Absolute quantification of bone scintigraphy provided by a whole-body 360 degrees CZT SPECT/CT camera in patients with vertebral fractures

1134 Introduction: Bone scintigraphy (BS) is routinely performed for assessing vertebral fractures (VF), although this investigation is mainly based on subjective visual analysis. Nowadays, absolute quantification using SUV values may be obtained on bone SPECT recordings provided by new SPECT/CT systems. This study aimed to determine whether the absolute quantification of bone scintigraphy provided by the Veriton® CZT-SPECT/CT system (Spectrum Dynamics Medical) is accurate, as assessed through phantom experiments, and whether it provides consistent results for monitoring VF healing.\n Methods: SPECT/CT images were recorded on the Veriton® system and reconstructed with corrections for attenuation and scatter, resolution recovery and partial volume correction. In a first step, absolute quantification was assessed on three vials with known volumes (0.5 L) filled-in with a 99mTc-solution and different iodine concentrations replicating the densities and Hounsfield Units (UH) corresponding to the range of those from soft tissues (3.6 HU), and from spongy (203.5 HU) and cortical (704.2 HU) bone. In a second step, this quantification was applied to paired 99mTc hydroxymethylene diphosphonate-scintigraphy obtained in 25 patients (age: 74±12 years, 56% male) who had undergone imaging at baseline, 1.3±1.1 months after an acute VF; and follow-up at 5.2±2.3 months.\n Results: On phantoms (ie. vials), the % errors for SPECT determination of activity concentrations were 2.0, 1.0 and 0.1% for densities corresponding respectively to, soft tissue, spongy and cortical bone materials. In patients, SUVmax values from reference non-fractured T1 vertebrae were rather low and not significantly different between baseline and 5-month follow-up imaging (5.7±1.1 vs. 5.8±1.1, p=0.76). The VF SUVmax values were on average 3-fold higher than the corresponding T1 values at baseline (21.0±8.5, p\u003c0.001 in comparison to T1 SUVmax). These VF SUVmax values were markedly decreased at the 5-month follow-up (11.2±4.2, p\u003c0.001 vs. baseline), but still remained significantly higher than the corresponding T1 values (p\u003c0.001 in comparison to T1 SUVmax at 5-months follow-up) even though the fractured sites were difficult to detect by conventional visual analysis at that time.\n Conclusions: The whole-body Veriton® CZT-SPECT/CT system provides 1) accurate absolute quantification of 99mTc-activity, as evidenced by phantom experiments, and 2) consistent results for the SUV-based assessment of bone scintigraphy, with the notable observation of a reduction in SUV over time for vertebrae affected by fractures.