Performance Measurement of the microPET Focus 120 Scanner

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FIGURE 1.
Spatial resolution profile measured using a ²²Na point source. (A) Transaxial (radial and tangential). (B) Axial with or without oversampling. (C) Volume resolution with or without oversampling.
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FIGURE 2.
3D sensitivity profile over a FOV.
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FIGURE 3.
NECR vs. total radioactivity for mouse (A) and rat (B) phantoms.
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FIGURE 4.
Image of Micro Deluxe phantom with hot-rod inserts—reconstructed using the 3DRP algorithm.
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FIGURE 5.
Maximum-intensity projection (MIP) images of mouse bone ¹⁸F PET reconstructed using different algorithms: (A) FBP, (B) 3DRP, (C) EM, and (D) MAP.
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FIGURE 6.
Selected animal imaging studies. (A) Myocardial PET image of rat in end-diastolic phase. (B) Cat brain PET image acquired using ¹⁸F-FDG and reconstructed using the MAP algorithm.

TABLE 1

Specification Comparison of microPET Systems Related to Focus 120

Category	Specification	Focus 120	R4^*	Focus 220^†
Detector	Crystal material	LSO	LSO	LSO
	Crystal element size (mm³)	1.5 × 1.5 × 10	2.1 × 2.1 × 10	1.5 × 1.5 × 10
	Crystal pitch (mm)	1.59	2.45	1.59
	Crystal array	12 × 12	8 × 8	12 × 12
	Packing fraction (%)	92	80	92
System	Number of detector blocks	96	96	168
	Total number of crystal elements	13,824	6,144	24,192
	Number of rings	48	36	48
	Ring diameter (cm)	15	15	26
	Bore size (cm)	12	12	22
	Transaxial FOV (cm)	10	10	19
	Axial FOV (cm)	7.6	7.8	7.6
	Solid angle/4π	0.45	0.46	0.28

TABLE 3

Scatter Fraction and Counting Rate Performance

Phantom	Energy window (keV)	Coincidence window (ns)	Scatter fraction (%)	Peak true (kcps at kBq/mL)	Peak NECR (kcps at kBq/mL)
Mouse	250∼750	6	15.9	1,296 at 3,242	869 at 3,242
		10	15.0	1,218 at 2,136	793 at 2,136
	350∼650	6	11.6	1,088 at 3,684	741 at 2,989
		10	11.0	1,092 at 3,108	689 at 2,781
Rat	250∼750	6	35.0	582 at 448	228 at 290
		10	34.9	585 at 358	199 at 262
	350∼650	6	22.9	449 at 506	201 at 289
		10	23.1	466 at 498	175 at 260

TABLE 4

Comparison of Performance Characteristics in microPET Scanners

Performance characteristic		Focus 120 (this study)	Focus 120 (Laforest et al.)^*	R4^†	Focus 220^‡
Energy resolution (%)		18.3	N/A	23	18.5
Volumetric resolution (μL)^§	Center	1.92	2.87	5.1	2.5^¶
	1-cm radial offset	6.41	N/A	15.6	N/A
	2-cm radial offset	8.14	8.23	∼19^‖	6.3^¶
Absolute sensitivity for point source at center (%)	250∼750 keV, 10 ns	7.0	7.1	N/A	3.4
	250∼750 keV, 6 ns	6.7	6.7^**	4.37	3.0
	350∼650 keV, 10 ns	4.0	4.7^**	N/A	N/A
	350∼650 keV, 6 ns	3.8	4.4^**	2.45	2.1
Scatter fraction (%)^††	Mouse phantom	15.9	12.3	32.0	19.0
		(3-cm Ø, 7-cm L)	(2.5-cm Ø, 7-cm L)	(4.3-cm Ø, 7.6-cm L)	(3-cm Ø, 7-cm L)
	Rat phantom	35.0	26.3	38.0	36.4
		(6-cm Ø, 15-cm L)	(5-cm Ø, 15-cm L)	(6-cm Ø, 9.6-cm L)	(6-cm Ø, 15-cm L)
Peak NECR (kcps)^††	Mouse phantom	869 at 160.58 MBq	809 at 88.8 MBq	174 at 76.96 MBq	645 at 146.52 MBq
		(4.34 mCi)	(2.4 mCi)	(2.08 mCi)	(3.96 mCi)
		(3-cm Ø, 7-cm L)	(2.5-cm Ø, 7-cm L)	(4.3-cm Ø, 7.6-cm L)	(3-cm Ø, 7-cm L)
	Rat phantom	228 at 122.84 MBq	300 at 149.85 MBq	94 at 59.94 MBq	177 at 143.19 MBq
		(3.32 mCi)	(4.05 mCi)	(1.62 mCi)	(3.87 mCi)
		(6-cm Ø, 15-cm L)	(5-cm Ø, 15-cm L)	(6-cm Ø, 9.6-cm L)	(6-cm Ø, 15-cm L)

↵* Data published by Laforest et al. (13).
↵† Data published by Knoess et al. (19).
↵‡ Data published by Tai et al. (12).
↵§ Data were not corrected for source dimension, positron range, or acolinearity of positron annihilation and were estimated from nonoversampled axial profiles except for Focus 220.
↵¶ Axial resolution was estimated from oversampled axial profiles (Tai et al.) (12).
↵‖ Estimated from Figure 5 in Knoess et al. (19).
↵** Estimated from Figure 1 in Laforest et al. (13).
↵†† Data were measured using same energy window (250–750 keV) and coincidence window (6 ns) but the phantom sizes (Ø, diameter; L, length) were not identical.
N/A = not available.