A retrospective study of SPECT/CT scans using SUV measurement of the normal lumbar vertebrae with Tc-99m methylene diphosphonate

Objective: The aim of this study was to acquire the SUVs for each segment of the vertebral body to explore the rationale for the large variability of the SUVs in normal vertebrae. Methods: This retrospective study was performed using the images and data from 39 cancer patients who underwent bone SPECT/CT scans with Tc-99m MDP. The SUVmax and SUVmean of the anterior, middle, posterior; left, middle, right; top, middle, and lower of the lumbar vertebrae 1~5, were calculated. The continuous variables were represented by the median values (Q1,Q3), and the differences among various segments were analyzed by Friedman’s nonparametric test. The pairwise comparison between groups was corrected by the Bonferroni method. The P<0.05 was considered statistically signifi cant. Results: In this study, 39 patients (31 women and 8 men; mean age, 54.79±9.12 years; age range, 39–71 years) were elucidated. The SUVmax of the L1 and L3 vertebral bodies’ parts were signifi cantly different from those of the other portions of the same lumbar vertebra. The SUVmax of the lower posterior portion of the L1 vertebral body was signifi cantly different from that of the upper posterior portion. There were signifi cant differences in the SUVmax between the upper and lower portions, middle and lower portions in the middle of the L3 vertebral body. The SUVmean of the lower posterior portion of L1 and L2 vertebral were signifi cantly different from those of the upper posterior portion. There were signifi cant differences in the SUVmean between the upper and lower portions of the middle of the L3 vertebral body. There were signifi cant differences among the SUVmax and SUVmean of the right, and middle of the vertebral body except for the L2 vertebral body. There were signifi cant differences among the SUVmax and SUVmean of the anterior, middle segments of the lumbar vertebrae body, and the SUVmax of the anterior and posterior parts of the L2 vertebral body, and the SUVmean of the middle and posterior parts of the L1 vertebra. The SUVmax of the middle and posterior portions of the L3~L5 vertebral body, and the SUVmean of the L1 ~L3, and L5 lumbar vertebrae had signifi cant differences. Conclusion: The difference in the bone metabolism of the lumbar vertebral body is caused by the variation in the horizontal direction of the vertebral body. The bone metabolism in the vertical direction of the lumbar vertebrae has more uniformity. As a quantitative imaging measure, the SUVs might require standardization with adequate reference data to minimize the variability in the participants. Research Article A retrospective study of SPECT/ CT scans using SUV measurement of the normal lumbar vertebrae with Tc-99m methylene diphosphonate Ruifeng Wang1, Cong Shen2, Dong Han1, Zhaoguo Zhang1, Yuhong Zeng3, Hulin Wu1, Xiaotong Xu1, Tao Qin1, Nan Yu1, Yongjun Jia1, Pengtian Zhang1, Taiping He1, Guo youmin2 and Yan Feng3* 1Department of Medical Image, the Affi liated Hospital of Shanxi University of Chinese Medicine, Shananxi, China 2Department of Medical Image, the First Affi liated Hospital of Xi’an Jiaotong University, Xi’an, China 3Department of Osteoporosis, Honghui Hospital, Xi’an Jiaotong University, Xi’an, China Received: 08 March, 2021 Accepted: 05 April, 2021 Published: 07 April, 2021 *Corresponding author: Yan Feng, Department of osteoporosis, Honghui Hospital, Xi’an Jiaotong University, No. 555 East Youyi Road, Xi’an City, Shaanxi, 710054, China, Tel: +86 29 62818587; E-mail:


Introduction
The skeleton is the most frequent site for tumor metastasis.
The extent of metastasis is the prognostic indicator in cancer patients following treatment [1,2]. Various types of tumors cause the different relative incidence of bone metastasis and the median-survival time in cancer patients [3]. The spine and pelvis are the most common sites for secondary bone metastases for different primary cancers [2,4].
The Technetium-99m labeled bone scintigraphic agent Methylene Diphosphonate (MDP) which binds to the mineral phase of bone hydroxyapatite and the calcium-rich tissue has been widely used in bone scintigraphy in metastatic bone diseases in the past [5,6]. Planar imaging has been mainly performed in bone scintigraphy, and Single-Photon Emission Computed Tomography (SPECT) has also been performed in body parts with a limited range of clinical diagnosis value.
The Single-Photon Emission Tomography (SPECT)/Computed Tomography (CT) scanner combining SPECT and Computed Tomography (CT) has gained widespread acceptance. The SPECT/CT scanner provides fusion images of CT and SPECT and produces attenuation correction maps necessary for quantitative analysis using the Standardized Uptake Value (SUV) [2,5,7,8]. The SUV integrates the concept of biomarker and the notion of quantitative imaging. A Quantitative Imaging Biomarker (QIB) uses objectively measured characteristics derived from an in vivo image and serves as an indicator of normal biological processes, pathological processes, or response to a therapeutic intervention [8]. The Quantitative measurements which have been defi ned as the extraction of quantifi able features from the medical images to determine the normality or the degree of alteration, or the status of a disease, injury, or chronic condition relative to the normal have been vastly used with the advances in molecular imaging [8,9].
The bone scans of vertebrae were quantitatively analyzed using the SUV as QIB of SPECT/CT scans with Tc-99m-MDP [5,8,10,11]. Jun Zhao's study evaluated SUVmax and SUVmean of benign bone lesion and malignant bone metastasis foci of normal vertebrae, which provide a quantitative reference for clinical diagnosis and the evaluation of therapeutic response in vertebral lesions [12]. The bone tissue blood fl ow and osteoblastic activity is proportional to bone tissue uptake of 99mTc-MDP [13,14]. bones at different sites can have different normal SUVs [5,8]. SUVmax and SUVmean were proved to be signifi cantly different between male and female patients in most vertebrae [12]. Hence, as a quantitative imaging biomarker, SUVs of normal vertebrae showed relatively large variabilities [5,14]. The SUVs for each vertebral level are different with signifi cant variabilities [2]. Thus, it is critical to elucidate how to reduce the large variability of the SUV of normal vertebrae. The huge variability of SUVs in a lumbar vertebra may have resulted from the uneven metabolism in the vertebral body. Therefore, the primary aim of this study was to elucidate the SUVs for each segment of the vertebral body to explore the rationale behind the large variability of SUVs in normal vertebrae.

Patients
In this study, we retrospectively analyzed the imaging data of patients who underwent bone scans to explore the metastasis from various cancers such as prostate cancer,  of the spine was also characterized by correlating the tracer uptake with its CT morphological image, which encompassed osteophytes, end plates, facet joints, and the area around the joints.

SPECT/CT image analysis
The Whole-Body Scan (WBS) and SPECT/CT images were independently interpreted by two experienced nuclear medicine professors and a diagnostic radiologic professor. In cases of discrepancies, the consensus was obtained by a joint reading.
The SUVs of 39 lumbar vertebrae were included for the analyses based on the previously defi ned criteria [5]. The patients were included based on the following criteria: (1) access to data on measured injection activity, time of measurement, and time of injection; (2) access to patient's weight and height information; The SUV was calculated as follows:   Non-neoplastic patient 1 Figure 1: Transaxial, sagittal, and coronal images of a patient's SPECT/CT combined data of a lumbar vertebra. The VOIs of the lumbar vertebra were plotted by manually adjusting the boundary of the SPECT and that of the spongy bone of the lumbar vertebra on CT images. R represents right group; M represents middle group, L represents the left group, A represents anterior parts of lumbar vertebrae, MM represents middle parts of lumbar vertebrae, and P represents posterior parts of lumbar vertebrae.    (Tables 6,7).

Discussion
The SUV might be useful as an appropriate quantitative measure in skeletal SPECT/CT imaging and has been frequently used in evaluating the activities of bone lesions     Note: Continuous variables were expressed as median (Q1, Q3), and the pair comparison was corrected by Bonferroni method. * represents a statistical difference compared with the R group, # represents a statistical difference compared between the M group and L group    and the response to therapy [7,15,16]. Since the SUV refl ects the osteoblastic activity, and the concentration of the boneseeking agents would be directly correlated to the SUV [13,17].
However, It is diffi cult to determine a standard value for a normal bone since the measure was based on the body weight of the normal vertebrae with wide variability [5,18]. In this study, the SUVmax and SUVmean that were based on the body weight of various parts of the vertebral body such as anterior, middle, and posterior parts, and left, middle, and right segments of lumbar vertebra were calculated.
In this current study, there were no statistical differences in most SUVs of the upper, middle, and lower parts of the lumbar vertebral body. In the human vertebrae, the trabeculae's thickness and length of a normal cancellous bone designate the physiologic compressive and tension stresses of the bone.
The trabeculae of a cancellous bone can remodel in orientation, number, and structure to accommodate and distribute the stresses to which the bone is exposed [19]. Therefore, the Banse, et al. [16] demonstrated that the vertical inhomogeneity was clearly pronounced in the images because the lower half of the vertebral body had a lower density than the upper half of the vertebral body. The differences ranged from 15% to 25% in their study. In the thoracolumbar and lumbar vertebrae, the numbers of nodes or node-to-node struts were two-fold higher in the inferior half than in the superior half of the vertebral body. The trabecular thickness and number of freeends manifested a center or a close-to-endplate structural pattern, with the central trabeculae being 15% thicker than the close-to-endplate. Further, the central trabeculae had 30% fewer free-ends than the close-to-end plate in the same study [21]. These inferences might be the rationale for the This current research showed that Signifi cant differences were widely observed among SUVmax and SUVmean measures in the right, middle and left parts of the lumbar vertebrae ( Table   4). The lumbar vertebral bodies have two ossifi cation centers, which merge and form single ossifi cation centers on each side of the vertebral arch [25]. The Tc-99m-DPD bone uptake depended on the bone osteoblastic activity, vascularization, and environmental factors [14]. In the present study, when the left,  (Table 5). Banse et al. found that the structural differences between anterior, posterior, and external areas were inapparent and followed the density patterns. The cancellous bone density was 20% higher in the posterior cores than the anterior and external cores [21]. The regional morphometry and subregional density of the cancellous bones had signifi cant differences with age and sex [26][27][28]. In the human vertebrae, the lumbar vertebrae play roles in both weight-bearing and load-transfer. The vertical bone trabeculae follow the lines of compressive stresses and are the primary load-bearing structure of the cancellous bone in the vertebrae, whereas the horizontal bone trabeculae are the main structure to distribute the stress and absorb the energy [19]. During aging, there is a non-uniform loss of bone within the vertebral body, resulting in non-homogeneous density throughout the centrum of the trabecular bone [19,29,30]. These sequels may have resulted from the regional compressive load-bearing and strong energy absorption capacity of the osteoporotic population.
The main limitation of the study subjects was tumor patients without bone metastasis, which might have an inapparent selective deviation from a typically normal bone. Further, this current study had a small sample size and the changes in the SUVs due to age and sex were not considered. The study also did not compare the trend in changes in the vertebral body among radio-chemotherapy patients. The diagnostic accuracy of the absence of metastasis warrants further verifi cation in the present study.

Conclusion
The difference in the bone metabolism of the lumbar vertebral body is caused by the variation in the horizontal direction of the vertebral body. The bone metabolism in the vertical direction of the lumbar vertebrae has more uniformity. As a quantitative imaging measure, the SUVs might require standardization with adequate reference data to minimize the variability in the participants.