Performance Evaluation of Quantitative SPECT/CT: Applying NEMA NU2 PET Measurements to SPECT

SPECT and PET systems were tested using the methodology defined in NEMA NU 2-2012 Performance Measurements of Positron Emission Tomographs.$^{99}mTc$ and $^{177}Lu$were used to test on the SPECT (Symbia- Intevo, Siemens Healthcare) and $ 1S\Gamma $ was used for the PET (Biograph-mCT, Siemens Healthcare). The spatial resolution was measured in radial and tangential directions. Scatter fraction and count losses were measured with a line source inserted into a cylinder phantom. The sensitivity was measured using a uniform line source surrounded by aluminum sleeves ofvarying thickness. Five aluminum sleeves with different diameters were used to measure the attenuated count rate with accumulated wall thicknesses to extrapolate to “zero attenuation”The spatial resolution for radial/tangential directions at 1 cm were: 5.29/4.30 mm, 12.6/14.1 mm and $21.6~\mathrm {m}\mathrm {m}/23.4$ mm for $1S\Gamma, 99\mathrm {m}\mathrm {T}\mathrm {c}$ and $177\mathrm {L}\mathrm {u}$, respectively. The event rates of $^{99}mTc$ showed linear increase with activity. The sensitivities at $0/10\mathrm {c}\mathrm {m}$ off axis were: $9.63\times 10^{3}/9.59\times 10^{3}$ cps/MBq, 119.4/116.7 cps/MBq, and 47.6/47.5 cps/MBq for $1S\Gamma, 99\mathrm {m}\mathrm {T}\mathrm {c}$ and $177\mathrm {L}\mathrm {u}$, respectively. The scatter fractions of $1S\Gamma, 99\mathrm {m}\mathrm {T}\mathrm {c}$ and $^{177}Lu$were 0.32, 0.25 and 0.36. The background variability was 1.52%, 2.73% and 6.51% for $1S\Gamma, 99\mathrm {m}\mathrm {T}\mathrm {c}$ and $177\mathrm {L}\mathrm {u}$, respectively. The hot sphere contrast was 69.8%, 78.5% and 64.7% for $1S\Gamma, 99\mathrm {m}\mathrm {T}\mathrm {c}$ and $177\mathrm {L}\mathrm {u}$, respectively. True concentration ratio of $^{99}mTc$ and $^{177}Lu$on SPECT were 7.2:1 and 5.8:1, where $\mathrm {S}\mathrm {U}\mathrm {V}_{\max }$ in hot spheres and background SUVs were 6.9/0.98 and 5.5/10.4 for $^{99}mTc$ and $177\mathrm {L}\mathrm {u}$, respectively, on the quantitative SPECT images.This study underscores the transition of SPECT from a qualitative or semi-quantitative imaging modality to a fully quantitative clinical tool.