evaluation of TID may be purely visual, or based on calculation of TID ratio between stress and rest images. Cutoff values for an abnormal TID ratio vary widely throughout the literature and may be related to different factors like patient populations and imaging protocols. On the other hand, several other causes of TID in the absence of significant epicardial stenoses have been reported. These include severe hypertension with myocardial hypertrophy; hypertrophic cardiomyopathy; and dilated cardiomyopathy.

Introduction: Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract. GIST has been shown to over-express c-KIT (CD117), the receptor tyrosine kinase. Imatinib (STI571 or Glivec) is a new type of tyrosine kinase inhibitor that selectively inhibits various tyrosine kinases and has been successfully used to treat GIST. In this study we have compared the results of F-18 FDG PET with those of CT in patients with GIST before and early after the treatment with Imatinib. Methods: The performance of CT and FDG PET imaging in the staging and follow-up of GIST lesion was retrospectively evaluated and compared in 15 patients with 67 suspicious lesions. All patients were examined before and after treatment with Imatinib. Findings of CT and FDG PET were compared on both patient- and lesion-based basis for the whole group and for anatomic locations.Results: Overall 67 lesions were detected in both pre-therapeutic FDG PET and CT imaging. In the pre-treatment studies there was no significant difference between detected lesions on FDG PET and CT (p=0.19). However, after treatment with Imatinib (follow-up interval of 30±16 days), FDG PET predicted response to therapy earlier than CT in 18% of lesions and 14% of patients, respectively. There was no significant difference in the density of malignant lesions by means of Hounsfield unit (HU) in the baseline PET in comparison to the early post-therapeutic investigations (93±16 vs. 90±22).Conclusion: For treatment monitoring of Imatinib in GIST patients, FDG PET gives more precise information of active state of disease compared with CT.

Introduction: This report describes the synthesis of 2-Amino-2-deoxy(S-benzoylthioacetyl)-D-glucose (S-Bz-TADG), radiolabeled with [99mTc(CO)3(OH2)3]+ complex with a procedure including deprotection of the benzoyl group, characterization by HPLC using a C18 reverse phase column and preliminary biodistribution study in normal mice.Methods: [99mTc(CO)3(H2O)3]+ complex was used to label TA-DG with 99mTc. This complex was prepared using up to 46 mCi of Na99mTcO4 in 1mL saline. The radiochemical purity (>95%) was determined by TLC in normal saline solution as the mobile phase. Radio-HPLC analysis of [99mTc]-(TA-DG) at pH=9.5-10, revealed that labeling with 99mTc resulted in the formation of three radiochemical species (Na99mTcO4 with tR=5.7 min, [99mTc (CO)3 (H2O)3]+ complex with tR=27.5 min and [99mTc]-(TA-DG) [yield >85%] with tR=8.2 min) with different HPLC-profiles.Results: The biodistribution of the [99mTc]-(TA-DG) complex was studied in normal mice (body mass 25–35 g) at 30 min and 1 h post-injection, according to a published procedure. This complex showed negligible brain uptake (0.13%±0.03 ID) at 30 min post-injection, an efficient clearance from the blood, a rapid excretion to the urine and a low retention in the liver and kidneys.Conclusion: Nonfunctionalized carbohydrate compounds such as glucose are generally weak ligands for chelating with 99mTc. Therefore, functionalization with an external chelating group or the insertion of some functional groups is essential to obtain strong metal-binding compounds. On the basis of our results, it seems that [99mTc]-(TA-DG) has not most of the favorable properties as an imaging agent for brain tumors.

Introduction: There are several technical features that make PET an ideal device for the noninvasive evaluation of cardiac physiology. Organ motion due to respiration is a major challenge in diagnostic imaging, especially in cardiac PET imaging. These motions reduce image quality by spreading the radiotracer activity over an increased volume, distorting apparent lesion size and shape and reducing both signal and signal-to-noise ratio levels.Methods: 4D average male torso (2 cm diaphragmatic motion) produced by NCAT phantom was used for simulations. Emission sinograms generated by Eidolon PET simulator were reconstructed using iterative algorithm using STIR. The respiratory motion correction (RMC) applied to data sets using an automatic algorithm. Cross section views, activity profiles, contrast-to-noise ratios and left ventricle myocardium widths of corrected and noncorrected images were compared to investigate the effect of applied correction. Results: Comparison of respiratory motion corrected and non corrected images showed that the algorithm properly restores the left ventricle myocardium width, activity profile and improves contrast-to-noise ratios in all cases. Comparing the contrast recovery coefficient (Qm)shows that the applied correction effected phases of number 7,8 and 9 of cardiac cycle more than the other 13 phases and the maximum value being 1.43±0.07 for phase number 8. The maximum value of ratio of the left ventricle myocardium width for non-RMC and RMC images along the line profile passing the apicobasal direction and along the line profile passing from the middle of the lateral wall of the left ventricle were 1.38±0.07 for phase number 9 and 1.12±0.03 for phases of number 8 and 9 respectively. Conclusion: Blurring and ghosting of each image depends on the speed of diaphragm during that respiratory phase. This simulation study demonstrates that respiratory motion correction has good overall effect on PET cardiac images and can reduces errors originating from diaphragmatic motion and deformation. Effect of such a correction varies from one cardiac phase to another and this depends on the blurring and ghosting of all respiratory phases used to form this cardiac phase. Using an automatic algorithm capable of correcting respiratory motion using full signal may be very useful to prevent lengthening of the overall scan time to obtain same motionless lesion signal levels.