11/13/200611ENGG 167 MEDICAL IMAGINGNov. 13PET imagingReferences: The Essential Physics of Medical Imaging, Bushberg et al, 2nded.Chapters 19, 21, 22, 24.Physics and Radiobiology of Nuclear Medicine, G. B. Saha, 2nded. 2001.http://www.dhmc.org2Today1) Positron Emission Tomography 2) cyclotrons3) CT/PET4) Dosimetry in Nuclear Medicine5) Compartmental ModelingRead Chapter 22Mon. & Wed. after Thanksgiving break:Industry/Product Review11/13/200623Positron Emission Tomography (PET) ImagingRef: Bushberg4PET Imaging – limitations in spatial resolutionRef: Bushberg11/13/200635PET ImagesRef: http://gamma.wustl.edu/pt059te183.html31 year old woman, with a history of poorly differentiated squamous cell carcinoma of the cervix diagnosed nine months earlier, presents with left groin and back painMultiplanar cross sectional F-18 FDG PET images F-18 FDG PET anterior projection image. 6Interpretation of PET imagesAxial CT and PET Findings in a Patient with Non–Small-Cell Lung Cancer.The preoperative CT scan reveals no metastases in the liver (Panel A). The PET scan shows three hot spots in the liver (Panel B). http://www.aboutcancer.com/pet_liver_pieterman.htm11/13/200647PET – coincidence detection β++ e-annihilation∆t< 10 ns?ignorereadingsRecord eventto projection datasinogramnoyes8PET – resolution limitations •Positron range in tissue < 2 mm for 18F•Gamma rays are not ‘exactly’ collinear (i.e. at 180oapart), there is actually an angular spread near 0.3 degrees•Detector size and sensitivity11/13/200659Positron Emission Tomography (PET) ImagingWash U Radiology dept=Blank transmission scanNo-injection transmission scanPET Emissionscan10PET Imaging - development of the sinogramWash U Radiology deptActivity distributionSinogramView angleDistance (detector #)Data acquisition11/13/2006611PET Imaging – development of the sinogramWash U Radiology dept12PET Imaging – development of the sinogramWash U Radiology deptBCDASource objectsφxrSinogram P(xr, φ)FilteredBackprojection11/13/2006713PET radionuclidesRef: Bushberg18F in fluorodeoxyglucose (FDG) is used in approximately 85% of all PET imaging procedures14Cyclotron – increasing energy of charged particles through cycling spiral path, used to bombard heavy elements & create isotopesRef: Bushberg11/13/2006815Radionuclide Generation – comparison of methodsRef: Bushberg16PET images –18FDGRef: http://www.nucmed.buffalo.edu/nrlgy1.htm#fdg_normal_brainx31This is an 18-FDG brain metabolism study of a normal volunteer. 18-Flurodeoxyglucose (18-FDG) is a tracer composed of radioactive fluorine (18-F, half-life of 110 minutes) and a sugar (deoxyglucose). This sugar enters cells in the brain in a manner similar to the way normal glucose enters them, and glucose is the primary source of energy for these cells. However, once inside a cell, 18-FDG essentially becomes trapped and is not metabolized further. Since the brain does not store energy but must have glucose supplied essentially "on demand" by the blood, and 18-FDG is taken up at a rate related to normal glucose uptake, we can use the 18-FDG to measure how active various parts of the brain areby measuring how much of it is taken up when tracer amounts are injected. For this study the subject was injected with the 18-FDG tracer as they lay quietly in the PET camera. The tracer was taken up into the brain over a period of 40 minutes, and then a 20 minute scan showing the distribution of the tracer was taken. The resulting image is dark where there is no uptake (metabolism of glucose) and becomes brighter as there is more and more uptake (higher metabolic rates). (source: SUNY/VAMC)11/13/200691718F-deoxyglucose preparationRef: http://www.scgh.health.wa.gov.au/pet/cyclotron.htmlMuch of the process of FDG production is automated, however manual preparation of a number of separate components is required just prior to the production, because of a very short shelf-life of some of the mixed components. Once the individual components are prepared, typically in small glass containers, they are connected to FDG production apparatus to undergo a sequencial process of chemistry in a carefully controlled environment. FDGproduction requires a starting product that undergoes mixing, heating, gassing, evaporation and filtering. To ensure that the final product is sterile and pyrogen free, the production must take place in a “clean room” laboratory.The final product is subjected to quality control tests required for a conventional drug, which include simple visual inspections such as pH and color of the final product as well as more complicated tests to ensure that no residual chemicals remain in the final product. The final product of FDG is essentially a man-made sugar molecule with one 18F attached to each molecule.18PET images – H215ORef: http://www.nucmed.buffalo.edu/nrlgy1.htm#fdg_normal_brainx31An image of "15-O water" tracer distribution in a normal volunteer. Trace amounts of 15-O (half-life = 123 sec.) in the form of water are injected into the subject as a bolus. The 15-O water falls into the category of a "freely diffuseable" tracer which means it can readily cross cell boundaries to obtain a concentration in the cells on par with its concentration in the arterial blood. The 15-O water image shows activity in areas where there is blood flow (increased flow means you see more tracer). As mentioned in the 18-FDG Normal Brain discussion above, cells in the brain do not store energy -consequently it must be supplied essentially on demand. Since the energy (glucose) is brought to the cells by the blood, increased local energy demand necessitates increased local blood flow and hence increased 15-O water tracer uptake. Combining the data in this image with data indicating the amount of 15-O tracer available in the general arterial blood pool as a function of time (obtained by rapidly acquiring arterial blood samples while the images are being taken) allows us to convert the raw 15-O water tracer images into quantitative images of regional Cerebral Blood Flow (rCBF; see below). (source: SUNY/VAMC)11/13/20061019PET 18FDG images of tumor hypermetabolismRef: http://www.nucmed.buffalo.edu/nrlgy1.htm#fdg_normal_brainx31(source: SUNY/VAMC) Hypermetabolic tumor with 18-FDG uptake. Note the hypometabolism in the affected hemisphere.20Combined CT and PET systemsDedicated PET and Spiral CT technologiesHR+. The highest performance PET system in the world today. The HR+boasts the