SPECT Blood Pool Imaging On Bone Scintigraphy Improves Diagnostic Yield Compared To Planar Imaging: Initial Experience
S K Gupta, N Rutherford, L Allen
blood pool, bone scan, scintigraphy, spect, tc-99m mdp
S K Gupta, N Rutherford, L Allen. SPECT Blood Pool Imaging On Bone Scintigraphy Improves Diagnostic Yield Compared To Planar Imaging: Initial Experience. The Internet Journal of Nuclear Medicine. 2013 Volume 6 Number 1.
Blood pool (BP) phase is of high importance as it improves the specificity of the bone scintigraphy. Traditionally planar images are obtained, which are difficult to interpret primarily due to poor target to background ratio and lack of anatomical details. In a small retrospective study, we evaluated the value of BP SPECT over planar imaging (n=39). SPECT not only identified lesions in 12/26 (46%) of the negative planar studies but also improved visualization (n=9), localization (n=9) and showed additional lesions (n=5) in the remainder. In this pilot study, SPECT improved the value of BP phase, potentially impacting the management.
Blood pool (BP) images are acquired within 10 minutes of tracer injection and reflect the alterations in the bone extracellular fluid from changes in capillary permeability and indicates an inflammatory component to the lesion (1). It helps differentiating various causes of uptake (2), improves the specificity of bone scan (3) (4) (5) and may identify soft tissue pathologies (6). However, traditional blood pool planar (BPP) images are difficult to interpret due to lower target to background ratio; overlying organ activity also precludes the satisfactory interpretation (5). Furthermore, relative lack of anatomical detail may lead to false positives reporting (7).
SPECT is known to improve sensitivity, specificity and diagnostic accuracy of delayed phase of bone scintigraphy (8). In our institution, blood pool SPECT (BPS) is performed on a case to case basis at the physician’s discretion. 800-1100 MBq of Tc-99m MDP is injected and BPP (two minutes/frame) and BPS (5 minutes acquisition) are obtained. If CT has been obtained in the delayed images, this may be fused with the BPS using semiautomated software registration algorithm on Xeleris-3 (GE healthcare) workstation.
In this small study, assessing the value of BPS, 39 consecutive bone scans (abdomen/pelvis, n=18; head and neck, n=11; and chest, n=10) were independently reviewed by two experienced nuclear medicine physicians (and 3rd physician in the event of discrepancy). All patients were non-oncological and had localized symptoms. BPP were negative in 26 but BPS identified lesions in 12 of these. Of the positive BPP studies, BPS improved visualization and localization in 9 each as well as showed additional lesions in 5 studies. Physicians felt BPS had potential impact in the management in 11 of all 39 studies.
A 91-year-old male underwent bone scintigraphy for evaluation of skull base osteomyelitis. The BPP images (A) are difficult to characterize. BPS (B), however, clearly shows hyperaemia in the soft tissue rather than associated with bone. This case illustrates potential value of BPS in identifying the soft tissue pathologies and its localization value when co-registered with CT.
A 50-years-old male with back pain following fall two weeks ago. BPS (B, C) clearly show T6 vertebral hyperaemia, which is difficult to appreciate on BPP (A) probably due to superimposed cardiac and mediastinal blood pool activities (Note the blood pool cardiac activity in the same horizontal plane). This is associated with avid delayed tracer uptake (D), consistent with recent fracture. This case illustrates improved sensitivity with BPS in identifying the hyperaemic lesions.
A 77-years-old female with neck pain was referred for bone scintigraphy. BPP images are normal (A) but BPS (B, C) shows focal mild hyperaemia at left C2/3 facet joint. The BPP was unable to identify the hyperaemic lesion due to neck vascular activities. There is avid delayed tracer uptake at this site (D) consistent with facet joint arthritis. This case illustrates potential value of BPS in areas of difficult anatomy.
A 68-years-old female with recent onset sacral region pains. (Not a current study patient) BPP shows symmetrical hyperaemia in the SI joints bilaterally (A,B). BPS confirmed hyperaemia, in fact, to be localized to the sacral ala bilaterally with sparing of SI joints. (C) Delayed images (D, E) and MRI (Images not shown) confirmed presence of insufficiency fracture rather than sacroiliitis. This case illustrates the excellent localization value of BPS when co-registered with CT.
Discussion and Conclusion
Although this is a smaller study, BPS does appear to improve the value of the early phase of bone scintigraphy. Future studies, however, will be needed to further elaborate the impact on the management.