Does quantification have a role to play in the future of bone SPECT?

Abstract

Routinely, there is a visual basis to nuclear medicine reporting: a reporter subjectively places a patient's condition into one of multiple discrete classes based on what they see. The addition of a quantitative result, such as a standardised uptake value (SUV), would provide a numerical insight into the nature of uptake, delivering greater objectivity, and perhaps improved patient management.For bone scintigraphy in particular quantification could increase the accuracy of diagnosis by helping to differentiate normal from abnormal uptake. Access to quantitative data might also enhance our ability to characterise lesions, stratify and monitor patients' conditions, and perform reliable dosimetry for radionuclide therapies. But is there enough evidence to suggest that we, as a community, should be making more effort to implement quantitative bone SPECT in routine clinical practice?We carried out multiple queries through the PubMed search engine to facilitate a cross-sectional review of the current status of bone SPECT quantification. Highly cited papers were assessed in more focus to scrutinise their conclusions.An increasing number of authors are reporting findings in terms of metrics such as SUV_max. Although interest in the field in general remains high, the rate of clinical implementation of quantitative bone SPECT remains slow and there is a significant amount of validation required before we get carried away.

Keywords: Bone scan; Nuclear medicine; Quantitative SPECT; SUV; Skeletal scintigraphy.

Fig. 1

a–f According to one study, no statistically significant systematic differences were observed between results produced using planar whole-body bone scans, SPECT-CT, and PET-CT on newly diagnosed, high-risk prostate cancer (Fonager et al. 2017). But planar whole-body bone scans can lead to misclassifications. Fonager et al. described the following: ‘Anterior and posterior projections of the bone scan (a) were interpreted as non-metastatic on the dichotomous scale (with equivocal uptake in the pelvic region noted on the three-point scale). Both SPECT (b) and NaF PET (c) showed metastatic lesions on the maximum intensity projection images (long and short black arrows).’ (Images courtesy of e-Century PublishingCorporation, Wisconsin, USA)

Fig. 2

Kim et al. demonstrated a strong correlation between quantitative bone SPECT results and results from visual grading for patients with osteoarthritis of the knee (Kim et al. 2017). (Permission to reuse this figure was reached in agreement with Elsevier on 28th March 2019)

Fig. 3

The results from Literature Search 1 illustrate a sustained rise in the number of general quantitative SPECT studies (a); the results from Literature Search 2 demonstrate that published data on quantitative bone scintigraphy is sparse (b). (Data reflect the numbers of papers published annually until the end of 2018)

Fig. 4

a–c SUV_max normalised to lean body mass has been reported as the best metric of osseous uptake for reducing patient variance (Kaneta et al. 2016). Labels on bottom-axes denote vertebrae. (Figure courtesy of e-Century PublishingCorporation, Wisconsin, USA)

Fig. 5

A local case study. Using GE’s Q.Volumetrix MI (GE Healthcare) the SUV_max at the confirmed site of fusion in the lumbar spine was found to be 28.7 (SUV_mean = 15.4), which sits comfortably above Kuji et al.’s normal range (but also within the range derived for metastases) (Kuji et al. 2017). The SUV_mean across all CT-segmented bone in the field of view was 3.48, which was lower than expected according to Kaneta et al.’s normal SUV_mean range (4.4 ± 0.5). Automated thresholding was employed to delineate the site. Is any of this more useful than visual interpretation? The quantitative result at the fusion site might have supplemented visual interpretation with something of prognostic value. In addition, comparisons could have been made upon follow-up SPECT-CT, enabling better ongoing characterisation of pain generation. Clearly, however, precision is still lacking

Fig. 6

Images of an 18-year-old male’s right leg produced with xSPECT Quant™ and xSPECT Bone™ (Siemens Healthineers), containing a giant cell tumour in the proximal fibula. Uptake in proximal tibio-fibular joint was concluded as normal as it was mild and reactive and no erosion could be seen. Siemens claim that xSPECT Bone™ offers improved image quality and lesion localisation through sharper edge delineation. But is there enough evidence to assume it can be routinely called upon to perform accurate and reproducible quantification to support important clinical decisions? (Images courtesy of Siemens Healthineers, Erlangen, Germany)

Fig. 7

Absolute quantification is possible with Hybrid Recon™ (Hermes Medical Solutions). An SUV_max of 12.05 and an SUV_peak of 11.40 were generated in the delineated area of this patient’s lumbar spine. (Images courtesy of Hermes Medical Solutions, London, UK)