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xSPECT Imaging in a Patient with Diffuse Skeletal Metastases

Quantification of tracer uptake within lumbar vertebrae

Author: Partha Ghosh, MD and Patrick Sorger, CNMT, Siemens Healthcare, Hoffman Estates, Ill., USA

Case study data provided by Ludwig-Maximilians University, Munich, Germany

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Fig. 1: 99mTc MDP planar bone study.

History
A 70-year-old woman with history of breast carcinoma treated with surgery and chemotherapy underwent 99mTc MDP bone scintigraphy for routine follow-up. A planar bone scan was performed initially 3 hours after IV injection of 18.5 mCi (685 MBq) of 99mTc MDP. Patient height and weight:1.65 meters/5'5" and 57 kg/125.6 lbs.
Planar 99mTc MDP bone study (Figure 1) shows increased uptake in the left proximal humerus (long arrow), which was suspicious for metastases. A small focal area of increased uptake in the cervical and lower lumbar vertebrae (short arrow) appears to be related to degenerative changes. Thoracic and lumbar vertebral uptake seems normal along with that of extremities, ribs and pelvis. Both kidneys are well visualized.
A SPECT/CT study of the lumbar vertebrae was performed following the planar scan to better characterize the lumbar vertebral uptake. SPECT data was initially reconstructed using OSEM3D (Flash3D) together with CT attenuation and scatter correction. SPECT and CT data were also used to generate xSPECT1,2 bone images. xSPECT Bone1 technology is an application context-based solution, whereby tissue boundaries are extracted from CT via a linear-attenuation-coefficient-based segmentation in order to improve image resolution.
 

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Fig. 2: Conventional SPECT/CT and xSPECT slices through the lumbar vertebrae
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Fig. 3: CT and xSPECT images of lumbar vertebrae

Examination Protocol
Scanner: SymbiaTM with xSPECT Technology
Dose: 18.5 mCi /685 MBq of 99mTc MDP
Scan Delay: 3 hour post injection
Parameters: 32 frames, 25 sec/frame
CT: 130 kVp, 90 eff mAs, 3 mm slice

 

Analysis
xSPECT shows higher intensity of uptake secondary to facet arthropathy in the right facet joint in L5 vertebrae com¬pared to conventional SPECT/CT (Figure 2), as well as clear and sharp delineation of lamina, spinous process and spinal canal. Uptake of tracer in the lumbar vertebrae appears uniform.
Visual evaluation of the CT and fused images (Figure 3), however, show a different clinical picture. CT shows diffuse sclerosis involving all the lumbar vertebrae, including the body of the sacrum and the lamina and spinous processes. Such diffuse sclerosis could potentially reflect diffuse osseous metastases. Visually the 99mTc MDP uptake in the sclerotic vertebrae appear uniform without any focal increase. Visualization of kidneys and bladder activity exclude a "superscan" appearance.
Using xSPECT-based quantification1,2 of SPECT tracer concentration in Bq/ml and using injected dose and patient height and weight information, the standard uptake value (SUV) of individual voxels, as well as volumes, could be calculated (Figure 4).
 

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Fig. 4: Quantitative evaluation of 99mTc MDP absolute tracer concentration within the lumbar vertebral body in kB/ml and calculated vertebral SUV2 enabled by xSPECT technology

Comments
Absolute quantification of tracer concentration in the lumbar vertebrae with the new modality, xSPECT, shows 157 kBq/ml of 99mTc MDP in the center of the body of L3 vertebrae (arrow) with an SUV average (SUVavg) of 14.95, which is approximately 2 times higher than that of normal (SUV average of 7.02).2,3 This high SUV within the lumbar vertebrae along with a diffuse sclerosis on CT is reflective of diffuse osseous metastases. The planar bone study did not show diffuse vertebral hypermetabolism and both kidneys were visualized, excluding a superscan appearance. This can be explained by response of the diffuse vertebral metastases to chemotherapy, but with persistent higher level of vertebral metabolism, due to the increased bone turnover within the sclerotic component, as evident in the increased tracer concentration and SUV within the vertebrae.

Measurements using xSPECT data in lumbar vertebrae of 8 normal female patients2,3 (average 64 years of age; injected dose 537 +/- 82 MBq) yielded average bone tracer activity concentration (AC) of 56.70 +/- 17.21 kBq/ml and average SUV of 7.02 +/- 1.67.2

  1. Symbia Intevo, xSPECT, xSPECT Bone and xSPECT Quant are not commercially available in all countries. Due to regulatory reasons their future availability cannot be guaranteed. Please contact your local Siemens organization for further details.
  2. These are preliminary quantitative values defined on prototype system with prototype calibration, and are based on research. There can be no guarantee that customers will achieve the same results. Final results may vary.
  3. Cachovan, Michal; Vija, A. Hans.; Hornegger, Joachim; Kuwert, Torsten. "Quantitative bone SPECT with a novel multimodal reconstruction", J. Nucl. Med. Meeting Abstracts, 2013; Vol.TBD
     

 

Date: 2013-06-13


Molecular Imaging - Case Studies

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