rb 82 cardiac pet scanning protocols and dosimetry · rb‐82 cardiac pet scanning protocols and...

Rb‐82 Cardiac PETScanning Protocols and Dosimetry

Deborah ToutNuclear Medicine Department

Central Manchester University Hospitals

Overview

• Rb‐82 myocardial perfusion imaging protocols– Acquisition

– Reconstruction

• Optimisation of protocols

• Patient dosimetry

• Staff dose

Rubidium‐82

Advantages

• Available at sites without a cyclotron

• Short T1/2 (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

Rubidium‐82

Disadvantages

• Relatively long positron range

– Reduction in spatial resolution

• Short T1/2 (75 sec)

– Poor count statistics

• Pharmacological stress only

[1] Beller et al JNC 2004; 11:71‐86

Most widely used radiotracer for clinical PET MPI1

Equipment

CardioGen‐82 generator, manufactured by Bracco, supplied in the UK by Imaging Equipment Ltd (IEL)

Siemens Biograph mCT PET CT

Acquisition Protocol

topogram22cm

CTAC Rest

Adenosine infusion (4.5mins)

PET Stress(7min scan)

82Rb infusion 1110 MBq(2.0‐2.5 mins after adenosine)

(∼10‐20 sec)

[CTAC Stress]

PET Rest(7min scan)

82Rb infusion 1110MBq(∼10‐20 sec)


• Use PET monitor to see when to start acquisition


• Check PET‐CT registration prior to end of PET acquisition

• Translation allowed, rotation not allowed

• Determine if stress CTAC is required

Image Reconstruction

list mode data acquisition (7 mins)

0 1 2 3 4 5 6 7

Rb‐82 infusion static & ECG‐gated perfusion

image reconstruction 2.5 – 7.0 min

• Static and gated image reconstruction– 3D OSEM (2it, 21ss) with Siemens UltraHD∙PET

– 128 × 128 matrix & 2× zoom (voxel dimensions 3.18 × 3.18 × 2.03 mm)

– 6.5mm Gaussian post filter ‐ significant smoothing to suppress noise

– Attenuation & scatter correction (including prompt gamma correction)

– 8 bins for gating

Image Reconstruction

list mode data acquisition (7 mins)

0 1 2 3 4 5 6 7

Rb‐82 infusion

Dynamic Reconstruction (18 frames)1 × 10 secs8 × 5 secs3 × 10 secs2 × 20 secs4 × 60 secs

Protocol Optimisation

• Administered activity

• Reconstruction parameters

• Image reconstruction delay time

• Dynamic first pass imaging reconstruction and framing strategy

Protocol Optimisation: Administered Activity

Good Quality Perfusion Data3D acquisition

High administered activities

Recommended 40‐60 mCi (1480 – 2220 MBq)

MBF Quantification in Same Protocol?First pass dynamic imaging

Extremely high count rates

Potential for detector saturation

Detrimental to accurate MBF quantification

• Rb‐82 perfusion and MBF in a single protocol


• Detector saturation in 15% (33/217) of studies with 40 mCi Rb‐822

• Independent of patient gender, BMI or age of generator

• Transit of Rb‐82 through the axillary vessels in early frames

left arm

right arm

[2] Tout et al NMC 2012; 33(11):1202‐1211

Frame 3

Frame 4

Frame 5

Frame 6

Frame 7

Frame 1

Frame 2


• Reduced activity from 40 mCi (1480 MBq) to 30 mCi (1110 MBq)2

• Mild saturation observed in only 1% (2/159) of studies

[2] Tout et al NMC 2012; 33(11):1202‐1211

• No reduction in perfusion image quality

• Reduction in patient radiation dose of 25%

0%

20%

40%

60%

80%

0 1 2 3 4Image Quality Score

0 (unacceptable) to 4 (excellent)

30mCi Obs 1

30mCi Obs 2

40mCi Obs 1

40mCi Obs 2

Scoring of perfusion images by 2 blinded

experienced observers

No difference in image quality

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 MPI3

– Improves image contrast, defect definition and CNR in phantom and patient studies

• Benefits of TOF information4

– More signal, less noise & greater benefit for larger patients

– Benefit in Rb‐82 MPI?

[3] Le Meunier et al JNC 2010; 17:414‐426 [4] Karp et al JNM 2008; 49(3):462‐470

Protocol Optimisation: Reconstruction Algorithm

• Investigate addition of TOF information in static perfusion images5

• 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

[5] Armstrong et al. Abstract submitted for presentation at ICNC11, Berlin, May 2013.

Reduction in noise (COV) when TOF information

Greatest reduction in COV at highest weights

Patient size is less influential on image noisewhen TOF information is included

COV = SDmean

Example: 114 kg MaleOSEM

OSEM+PSF+TOF

is included

Protocol Optimisation: Reconstruction Delay

• Reconstruction delay of perfusion images

Longer delayBetter 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

Protocol Optimisation: Reconstruction Delay

No difference in noise (COV) in bullseye plot

Reduction in M:LV contrast

0%

10%

20%

30%

40%

50%

60%

70%

80%

1 2 3 4 5

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)

Scoring of perfusion images by blinded experienced observer

No significant difference in image quality or M:LV contrast

• Reduced static scan delay from 2.5 mins to 2.0 mins

GOOD M:LV

CONTRAST

POORM:LV

CONTRAST

Protocol Optimisation

• Administered activity

• Reconstruction parameters

• Image reconstruction delay time

Reduced from 40 mCi (1480 MBq) to 30 mCi (1110 MBq)

Using “advanced” OSEM reconstruction (Siemens UltraHD∙PET) with PSF and TOF information

2.5 min scan delay provides optimum trade off between count statistics and M:LV contrast

Patient Dosimetry: CT

• 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

• Attenuation Correction– Quality ref. eff. mAs 7; 120kV; 0.5s; pitch

1.5, 16x1.2mm collimation– Effective dose 0.3mSv

∼70kg ∼ 110kgSiemens Biograph mCT (Definition AS 64 slice)

Patient Dosimetry: Radiopharmaceutical

RadiopharmaceuticalARSAC DRL

(MBq)ED

(mSv)Typical Dose

(MBq)ED

(mSv)

Tc‐99m sestamibi6 1600 16 800 8

Tc‐99m tetrofosmin6 1600 12 800 6

Tl‐2016 120 21 80 16

Rb‐827 ‐ ‐ 2220 2.8

• For combined stress & rest myocardial perfusion imaging:

[6] ARSAC Notes for Guidance [7] Senthamizhchelvan et al JNM 2010; 51:1592‐1599

Patient Dosimetry

• Typical effective dose to patient– 2×1110 MBq Rb‐82 2.8 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

– 2×1110 MBq Rb‐82 2.8 mSv

– 2×CTAC (Q. ref. eff. mAs 7) 0.6 mSv– Total 5.2 mSv

• 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

• Reduction in staff dose is a consequence of remote administration

Staff Dose

Staff SPECT (µSv) PET (µSv)

Stressor 0.4 0.3

Technician 2.7 0.3

TOTAL 3.1 0.6

[8] Davidson et al. EJNM 2011; 38(Suppl 2):93‐228

Staff Dose

PositionMean (±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)

PET CT gantry

scan bed

82Rb cart

AB

C • Clinical need to be in scan room

• Measured dose rate at various locations

• A, B, C, C + lead WB shield

Time in Close Contact (min)

Mean Cumulative Dose (μSv)

7 3.2

15 6.8

30 13.4

60 26.0

Close Contact with Rb‐82 Patient Close Contact with Tc‐99m Patient

Scanning Protocols & Dosimetry

Thank [email protected]

rb 82 cardiac pet scanning protocols and dosimetry · rb‐82 cardiac pet scanning protocols and...

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