Presented at the Sixth International Conference on Positron Annihilation, Ft.Worth, TX, April 3-7, 1982 and to be published in the Proceedings. Also presented at The Workshop on Positron Emission Tomography, Edmonton, Alberta, Canada, April 21-23, 1982 £5e w 3 z o 4 s 6 > ~ DYNAMIC POSITRON-EMISSION TOMOGRAPHY IN MAN USING SMALL BISMUTH GERMANATE CRYSTALS S.E. Derenzo, T.F. Budinger, R.H. Huesman, and J.L. Cahoon April 1982 Prepared for the U.S. Department of Energy under Contract DE-AC03-76SF00098 LEGAL NOTICE This book was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Govern­ ment nor any agency thereof, nor, any of their employees, makes any warranty, express or im­ plied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. 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' ' ' jjic Proceedings of the Sixth International represents that its use would not infringe pnvatelv owned rights e.erenc ■ commercial product, process, or service by trade name, t r a d e d , manufacturer, or othe^rw , j Conference on Positron Annihilation, nol necessarily constitute or imply its endorsement, recommendation or 1avor' ® * States Government or any agency thereof. The viev.* and opinions of aut ors e»or Fort Worth, Texas, April 3-7, 1982 necessarily state or reflect those of the United States Government or v agency thereof. North-Hoi land Publishing Company LBL— 14308 DYNAMIC POSITRON-EMISSION TOMOGRAPHY IN MAN USING SMALL BISMUTH GERMANATE CRYSTALS* DE82 014997 S.E. Derenzo, T.F. Budinger, R.H. Huesman, and J.L. Cahoon Lawrence Berkeley Laboratory and Oonner Laboratory University of California, Berkeley CA 94720, U.S.A. Primary considerations for the design of positron emission tomographs for medical studies in humans are the need for high imaging se n sitivity, whole organ coverage, good spatial resolution, high maximum data rates, adequate spatial sampling with mini­ mum mechanical motion, shielding against out of plane activity, pulse height discrim i­ nation against scattered photons, and timing discrimination against accidental coinci­ dences. We discuss the choice of detectors, sampling motion, shielding, and electron­ ics to meet these objectives. INTRODUCTION For the past 50 years, since the pioneering work TABLE 1. EXAMPLES OF POSITRON LABELED COMPOUNDS of Von Hevesy, the radioactive tracer technique AND THE PROCESSES THAT THEY MEASURE has been used with considerable success in the biological sciences to measure fundamental bio­ TRACER PROCESS MEASURED chemical processes in plants and animals. In this spirit Positron Emission Tomography (PET) Heart: is being vigorously developed because it appears to be the best high resolution technique for the ionic 82Rb muscle perfusion quantitative regional measurement of tracer com­ pounds in the human body after a simple n C palmitate fatty acid oxidation injection. 18F deoxyglucose tissue demand for glucose Table 1 lists a few of the positron labeled com­ pounds that have been recently developed and the U C or 13N amino muscle regeneration and biochemical processes upon which their biodis­ acids metabolism tribution depends. We believe that many more w ill be developed in the years to come so that Brain: v irtu a lly any metabolic process can be measured non-invasively. 150 blood flow and oxygen utilization 2j_ HISTORY OF PET INSTRUMENTATION 31C bioamines blood flow and receptor Historically, positron emission tomography for sites the three-dimensional imaging of positron labeled compounds in the human body has evolved ionic 82Rb blood brain barrier through five stages (Figure,1): breakdown [1] Limited angle tomography using pairs of 18F deoxyglucose tissue demand for glucose Anger scintillation cameras,1*8 parallel planes of scintillation crystals9' 13 or n C methionine blood brain barrier wire chambers with converters19* 25 (Figure transport la ). Full angular , coverage requires rotation. “ C, 13N, or 18F receptor sites psychoactive [2] A single circular array of closely packed compounds scintillation crystals.-26*'*1* To obtain mul­ tiple transverse sections axial translation is required. [3] Hexagonal or octagonal arrays of scintilla­ *This work was supported by the Office of Health tion crystals that are both translated and and Environmental Research of the U.S. Depart­ rotated for full linear, angular, and axial ment of Energy under Contract No. DE-AC03- coverage (Fig lc ) . I*5* 52 76SF00098 and also by the National Institutes of Health, National Heart, Lung, and Blood Insti­ [4] Multiple layers of configurations [2] and tute under grant No. P01 HL25840-02. [3] above (Figs Id and le ) . 53-63 have been more fully described in previous papers.77>78 [1] The highest possible dose efficiency, which requires both a large solid angle and high detection efficiency. Time-of-flight infor­ mation can su bstantially reduce the number of events needed for a given statistical accuracy (especially for large emission regions). [2] A resolution of 5 irm FWHM or better, capa­ ble of quantitative measurements of regions 10 mm in size. The requirement for dynamic, gated imaging means that th is resolution must be achieved with lit t le or no mechani­ cal sampling motion. [3] The ability to measure the arterial input function of the tracer to the organ being imaged and to follow its subsequent accumu­ lation and clearance. This requires the ability to collect sufficient data in typi­ c a lly 10 second time frames and permits very little sampling motion.77*79 [4] A sufficient number of transverse sections to cover the volume of interest which is usually more than 5 cm axially. [5] Discrimination against background events by shielding, and by timing and pulse height discrimination. [6] Ability to correct data for accidental and f) Multiple Arroys With prompt scatter backgrounds and for image Time-of-Flight IT.O.F.) distortions. X8L023-3079 [7] Ability to tilt at least 15°. [8] A patient port of at least 50 cm for body Figure 1: Evolution of detector geometries for imaging and 25 cm for head imaging. positron emission tomography. 4^ DESIGN CONSIDERATIONS [5] Multiple circular arrays of fast scintilla­ tion crystals coupled to moderately large Design considerations for positron emission tom­ high-speed photomultiplier tubes for local­ ographs have been previously described in some ization by differential time-of-flight d e t a il. 27» 1,7» 77»80-83 Primary differences among measurement (Fig I f ) . 6**-75 designs occur in the choice of detector mate­ r ia l, the depth of the shielding, and the sam­ Fundamental considerations in positron emission pling employed. tomography for medical imaging show the advan­ tages of high density scintillators over wire 4.1 Detector Materials chambers and converters in terms of detection efficiency, time resolution, sensitivity, and Table 2 lists the three detector materials used maximum useful event ra te s.76 Contemporary in positron tomographs, N al(T l), CsF, and b is­ designs and the trend for the near future are muth germanate (BGO). Nal(Tl) leads in photon focussed on the multilayer approaches (Figures yield and pulse height resolution, CsF leads in le and If ) which provide the highest dose e f f i­ speed, and BGO leads in detection efficiency. An ciency and useful event rates. "ideal detector" with the best properties of all three would be very useful. 3^ MEDICAL OBJECTIVES While solid state detectors have been suggested We summarize below the primary requirements for for positron emission tomography,8**-86 their the quantitative