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

EJNMMI Physics

Table 4 Calibration factor and dead-time constant (± SE) derived from SPECT data

Phantom	Low activity	Full activity range	Calibration factor (cps/MBq)			Dead-time constant (μs)
Phantom	No. of acquisitions Activity range (MBq) Photopeak count rate range (cps) Wide-spectrum count rate range (cps)		Method A	Method B Photopeak	Method B Wide-spectrum	Method A Photopeak	Method B Photopeak	Method A Wide-spectrum	Method B Wide-spectrum
Air-3D	7 32-330 327-3154 1342-11,975	27 32-10,704 327-88,762 1342-347,060	9.62 ± 0.04	9.70 ± 0.03	9.67 ± 0.03	2.07 ± 0.01	2.15 ± 0.03	0.531 ± 0.003	0.544 ± 0.008
CTDI-10	4 126-510 800-3423 5229-20,267	19 13-9646 93-60,750 665-354,256	9.91 ± 0.06	9.72 ± 0.03	9.70 ± 0.03	3.18 ± 0.02	2.93 ± 0.04	0.546 ± 0.005	0.499 ± 0.008
CTDI-16	5 157-634 693-3302 5523-22,333	16 16-80,94 83-41,651 694-264,231	9.98 ± 0.09	9.84 ± 0.05	9.85 ± 0.06	3.77 ± 0.06	3.28 ± 0.12	0.603 ± 0.010	0.528 ± 0.024
CTDI-32	4 293-1404 522-2364 5226-23,734	20 21-13,708 50-53,746 513-339,364	10.66 ± 0.09	10.19 ± 0.05	10.23 ± 0.04	4.47 ± 0.08	3.71 ± 0.07	0.705 ± 0.011	0.594 ± 0.012
Jaszczak	5 120-526 624-2335 4972-17,052	26 44-12,480 307-49,376 2650-348,334	9.50 ± 0.05	9.40 ± 0.05	9.46 ± 0.04	4.07 ± 0.04	4.04 ± 0.09	0.572 ± 0.005	0.565 ± 0.010

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 data to the paralysable model (Eq. 3). Method B refers deriving both the calibration factor and the dead-time constant through a single curve fit using 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