Gated SPET quantification of small hearts: mathematical simulation and clinical application

Quantification of gated single-photon emission tomography (SPET) in small h earts has been considered to be inaccurate. To evaluate the validity of gat ed SPET in a small chamber volume, mathematical simulation and clinical app lication to paediatric patients were performed. Myocardium with various cha mber sizes from 14 ml to 326 ml was generated assuming an arbitrary resolut ion (6.9-15.7 mm in full-width at half-maximum), noise and zooming factors. The cut-off frequency of the Butterworth filter for preprocessing was vari ed from 0.16 to 0.63 cycles/cm. The chamber volume was calculated by quanti tative gated SPET software (QGS), The patients, aged 2 months to 19 years ( n = 27), were studied by gated technetium-99m methoxyisobutylisonitrile or tetrofosmin SPET. Image magnification as large as possible was performed du ring data acquisition to include the whole chest using 1.25-2.0 zooming. Ba sed on the simulation study, an underestimation of the chamber volume occur red below a volume of 100 ml. The degree of underestimation for a 37-ml vol ume was 49% without zooming, but it improved to 3% with 2x zooming. Filters with a higher cut-off frequency, better system resolution and hardware zoo ming during acquisition improved quantitative accuracy in small hearts. For the subjects under 7 years old (n = 7), quantification of volume and eject ion fraction (EF) was possible in 72% of the patients. In those over 7 year s old, gated SPET quantification was feasible in all cases. The correlation between gated SPET end-diastolic volume (SPET EDV) and both echocardiograp hic end-diastolic dimension (EDD) and echocardiographic EDV was good (r = 0 .84 between SPET EDV and echo EDD, r = 0.85 between SPET EDV and echo EDV, P < 0.0001 for both). The correlation between gated SPET EF and both echoca rdiographic fractional shortening (FS) and echocardiographic EF was fair (r = 0.69 between SPET EF and echo FS, r = 0.72 between SPET EF and echo EF, P < 0.8001 for both). In conclusion, quantification of gated SPET of small hearts can be improved by means of a SPET filter with a high cut-off freque ncy, high system resolution and appropriate zooming. Gated SPET should be a ttempted not only in patients with small hearts but also in paediatric pati ents.