Personal Notes of Robert E. Zimmerman from the Society of Nuclear Medicine Mid-Winter Meeting held in Las Vegas, 31 Jan - 3 Feb 1998: Updates on Tomography in Nuclear Medicine: Positron and SPECT The SNM mid-winter meeting is a generally low key affair with Councils and committees meeting on Saturday, Board of Delegates meeting on Sunday and a Scientific/Review meeting sponsored by the Computer and Instrumentation Council on Monday and Tuesday. Since NOBODY goes to Board meetings unless actually on the Board or severely politically inclined my personal agenda Sunday is to enjoy the local scene. That takes some advanced study when going to Vegas. We all know what the local scene in Las Vegas is. But I did not need adult fantasies. I wanted Las Vegas outdoors! I had to search rather intensively to get some clues as to where I might be able to hike or bike close to Vegas. The Internet is a wonderful place and it took several hours of searching but I was rewarded with several hits related to US government lands (the biggest landowner in Nevada) that were within an hour's drive or closer. Further research on the Internet turned up the email address of the president of the Las Vegas Valley Bicycle Club. She confirmed that Red Rock Canyon would be a bike ride within my capabilities. She tipped me off to a conveniently located bicycle rental and my recreational plans were set. Saturday, 31 January 1998 My Council obligation was with the Academic Council, who held their meeting on Sat afternoon. I have been involved with the teaching of nuclear medicine residents for my entire professional career. Never have I seen a future so apparently bleak. And it is not the quality of residents in nuclear medicine or their training that disappoints me. It is the fact that nuclear medicine residents seem to be a disappearing breed. Radiology and cardiology trained physicians seem to be taking an increasing number of "nuclear medicine jobs" and "our" profession suffers. Is the solution to become even more involved in the training and standards setting activities in these disciplines? Can these individuals master the intricacies of nuclear medicine? Where will the innovations and new applications come from? Clearly we are entering a new era in nuclear medicine in the US. There are opportunities for leadership here if some clear thinker can see the path through the enveloping thicket. Sunday 1 Feb 1998 All went according to plan and I had a great time bicycling to and around the Red Rock Canyon. Even time for a few short hikes. I returned tired and hungry to my hotel Sunday afternoon. Monday 2 Feb 1998 The main event, the reason for the long trip across the country: The Mid-Winter Symposium: Updates on Tomography in Nuclear Medicine: Positron and SPECT Organized by James Halama of Loyola U, Chicago with the assistance of Paul Christian of Salt Lake City, Utah. This was one of the best symposia of its kind I have been to in many years. All of the speakers, with few exceptions, were extremely well prepared and very informative. Over 100 attendees profited greatly from the talks and discussion that was generated. There was good interplay between academic researchers, clinicians and scientists from industry. It was truly an intelligence briefing for anyone interested in a snapshot of the current state-of-the art in the physics and instrumentation aspects of clinical tomography as it can be practiced today. This was all meat and no fluff. Lots to take home with you. Handouts, too. Physical Aspects of Positron Tomography Physical Characteristics of State-of-the-Art PET Systems Frederic H. Fahey, Wake Forest U School of Medicine, Winston- Salem, NC Fahey succinctly summarized the current instruments that are in general use and the machines that are currently available from Siemens-CTI, General Electric and Positron Corp. There was no mention of what MIGHT be available in the future, just a very cogent straight forward listing of the important specs on machines you can buy today. Physical Characteristics of 511 keV SPECT James A. Patton, Vanderbilt U, Nashville Dr. Patton has been making important contributions in this area together with the help of Elscint and ELGEMS for several years now. He shared with us some of this history, but more importantly he showed just what can be done with careful attention to details. Thicker crystals (5/8"), collimators designed for the specific imaging task (simultaneous MIBI perfusion and FDG cardiac imaging) have been successful at Vanderbilt. Spatial resolution and system sensitivity are sufficient to perform studies that answer clinical questions. He also told us what cannot be done. This technology was unsuccessful in brain imaging with FDG brain SPECT using special UHE fan beam collimators. Just could not get enough system resolution and sensitivity to perform adequately. Physical Characteristics of Gamma Camera Coincidence Imaging Gerd Muehllehner, UGM Inc., Philadelphia Dr. Muehllehner reviewed for us the technical advances that make it possible (and reasonable) to use NaI to detect annihilation quanta. A thick crystal, pulse shortening, local cluster position determination and multiple overlapping trigger channels are the keys. This is the technology first brought to the market in the PENN-PET or UGM machines (Quest-GE) and now in ADAC MCD dual-purpose PET- SPECT cameras. Picker and other companies also have or will have similar offerings. The most important parameter is the singles counting rate when using large area detectors. Singles counting rate of 1.5 Mcps leads to coincidence rates of about 13,000 cps. At some point the randoms will dominate. Clinical Experience with Positron Tomography Clinical Capabilities of State-of-the-Art PET David A. Mankoff, U Washington, Seattle Mankoff chose to concentrate on clinical tumor imaging. At U Washington this constitutes about 98% of clinical PET imaging. Indications for using PET are to distinguish benign vs. malignant, staging, response to therapy and tumor grading and prognosis. Attenuation correction is important. SUV, standardized uptake ratio, is calculated routinely to aid in interpretation. SUV of over 4 corresponds to tumor. Normal tissues are 2.5 and below. Detection of solitary lung nodule is approaching 100% sensitivity with specificity of over 80%. This gives credence to using PET for staging. Note these numbers apply to real PET, not collimated FDG imaging nor the PET/SPECT machines. The former has no hope at this task and the latter is marginal and at his time. All is not well with current PET machines, however. Attenuation correction takes too long. Resolution needs to be improved to 5-8 mm region and quantitative accuracy needs to be improved. Mankoff gathers hope from 3D acquisitions and new reconstruction methods which should provide better quantitation and detection. Clinical Capabilities of 511 keV SPECT Eric Q. Chen, Cleveland Clinic, Cleveland The use of collimated cameras for F-18 seems to have efficacy only for myocardial viability studies. For other applications the sensitivity and resolution do not seem to be sufficient. Camera Coincidence Imaging Robert E. Henkin, Loyal UMC, Chicago Henkin gave us the clinical perspective. He tried to answer the question of just where these new combination cameras can be used. Where are they efficacious? The complete answers are not in yet. But he has found utility in cardiac, brain and oncology applications. Cardiac scans need attenuation correction, which he now has on his ADAC. The brain scans look surprisingly good. There has been no head-to-head studies done with real PET. The study breakdown has been cardiac 30% and increasing, brain 20% and oncology 50%. Availability and Regulatory Issues of 18F-FDG: The Provider Perspective Ruth D. Tesar, PET Net Availability and Regulatory Issues of 18F-FDG: The User Perspective Edward Coleman, Duke U, Chapel Hill In this joint presentation we were reminded that the FDA currently has no authority over PET. This will probably change over the next four years but there seems to be some breathing room to pursue applications that may have otherwise been difficult. The breakdown at Duke for PET scans is roughly 5% myocardial viability, 30% WB oncology and 65% brain. PET/SPECT cameras have to be improved more before they can be considered ready for major contributions. Regional FDG distribution is happening and more areas are coming online each year. Panel Discussion: Clinical Positron Tomography - How & When? James R. Halama, Moderator; Frederic H. Fahey; James A. Patton; Gerd Muehllehner; David A. Mankoff; Eric Q. Chen; Robert E. Henkin This became a Q/A session with opportunity to fill in points that were not made by the speakers. It was emphasized that to make PET work there must be a full time, committed physician involved. Volume images will be an important way to digest the large amount of data presented for interpretation. There is a new journal coming out: Clinical Positron Imaging. Watch for it. Compensation & Data Corrections: Attenuation Correction in SPECT Overview of Attenuation Measurement and Correction Techniques in SPECT Michael A. King, U Mass, Worcester King reviewed the major issues surrounding SPECT attenuation correction and the various techniques that are in use or that have been proposed. A very complete look at the various methods. Overview of Scatter Correction Techniques in SPECT Eric C. Frey, U North Carolina, Chapel Hill The various techniques were reviewed and a nice outline in the handout summarized the talk nicely. Scatter correction is needed for quantitation and probably helps detection. The dual window scatter correction is pretty good and pretty easy but iterative methods will give superior results. More energy samples will have to help unless model-based methods prove more robust. Overview of Various Geometric Response Corrections in SPECT Larry Zeng, U Utah, Salt Lake City Zeng appeared to not be comfortable with analytical resolution corrections although he went to great lengths to explain them. If the speed problems can be overcome iterative reconstructions incorporating resolution and scatter corrections will prove superior. Attenuation Correction in SPECT Using Emission Data Alone Stephen C. Moore, Harvard Medical School, Boston Several investigators have succeed in getting the attenuator boundaries by using scatter windows, radioactive wraps on the patient surface and multiple radioactive tracers. It is also possible to perform attenuation correction knowing ONLY the projection data. It is somewhat counter intuitive, at first, that you might NOT need the attenuator map to do attenuation correction. But is can be shown that it is NOT needed if one applies consistency conditions to the projection data. Not ready for prime time yet, however. Tuesday 3 Feb 1998 The Clinical Case for Cardiac Imaging with Attenuation Correction: Has it Arrived? Robert C. Hendel, Northwestern U., Chicago Hendel thinks the key to seeing improvements due to attenuation corrections in cardiac SPECT will be in the normalcy rate. Improving the ability to call normals - normal. This was reported in a study by Ficaro about 18 months ago. Currently ADAC is sponsoring a 6 center trial of attenuation correction. Normalcy rate seen to be significantly improved WITH attenuation correction. Sensitivity unchanged. Specificity and accuracy also improved. It is necessary for readers to recalibrate and he feels that scatter correction and resolution recovery are must haves. Comparison of Current Vendor Offerings for Attenuation Correction in SPECT Tom R. Miller Washington U, St. Louis Miller gave another one of his superb summaries of what vendors are doing. This year pertaining to attenuation correction. Eight vendors were surveyed and the responses were cogently interpreted and presented. Lots of good information. Panel Discussion: Are We Ready for Quantitative SPECT? Paul E. Christian, Moderator; Michael A. King; Eric C. Frey; Larry Zeng; Stephen C. Moore; Robert C. Hendel; Tom R. Miller Some points made: Scatter correction helps the artifact due to liver activity. The best orbit depends on the number of heads. Three heads do 360, two heads do 180. Body contouring, scatter correction and resolution recovery were deemed necessary. For cardiac studies, it seems that pixel size should not exceed 6 mm. This calls for a roaming zoom (truncation?) or 128x128 matrix. Attenuation correction for thallium probably is best done sequentially since crossover corrections are so large. Some suggestions to manufacturers: We need attenuation correction for other parts of the body. Multicenter trials financed by companies are needed badly. Compensation & Data Corrections: Positron Tomography Randoms and Scatter in Gamma Camera Coincidence Imaging James DiFilippo, Picker First you have to minimize the detection of randoms and scatter by having a thick crystal, small coincidence time window and attention to geometry. Axial septa are known to help. Approximate corrections are sometimes used. Not quantitative, however. One gets the impression that there is more to do here as manufacturers come to terms with these big crystals. Most of the techniques known to be used in real PET are NOT used in gamma camera PET. Attenuation Correction in PET: Single Photon & Coincidence Transmission Measurements Joel S. Karp, U Pennsylvania, Philadelphia Joel Karp managed to bring the meeting to such fevered heights that the power failed during his discussion of attenuation correction in PET. Hotel electricians took about ten minutes to get the meeting back on track. Using Cs-137 results in faster and lower noise scans. Hybrid segmentation helps. 3D techniques offer advantages good energy resolution helps in attenuation correction. Attenuation correction is necessary. Attenuation Correction in gamma Camera Coincidence Imaging Horace H. Hines, Jr., ADAC, Milpitas ADAC uses slit collimated point sources of Cs-137. Data acquired after injection in a singles mode for 6 min. Rate is about 200-400kcps. Random and scatter corrections are coming. Final Comment: Great meeting in spite of the venue. Actually this hotel was one of the few with no bandits lurking at every turn. We hardly knew it was Vegas. A suggestion for future midwinter meetings: Include an icebreaker reception on Sunday or Monday evening to increase the opportunity to socialize and mingle with the diverse persons that come to this kind of meeting.