Abstract
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Objectives: Bone scintigraphy with 99mTc-labeled bone scintigraphic agents such as methylene diphosphonate (MDP) and hydroxymethylene diphosphonate (HMDP) have been widely used for the assessment of bone diseases. On bone scintigram, however, quantitative assessment has not been usually performed because of the lack of appropriate methods. Recently, a scanner combining SPECT and CT has gained widespread acceptance. The SPECT/CT scanners can provide attenuation correction maps that are necessary for quantitative analyses using standardized uptake ratio (SUV). The purpose of this study was to determine SUV in normal bone using a quantitative SPECT/CT protocol.
Methods: Total 128 consecutive patients (M/F=94/34; mean age, 68±13) who underwent bone SPECT/CT with 99mTc-MDP (n=65) or 99mTc-HMDP (n=63) for screening bone metastasis were studied. All data were acquired with a combined SPECT/CT scanner (Discovery NM/CT 670, GE). SPECT data acquisition (60 steps of 8 s/step, 360 degree, 128x128 matrix) covering from the cervical region to the proximal femora was performed 2 hours after the radiotracer injection with a low-energy high-resolution collimator. SPECT images were reconstructed with attenuation correction and scatter correction using ordered-subset expectation maximization algorithm (2 iterations, 10 subsets). Non-contrast CT images were used for the attenuation correction. In order to determine normal bone SUVmax, cube-shaped volume of interest (VOI) with 20mm edge was placed over the sites of normal bone. Using a calibration factor and a dedicated software (Q.Metrix, GE), the SPECT count within the VOI was converted to SUV. The bone sites analyzed were C4, Th6, and L3 vertebral body, mid sacrum, mid sternum, right anterior and posterior iliac bone, and intertrochanteric right femur. Normal bone was defined as a region of skeleton exhibiting mild diffuse uptake, without any focal uptake and without anatomic abnormalities on CT.
Results: The mean normal SUVmax for 99mTc-MDP and 99mTc-HMDP were: cervical vertebrae 4.32±1.22 and 4.68±1.33, thoracic vertebrae 5.11±1.32 and 5.63±1.60, lumbar vertebrae 5.07±1.33 and 5.86±1.66, mid sacrum 3.77±1.12 and 4.62±1.44, mid sternum 2.85±0.79 and 3.04±1.12, anterior iliac bone 4.19±1.39 and 5.05±1.60, posterior iliac bone 4.63±1.38 and 5.74±2.07, and femur 2.73±0.84 and 2.99±1.43, respectively. Figure 1 shows the distribution of SUVmax in a boxplot. Mild inverse correlation was found between the 99mTc-HMDP SUVmax of vertebral bodies and iliac bones and the patient’s age (e.g. lumbar vertebrae, r=-0.37, p=0.0035; anterior iliac bone, r=-0.45, p=0.0002). There was no relationship between the SUVmax measurements of all bone sites and the gender.
Conclusion: SUV can be used to quantify both 99mTc-MDP and 99mTc-HMDP bone SPECT/CT studies. If the SUV of the normal skeleton are known, they can be used in the characterization of bone lesions and in the assessment of treatment response to bone diseases. Research Support: None