Rb 82 Cardiac PET Scanning Protocols and Dosimetry. Deborah Tout Nuclear Medicine Department Central Manchester University Hospitals

Transcription

1 Rb 82 Cardiac PET Scanning Protocols and Dosimetry Deborah Tout Nuclear Medicine Department Central Manchester University Hospitals

2 Overview Rb 82 myocardial perfusion imaging protocols Acquisition Reconstruction Optimisation of protocols Patient dosimetry Staff dose

3 Rubidium 82 Advantages Available at sites without a cyclotron Short T 1/2 (75 sec) Fast serial rest/stress imaging Single patient visit Lower radiation exposure to patient Peak stress images Extraction fraction similar to Tc 99m agents

4 Rubidium 82 Disadvantages Relatively long positron range Reduction in spatial resolution Short T 1/2 (75 sec) Poor count statistics Pharmacological stress only Most widely used radiotracer for clinical PET MPI 1 [1] Beller et al JNC 2004; 11:71 86

5 Equipment CardioGen 82 generator, manufactured by Bracco, supplied in the UK by Imaging Equipment Ltd (IEL) Siemens Biograph mct PET CT

6 Acquisition Protocol topogram 22cm 82 Rb infusion 1110MBq ( sec) CTAC Rest PET Rest (7min scan) Adenosine infusion (4.5mins) 82 Rb infusion 1110 MBq ( mins after adenosine) ( sec) PET Stress (7min scan) [CTAC Stress]

7 Acquisition Protocol Use PET monitor to see when to start acquisition

8 Acquisition Protocol Check PET CT registration prior to end of PET acquisition Translation allowed, rotation not allowed Determine if stress CTAC is required

9 Acquisition Protocol

10 Image Reconstruction Rb 82 infusion static & ECG gated perfusion image reconstruction min list mode data acquisition (7 mins) Static and gated image reconstruction 3D OSEM (2it, 21ss) with Siemens UltraHD PET matrix & 2 zoom (voxel dimensions mm) 6.5mm Gaussian post filter significant smoothing to suppress noise Attenuation & scatter correction (including prompt gamma correction) 8 bins for gating

11 Image Reconstruction Rb 82 infusion list mode data acquisition (7 mins) Dynamic Reconstruction (18 frames) 1 10 secs 8 5 secs 3 10 secs 2 20 secs 4 60 secs

12 Protocol Optimisation Administered activity Reconstruction parameters Image reconstruction delay time Dynamic first pass imaging reconstruction and framing strategy

13 Protocol Optimisation: Administered Activity Rb 82 perfusion and MBF in a single protocol Good Quality Perfusion Data 3D acquisition High administered activities Recommended mci ( MBq) MBF Quantification in Same Protocol? First pass dynamic imaging Extremely high count rates Potential for detector saturation Detrimental to accurate MBF quantification

14 Protocol Optimisation: Administered Activity Detector saturation in 15% (33/217) of studies with 40 mci Rb 82 2 Independent of patient gender, BMI or age of generator Transit of Rb 82 through the axillary vessels in early frames left arm Frame 1 Frame 2 Frame 3 right arm Frame 4 Frame 5 Frame 6 Frame 7 [2] Tout et al NMC 2012; 33(11):

15 Protocol Optimisation: Administered Activity Reduced activity from 40 mci (1480 MBq) to 30 mci (1110 MBq) 2 Mild saturation observed in only 1% (2/159) of studies Scoring of perfusion images by 2 blinded experienced observers No difference in image quality 80% 60% 40% 20% 0% Image Quality Score 0 (unacceptable) to 4 (excellent) 30mCi Obs 1 30mCi Obs 2 40mCi Obs 1 40mCi Obs 2 No reduction in perfusion image quality Reduction in patient radiation dose of 25% [2] Tout et al NMC 2012; 33(11):

16 Protocol Optimisation: Reconstruction Algorithm Available reconstruction algorithms Standard 3D iterative reconstruction (OSEM) Advanced OSEM with point spread function (PSF) modelling (resolution recovery) and time of flight (TOF) information Benefits of including PSF information for Rb 82 MPI 3 Improves image contrast, defect definition and CNR in phantom and patient studies Benefits of TOF information 4 More signal, less noise & greater benefit for larger patients Benefit in Rb 82 MPI? [3] Le Meunier et al JNC 2010; 17: [4] Karp et al JNM 2008; 49(3):

17 Protocol Optimisation: Reconstruction Algorithm Investigate addition of TOF information in static perfusion images 5 74 patients with BMI from 20.8 kgm 2 to 55.8 kgm 2 Coefficient of variation (COV) of pixel values in bullseye plot as a measure of image noise COV = SD mean Example: 114 kg Male OSEM OSEM+PSF+TOF Reduction in noise (COV) when TOF information is included Greatest reduction in COV at highest weights Patient size is less influential on image noise when TOF information is included [5] Armstrong et al. Abstract submitted for presentation at ICNC11, Berlin, May 2013.

18 Protocol Optimisation: Reconstruction Delay Reconstruction delay of perfusion images Longer delay Better myocardium to LV cavity (M:LV) contrast Shorter delay Better count statistics Initial protocol 2.5 min delay Other centres use 2.0 min or 1.5 min delay

19 Protocol Optimisation: Reconstruction Delay Reduced static scan delay from 2.5 mins to 2.0 mins Scoring of perfusion images by blinded experienced observer No significant difference in image quality or M:LV contrast 80% 70% 60% 50% 40% 30% 20% 10% 0% 2.0 min Image Quality 2.5 min Image Quality 2.0 min M:LV Contrast 2.5 min M:LV Contrast Image Quality Score 0 (unacceptable) to 4 (excellent) GOOD M:LV CONTRAST POOR M:LV CONTRAST No difference in noise (COV) in bullseye plot Reduction in M:LV contrast

20 Protocol Optimisation Administered activity Reduced from 40 mci (1480 MBq) to 30 mci (1110 MBq) Reconstruction parameters Using advanced OSEM reconstruction (Siemens UltraHD PET) with PSF and TOF information Image reconstruction delay time 2.5 min scan delay provides optimum trade off between count statistics and M:LV contrast

21 Patient Dosimetry: CT Siemens Biograph mct (Definition AS 64 slice) Attenuation Correction Quality ref. eff. mas 11; 120kV; 0.5s; pitch 1.5, 16x1.2mm collimation Effective dose 0.4mSv Calcium Scoring Quality ref. eff. mas 60; 120kV, 0.238s, axial, 18mm collimation Effective dose 1.8mSv 70kg 110kg Attenuation Correction Quality ref. eff. mas 7; 120kV; 0.5s; pitch 1.5, 16x1.2mm collimation Effective dose 0.3mSv

22 Patient Dosimetry: Radiopharmaceutical For combined stress & rest myocardial perfusion imaging: Radiopharmaceutical ARSAC DRL (MBq) ED (msv) Typical Dose (MBq) ED (msv) Tc 99m sestamibi Tc 99m tetrofosmin Tl Rb [6] ARSAC Notes for Guidance [7] Senthamizhchelvan et al JNM 2010; 51:

23 Patient Dosimetry Typical effective dose to patient MBq Rb msv 1 CTAC (Q. ref. eff. mas 11) 0.4 msv Total 3.2 msv Maximum effective dose to patient 1 CaScCT (Q. ref. eff. mas 60) 1.8 msv MBq Rb msv 2 CTAC (Q. ref. eff. mas 7) 0.6 msv Total 5.2 msv

24 Staff Dose Use EPD to measure dose to stressor (stress injection) and technician (stress assistance, rest injection, stress/rest imaging) Table shows total dose to staff per patient (stress & rest) 8 Staff SPECT (µsv) PET (µsv) Stressor Technician TOTAL Reduction in staff dose is a consequence of remote administration [8] Davidson et al. EJNM 2011; 38(Suppl 2):93 228

25 Staff Dose C Clinical need to be in scan room A 82 Rb cart PET CT gantry B scan bed Measured dose rate at various locations A, B, C, C + lead WB shield Close Contact with Rb 82 Patient Position Mean (±SD) Cumulative Dose over 7 min (μsv) A 59.2 (±6.1) B 3.1 (±0.5) C 9.5 (±1.7) C + Shield 2.7 (±0.5) Close Contact with Tc 99m Patient Time in Close Contact (min) Mean Cumulative Dose (μsv)

26 Scanning Protocols & Dosimetry Thank You!