Comprehensive SPECT/CT system characterization and calibration for 177Lu quantitative SPECT (QSPECT) with dead-time correction

EJNMMI Physics

Table 3 Calibration factor and dead-time constant (± SE) derived from planar images

No. of acquisitions Activity range (MBq) Photopeak count rate range (cps) Wide-spectrum count rate range (cps)		Detector	Calibration factor (cps/MBq)			Dead-time constant (μs)
			Method A	Method B Photopeak	Method B Wide-spectrum	Method A Photopeak	Method B Photopeak	Method A Wide-spectrum	Method B Wide-spectrum
Low activity range	Full activity range		Method A	Method B Photopeak	Method B Wide-spectrum	Method A Photopeak	Method B Photopeak	Method A Wide-spectrum	Method B Wide-spectrum
7	30	1	9.42 ± 0.02	9.49 ± 0.01	9.44 ± 0.01	2.00 ± 0.01	2.06 ± 0.01	0.541 ± 0.001	0.547 ± 0.002
19–400	19–10,809	2	9.35 ± 0.03	9.32 ± 0.01	9.27 ± 0.02	2.13 ± 0.01	2.10 ± 0.01	0.573 ± 0.002	0.553 ± 0.004
208–4049	208–94,800	1 and 2	9.38 ± 0.03	9.40 ± 0.01	9.36 ± 0.01	2.07 ± 0.01	2.08 ± 0.01	0.557 ± 0.002	0.550 ± 0.003
850–14,400	850–355,034	1 and 2	9.38 ± 0.03	9.40 ± 0.01	9.36 ± 0.01	2.07 ± 0.01	2.08 ± 0.01	0.557 ± 0.002	0.550 ± 0.003

Method A refers to obtaining the calibration factor at low activity, i.e. a subset of the full activity range (Eq. 1), then obtaining the dead-time constant over the full activity range by fitting the paralysable model to the data (Eq. 3). Method B refers deriving both the calibration factor and the dead-time constant through a single curve fit with data from the full activity range (Eq. 3). The acquisition count rate from either the photopeak or the wide spectrum (6W, 18–680 keV, Table 2) was considered for dead-time constant determination