Maintaining image quality in VQ SPECT

Author(s): Matthew Memmott, Dr Sivakumar Muthu

Hospital: Central Manchester University Hospitals

Reference: RAD Magazine, 43, 507, 17-18


During 2015 and 2016, 50,696 admissions for acute pulmonary embolism were reported in the UK alone, resulting in an incidence of around 0.8 per 1,000 population. Just under 10% of these cases were in patients aged 40 or under; a cohort with greater than the reported 0.005% per mSv average lifetime cancer risk. While VQ scintigraphy is generally considered a low dose procedure (up to 2.8mSv for the maximum ARSAC diagnostic reference level (DRL) for 99mTc based radionuclides), the requirement for dose optimisation while maintaining diagnostic image quality still remains.

Despite first appearing in the literature just before the publication of the widely implemented PIOPED criteria for interpretation of planar lung imaging, SPECT imaging for pulmonary embolism has only relatively recently become routine practice. VQ SPECT is now explicitly mentioned in NICE guidelines (CG144) as an alternative to CT pulmonary angiography for patients who have an allergy to contrast media, renal impairment or whose risk from irradiation is high. This is supported by a recent meta-analysis that demonstrated no significant difference between the diagnostic accuracy of VQ SPECT and CTPA; with the former being more efficient in terms of radiation dose and the latter only in terms of financial cost.

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