PET: New Technologies & Applications, Including Oncology, PhD, FIEEE Imaging Research Laboratory Department of Radiology University of Washington, Seattle, WA
Disclosures Research Contract, GE Healthcare Advisory Board, Aposense Inc.
Objectives 1. Review history and uses of PET/CT 2. Understand recent technology developments and challenges 3. Learn the context of the potential future applications of PET/CT imaging in clinical practice Outline Respiratory motion compensation Time of flight imaging Advanced modeling of PET physics in image reconstruction Extended axial field of view New detector systems PET/MR scanners CT dose reduction methods Cost effective PET/CT scanners
PET Technology Innovations 1953 First coincidence positron imaging system 1975 PETT III 1989 whole body imaging 1991 3D PET 1998 PET/CT 2005 2006 respiratory gating 2008 time offlight PET/MR? 2,500,000 2,000,000 Procedures/yr PET/CT % of Sales 100% 80% Procedures/yr 1,500,000 1,000,000 500,000 60% 40% 20% % scanners 0 0% 1998 2000 2002 2004 2006 2008
Respiratory motion compensation
Impact of Respiratory Motion Breath hold (BH) PET SUVs are 26% greater than free breathing (FB) PET SUVs Truth is not known Kawano, JNM 2008
Impact of Respiratory Motion Static wholebody Single respiratory phase (1 of 7, so noisier) 1 cc lesion on CT The SUV of the lesion goes from 2 in the static image to 6 in one phase of the respiratory gated image sequence
A Hierarchy of Respiratory Motion Compensation Methods 1. Breath hold PET 2. Cine+Helical CTAC 3. Respiratory gated PET (4D PET) 4. Phase matched 4D PET and 4D CTAC 5. Quiescent Period Gating 6. Respiratory Aligned and Summed Phases (RASP) 7. Internal External Correlation (INTEX) 8. Dual respiratory / cardiac gating 9. Reconstruction based methods Increasing complexity
Helical+CINE CTAC Acquisition to Compensating For Patient Motion 1. Standard non contrast helical CT (diagnostic beam) for both CT imaging correlation and for CTbased attenuation correction (CTAC) 2. Cine CT acquired over the diaphragm region for respiratory motion (much like a PET transmission scan: based on method of Pan et al. JNM 2005) 3. Average of helical+cine CT acquired is used for CTAC of PET data Sum of all CT scans used for CTAC
Helical+CINE CTAC Protocol upper limit of diaphragm motion Cine CT range lower limit of diaphragm motion max inspiration max expiration
Helical+CINE CTAC Protocol area of impact reduced 'banana' artifacts new cine+helical CTAC standard helical CTAC
Respiratory Gated PET/CT Imaging reflective block CT PET IR LEDs and camera Gating inputs PC w/ frame grabber + trigger generator Respiratory trace information
Wholebody Respiratory Gated PET Notes: motion throughout body changes in moving lesion intensity apparent fixed diaphragm location QuickTime and a YUV420 codec decompressor are needed to see this picture.
Single Phase CT based Attenuation Correction for 4D PET 1 X = Respiratory phases 2 3 X X = = N X = CTAC Phase Image Volumes PET EM phase sinograms Attenuation corrected PET data Reconstructed PET images
Phase matched CT based Attenuation Correction 1 X = Respiratory phases 2 3 X X = = N X = CTAC Phase Image Volumes PET EM phase sinograms Attenuation corrected PET data Reconstructed PET images
Single phase CT attenuation correction (CTAC) image (e.g. helical CT) Phasematched CTAC QuickTime and a decompressor are needed to see this picture. QuickTime and a decompressor are needed to see this picture. We see the time average of these images, unless we use respiratory gating
Phase matched 4D PET and 4D CTAC CT PET/CT 4D CT 4D PET/CT
Time of flight imaging
Time of Flight (TOF) PET/CT best guess about location (d) c = 3x10 10 cm/s, so t = 600 ps ~ d = 10 cm in resolution Surti (JNM 2011) shows improved lesion detection in large patients Little information yet on effect on impact on quantitative accuracy timing resolution uncertainty d = c t/2 + + e - annihilation
Impact of TOF PET Detection QuickTime and a decompressor are needed to see this picture.
Impact on quantitation Typical coincident count levels 75 kg patient, 120 MBq, 3 min/bed (BG = ~1kBq/cc) VOI & EANM MAX & EANM VOI & PSF+TOF MAX & PSF+TOF High coincident count levels 75 kg patient, 120 MBq, 10 min/bed (BG = ~1kBq/cc) VOI & EANM VOI & PSF+TOF MAX & EANM MAX & PSF+TOF 1.5 1.5 Recovery coefficient 1.25 1 0.75 0.5 Recovery coefficient 1.25 1 0.75 0.5 0.25 0.1 1 10 100 0.25 0.1 1 10 100 Sphere volume (ml) Sphere volume (ml) Courtesy Ronald Boellaard
Advanced modeling of PET physics in image reconstruction
Including improved physics modeling in image reconstruction In principle can remove detector blurring
Phantom measurements of ringing artifact QuickTime and a decompressor are needed to see this picture. real? QuickTime and a decompressor are needed to see this picture. QuickTime and a decompressor are needed to see this picture. Bai, 2010 IEEE MIC conf record
Extended axial field of view
Extended Axial Field of View PET scanner component has 3 rings of detector blocks. Siemens added one more ring (they quote "extra 33 %") to extend the axial field of view Increases scanner efficiency and/or allows for shorter scan times
NEMA NU 2 2001 performance measurements Noise Equivalent Count Rate Peak NECR (kcps) Biograph TP Peak NECR Biograph Biograph TP 96 @ 34 kbq/ml 161 @ 31 kbq/ml Biograph Courtesy David Townsend PhD: University of Tennessee at Knoxville
New detection systems Avalanche photodiodes Solid state silicon photomultipliers
Position sensitive avalanche photodiode (PSAPD) silicon based detectors Could ultimately be made cheaply in high volumes High optical quantum efficiency (up to 4x higher than PMTs) and wide spectral response Insensitivity to magnetic fields (used in PET/MR) Timing resolution of ~3 ns Lower SNR than PMTs Temperature sensitive gains Flood histogram from coupling a 8 x 8 mm 2 PSAPD to an LSO array (1 mm pixels, 20 mm tall) Shah et al. TNS 2004
The silicon photomultiplier (SiPM) Combine advantages of PMTs and APDs Still very expensive High gain (like PMTs) Insensitive to magnetic fields (e.g. for PET/MR) Excellent energy and timing resolution Temperature sensitive gain QuickTime and a decompressor are needed to see this picture. Simplified structure of a SiPM composed of G APD cells Roncali and Cherry, Ann Biomed Eng, 2011
PET/MR scanners
Clinical PET/MR scanner Siemens mmr first joint scanner (Philips and GE currently have 'tandem' systems) Uses APDs Expensive Attenuation correction for bone an open problem for all systems Clinical results from Drzezga et al, JNM June 2012 QuickTime and a decompressor are needed to see this picture. PET/CT PET/MR
CT dose reduction methods
Iterative CT image reconstruction Can be used in CT like it is in PET Computationally now tractable Several approaches under development for CT only scanners Gradually move to PET/CT scanners
AAPM 2012 Summer School on Medical Imaging using Ionizing Radiation RSD Phantom: 120 kvp 100 mas 25 mas 12 mas FBP air water water+ contrast MBIR
Cost effective PET/CT scanners
'Value based' PET/CT Refurbished PET/CT scanners Strong market New systems GE Optima 560 Philips Gemini LXL Siemens Excel 20 mct Seem to be based on reduced capabilities compared to full featured scanners