PET CT Imaging and Fusion Technology

PET/CT Imaging and Fusion Technology ACMP June 14th 2004 Phil Vernon PET/CT Research Manager GE Healthcare Why PET/CT ? Why PET ? “Conventional” Imaging - Shows only major structural changes - Relatively poor at finding neoplasia - Very poor at characterizing tissue - Slow at showing metabolic change in response to therapy FDG PET Imaging - “Lights Up” cancer - Demonstrates metabolic change in Rx GE Proprietary and Confidential Why PET/CT ? Why PET/CT ? But PET Imaging - Shows limited anatomy - Has poor spatial resolution - Takes a long time (relative to CT/X-ray) - Is not widely understood by physicians & surgeons PET/CT Imaging - Adds anatomy to the PET scan - Reduces Imaging time - Improves acceptability by referring physicians GE Proprietary and Confidential SENSITIVITY AND SPECIFICITY OF PET AND CT IN CANCERS Sensitivity (Detect cancer?) Specificity (Detect only cancer?) PET Lung Diagnosis Staging Recurrence 98% 82% 98% CT 67% 61% 72% PET 73% 91% 92% CT 76% 95% Change in Patient Management Due to PET 37% Colorectal Recurrence 93% 89% 83% 84% 77% 80% 85% 93% 95% 91% 68% 73% 31% 21% 10% 26% Lymphoma Staging Recurrence Melanoma Staging 88% 75% GE Proprietary and Confidential Classification Correct TUMOR STAGE CT alone Classification Correct but Equivocal 8 (20%) 16 (40%) Classification Incorrect 23 (58%) 16 (40%) 9 (22%) 8 (20%) PET alone Visual Correlation26 (65%) 5 (12%) 9 (22%) of PET and CT Integrated PET/CT 35 (88%) 4 (10%) 1 ( 2%) NODE STAGE CT alone 22 (59%) 2 ( 5%) 13 (35%) PET alone Visual Correlation of PET and CT Integrated PET/CT 18 (49%) 22 (59%) 30 (81%) 14 (38%) 4 (11%) 1 ( 3%) 5 (14%) 11 (30%) 6 (16%) Lardinois,D et al. Staging of Non-small-cell Lung Cancer with Intergrate PET/CT and CT. N Engl J Med 328:25 2003 GE Proprietary and Confidential “ . . .integrated PET-CT is superior to PET alone, CT alone, or visual correlation of PET and CT in determining the stage of disease in nonsmall-cell lung cancer.” “Since PET images have a fairly high resolution, lesions that are less than 1 cm can be detected. This is a critical advantage over conventional CT and magnetic resonance imaging” “However tracing focal abnormalities to specific lymph nodes is difficult, or even impossible with the use of PET alone.” “Several studies has demonstrated that fusion of images of the trunk obtained by CT and PET from different scanners is technically possible. 2628 However, this approach did not increase the accuracy of mediastinal staging over that obtained by PET alone.” Lardinois,D et al. Staging of Non-small-cell Lung Cancer with Intergrate PET/CT and CT. N Engl J Med 328:25 2003 26. Wahl,R et al. Staging of mediastinal non-small-cell lung cancer with FDG PET, CT and Fustion Images. Radiology 1994; 191:371-377 27. Vansteenkiste JF, et al. FDG-PET in potentially operable non-small cell lung cancer: do Fusion images improve the localisation of regional lymph node metastases? Eur J Nucl Med 1998; 25:1495-1501. 28. Magnani P, Carretta A, Rizzo G et al. FDG PET and spiral CT image fusion for mediastinal lymph node assessment of non-small cell lung cancer patients J Cardiovasc Surg 1999; 40:741-8 GE Proprietary and Confidential If PET/CT is Good What is the best technology ? What is it good for ? GE Proprietary and Confidential If PET/CT is Good What is the best technology ? How important are Resolution, Sensitivity, Scatter Fraction, Countrate Performance? (Physical Performance defined by NEMA standards) What about Crystal Technology ? Do we need 64-slice CT ? What really matters ? GE Proprietary and Confidential If PET/CT is Good What is PET/CT Good for ? Staging (we have lots of good references) What about - Screening for Cancer ? - Cardiology ? - Neurology ? - Radiation Treatment Planning ? - Evaluating Cancer Treatment ? Where does PET/CT give the greatest clinical advantage ? GE Proprietary and Confidential What is the best technology ? How important are Resolution, Sensitivity, Scatter Fraction, Countrate Performance? (Physical Performance defined by NEMA standards for PET) Resolution - How big does a 1 mm source appear to be. Limits ability to see edges. Impacts ability to detect, and define the shape of, small objects. Sensitivity - How much information is collected per unit time from a given quantity of tracer. Primary determinant of signal-tonoise level. Principal limitation on ability to locate small foci. Scatter Fraction - What fraction of the data collected is scatter (ba data). Degrades signal-to-noise. Count Rate Performance – As the tracer dose is increased, how much more information is collected. GE Proprietary and Confidential What is the best technology ? Resolution - Average resolution 5.5mm to 7.5mm FWHM Newer systems have poorer resolution than older designs Sensitivity - Varies from about 3.5 to 9.2 cps/kBq without septa (3D) Very large variation from one design to another Scatter Fraction – From about 37% to 50% without septa (3D), 16% with septa (2D) Count Rate Performance – Most meaningful measurement is a graph of NECR vs tracer concentration. NECR (Noise Equivalent) Countrate) is total countrate corrected for scatter and random events (both are noise), but also penalized for the noise added by NEMA NU2, 2001 (based on whole-body phantom) the correction. (NU2 1994 -based on brain phantom - will appear on some following slides because 2001 numbers are not available from all vendors) GE Proprietary and Confidential Spatial Resolution: Reveal Hi-Rez1 Spatial Resolution @ 1 cm @ 10 cm @ 20 cm 4.6 5.8 6.8 6.3 5.7 7.4 8.6 6.1 7.4 6.9 7.6 Reveal Discovery Discovery Gemini5 RT2 ST3 LS4 6.9 4.8 5.1 6.2 5.4 4.9 5.5 5.6 ? NEMA Resolution is NOT but is “How small an object can I see?” “How big does a 1 mm object appear?” 1 – CTI Brochures distributed at RSNA 2 – Reilly Commnunications (www.reillycomm.com)2004 3 – Mawlawi, O, et al. JNM June 2003, and in press 4 – DeGrado, JNM 35, 8 1994 5 – Reilly Commnunications (www.reillycomm.com)2004 GE Proprietary and Confidential Sensitivity Amount of Information per milliCurie of Tracer Injected 3D Sensitivity 1994 kcps/uCi/ml 2001 cps/kBq 2D Sensitivity 1994 kcps/uCi/ml 2001 cps/kBq Discovery ST [BGO] Discovery LS [BGO] Mfg A LSO 1280 1060 780 9.1 6.5 ? 300 220 2.1 1.3 Mfg A Mfg B LSO GSO 800 660 4.5 ? GE Proprietary and Confidential Scatter Fraction Percentage of collected data that is Invalid (noise due to scatter) 3D SF Nema 1994 2D SF Nema 1994 Discovery LS Discovery ST Mfg A Mfg A LSO LSO 30 % 29 35 30 10 % 16 Mfg B GSO 30 Scatter from a 20 cm x 20 cm phantom GE Proprietary and Confidential NECR kcps 100000 Discovery ST DST 2D Practical Clinical Range for Onocolgy 80000 60000 40000 DST 3D Mawlawi et al (J Nuc Med, June 2003 and in press) 20000 0 10 GE Proprietary and Confidential 70Kg patient (154 lb) 15mCi injection 45 min uptake 10 20 30 40 50 60 70 kBq/cc 80 20 30 40 50 60 70 80 mCi at time of scan NECR kcps 100000 NECR Curves (Noise Equivalent Count Rate) DST 2D Mawlawi et al (J Nuc Med, June 2003 and in press) Practical Clinical Range for Onocolgy 80000 60000 NECR = T2 T+S+2R T2 T+S+R NECR = 40000 DST 3D 70Kg patient (154 lb) 15mCi injection 45 min uptake 10 20 30 40 20000 NECR = 92kcps @ 49 kBq/cc 0 10 GE Proprietary and Confidential kBq/cc 50 60 70 80 20 30 40 50 60 70 80 mCi at time of scan COUNTS Determine Image Quality Noise in PET images is dominated by the counting statistics of the coincidence events detected. Noise in images can be reduced by filtering, but at the cost of resolution. 105 106 107 counts Unapodized ramp filter Hanning window, 4mm Hanning window, 8mm GE Proprietary and Confidential What is the Best way to Acquire Data ? GE Proprietary and Confidential 2D Acquisition All events used to reconstruct a slice are detected within that slice. GE Proprietary and Confidential 2D Acquisition Events that cross several slices are rejected. GE Proprietary and Confidential 3D Acquisition Events which cross several transaxial slices are collected. These events are used in the reconstruction of each of the slices crossed. GE Proprietary and Confidential But the world is full Randoms and Scatter. GE Proprietary and Confidential But the world is full Randoms and Scatter. Both Scatter and Randoms can be significantly reduced by Septa. GE Proprietary and Confidential But Septa also remove those rays that Cross several slices, and are in used in 3D imaging. SEPTA can only be used in 2D imaging GE Proprietary and Confidential 3D Compared to 2D SENSITIVITY RESOLUTION SCATTER FRACTION RANDOMS FRACTION 3D Better (more events) No Difference 3D Worse (no septa) 3D Worse (no septa) COUNTING RATE GE Proprietary and Confidential 3D Worse (more randoms & scatter) Patient #5 2D "Courtesy of The University of Texas, M.D. Anderson Cancer Center, PET Facility, Division of Diagnostic Imaging" Weight - 50 kg 110 lb BMI - 20.0 Activity at Acq Start 11.0 mCi 3 min/ FOV; 6 FOVs GE Proprietary and Confidential Patient #5 3D "Courtesy of The University of Texas, M.D. Anderson Cancer Center, PET Facility, Division of Diagnostic Imaging" Weight - 50 kg 110 lb BMI - 20.0 Activity at Acq Start 9.7 mCi 3 min/ FOV; 6 FOVs GE Proprietary and Confidential What about Crystals ? The primary detector is a scintillation crystal. It must stop the 511 keV gamma rays and convert the energy to light. The light is detected by photomultiplier tubes. PMT GE Proprietary and Confidential 3X 7X 25% GE Proprietary and Confidential Sensitivity DST BGO  20 mm OEM 1 LSO 11% of photons escape OEM 2 GSO 24% of photons escape 7% of photons escape 30 mm 93% of photons stopped 20 mm 89% of photons stopped 76% of photons stopped 30mm of BGO stops 93% of incident photons 25mm of LSO stops 88% of incident photons 20mm of GSO stops 76% of incident photons Rel Sensitivity ~ = 1.00 Rel Sensitivity ~= 0.79 Rel Sensitivity ~= 0.67 30mm of BGO provides the highest sensitivity GE Proprietary and Confidential Detector Scintillator Materials – Theory “Bench” Performance of Single Crystals in Ideal Conditions GSO BGO LSO Rel. Light Output 35% 22% 75% 75-80% More Light means we can: improve energy resolution (reduce scatter) connect more crystals/PMT (cut cost) Decay Constant (ns) 60 300 40 40 Short (Fast) means we can: reduce the number of randoms accept a higher count rate per crystal m(cm-1) Photo fraction High stopping power and photo fraction means: GE Proprietary and Confidential 0.67 0.95 ~28% ~40% .85 ~35% 0.80 ~35% higher sensitivity (more counts) Theory and Practice of PET Scanners “In theory, there is no difference between theory and practice; but in practice, there is.” Yogi Berra GE Proprietary and Confidential Detector Scintillator Materials – Practice Performance of Clinical Scanners – Engineering Design GSO1 Rel. Light Output 35% Energy ResolutionA 16% Scatter FractionB 30% Decay Constant (ns) Random Rate (rel) Peak NECRC (kcps) 65 66% 48 BGO2 22% 17% 29% 300 100% 62 LSO3 75% 25% 35% 40 50% 58 LYSO 75-80% 16% 30% 40 m(cm-1) 0.67 Photo fraction ~25% SensitivityD (kcps/uCi/ml) 700 0.95 ~40% 1280 .85 ~35% 780 .80 ~35% ~1100 Not All Scintillators Deliver on Their Promise 1 – Philips Allegro 2 – GE Discovery ST 3 – Siemens Biograph LSO GE Proprietary and Confidential A – Manufacturers specifications – www.reillycomm.com B – NEMA NU2 - 1994 from www.reillycomm.com C – NEMA NU2 - 2001 from Mfrs data sheets D – NEMA MU2 - 1994 from www.reillycomm.com With and Without Septa for 60 kg (130 lb) Patient Mayo Clinic - Abdomen/Liver FDG Geometry Crystal Depth Final Image No Septa – 3D 15mCi (555 MBq), scanned 1hour 18 min post injection 8.7mCi at Acq. time 523 K counts/sec Crystal Depth = 30mm Trues = 126K Random= 314K Scatter = 83K Trues = 24% R+S = 76% LSO/PICO ~ 63 ~ 100 ~ 70 NECR 17 NECR = 30.4 kcps Septa - 2D 15mCi injected, scanned 51 min post injection 10mCi at Acq. time 50 K counts/sec Crystal Depth = 30mm Trues = 39.3K Random= 4.7K Scatter= 6.0K Trues = 79% R+S = 21% NECR = 30.9 kcps GE Proprietary and Confidential 1895: “The first Car uses new Piston Engine” GE Proprietary and Confidential 1954 - “Gas Turbine Engine Replaces Piston Engine in Cars” "[By 1965] the deluxe open-road car will probably be 20 feet long, and powered by a gas turbine engine” -Leo Cherne, 1955. GE Proprietary and Confidential 1979 - “Wankel Rotary Engine Replaces Piston Engine in Cars” 1979 1986 "The Wankel [engine] will. . .dwarf such major post-war technological developments as xerography, the Polaroid camera and color television." -General Motors, 1969. 1993 GE Proprietary and Confidential 2004 - Piston Engine Replaces “new” competitors in 99.99%* of All Cars * .01% = sum of Electric, hybrid, and Rotary GE Proprietary and Confidential Forget the Headlines ! It’s not about the Crystals 1979 1986 1903 Do you buy a car by the engine name* ? . . . . or by performance and capability ? * Did you know the Hemi isn’t a hemi ? GE Proprietary and Confidential What about CT ? How Much CT do I need in a PET/CT ? Largely doing whole-body Imaging, so the CT must be reasonably fast (but the PET takes 20 min!) Thin slices useful if doing RT planning, or if using CT CAD to map lung nodules Multi-Slice important for gating (heart and respiration). GE Proprietary and Confidential Thin Slices Drive DRR Quality 3mm slices 1.2mm slices GE Proprietary and Confidential 2D, 3D -> 4D Imaging 4D provides: Respiratory gating Provides more precise tumor contouring for Radiation Therapy Planning GE Proprietary and Confidential Our PET is growing up GE Proprietary and Confidential