Deriving Cardiac Reference Ranges at 3.0Tesla in Healthy Volunteers

Imaging societies recommend that each MRI scanner has a locally-derived reference range for tissue characteristics, notably the longitudinal (T1) and transverse (T2) myocardial relaxation times, measured in milliseconds [16].

T1 reference values vary according to the magnetic field strength of the MRI scanner. T1 and T2 times (ms) are expectedly higher at 3.0T compared to 1.5T, in line with results obtained when working with the Siemens VERIO scanner based at the BHF Glasgow Cardiovascular Research Centre [17]. T2 values for 3.0T are, generally, not so well described and are known to vary between different manufacturers and systems.

A consensus statement by Society for Cardiovascular Magnetic Resonance (SCMR) endorsed by the European Association for Cardiovascular Imaging (EACVI) states that "Reference ranges should be generated from data sets that were acquired, processed, and analyzed in the same way as the intended application, with the upper and lower range of normal defined by the mean plus and minus 2 standard deviations of the normal data, respectively."[16] Myocardial blood flow measurements for both stress and rest are also distinct for individual scanners, especially at 3.0T. In fact, a number of centres have derived site specific and magnet specific reference ranges from healthy volunteers including 1)Stockholm, Sweden, 1.5T Siemens Avanto, 3.4 ± 0.7 ml/min/g [18] 2) Barts (London, UK) 3.0T Siemens Prisma, 3.00 +/-0.76 ml/g/min (unpublished data) and 3) Leeds, UK: 3.0T Siemens Prisma 2.89 ± 0.56 ml/g/min [19], 1.5T Philips Intera, 4.50 ± 0.91 ml/min/g[20] and studies are ongoing in sites such as Oxford (https://www.ouh.nhs.uk/research/patients/trials/stress-mri.aspx) . As can be seen, there is a wide spread of values and local reference ranges are urgently required (defined as stress MBF <2 standard deviations from the mean in healthy volunteers). These measurements are not yet available for the 3.0T Prisma scanner at the Institute of Clinical Excellence (ICE), Queen Elizabeth University Hospital (QEUH). These values are essential to identify what is abnormal for people living in the west of Scotland.