Image-derived input function from cardiac gated maximum a posteriori reconstructed PET images in mice

Abstract

Purpose: The purpose of this study was to determine if accurate image-derived input functions (IDIF) can be measured from cardiac gated positron emission tomography (PET) images reconstructed using ordered subset expectation maximization-maximum a posteriori (OSEM-MAP) without further correction.

Procedures: IDIFs from the left ventricle were measured from cardiac gated PET images reconstructed using OSEM-MAP with computed tomography (CT)-based attenuation correction for five C57/BL6 mice. The accuracy of the IDIF was tested against blood samples using Bland-Altman analysis.

Results: Image-derived blood radioactivity concentration values were not significantly different from sampled blood values at two late time points as determined by a paired t test (P = 0.97). Bland-Altman analysis revealed a mean difference of 0.06 μCi/ml (1%). Using kinetic analysis, the mean myocardial 2-deoxy-2-[(18)F]fluoro-D-glucose uptake rate constant based on the IDIF was comparable to values reported in the literature based on physical blood sampling.

Conclusions: Accurate IDIFs can be obtained non-invasively. Although reconstruction times are increased, no further spillover corrections are necessary for IDIFs derived from gated, OSEM-MAP reconstructed images with attenuation correction.

Fig. 1

Transaxial view of attenuation-corrected phantom images reconstructed with a) FBP and b) MAP and the recovery coefficient curves generated from them (c).

Fig. 2

Transverse FDG images of the mouse heart reconstructed using a) OSEM-MAP with cardiac gating, b) OSEM-MAP without cardiac gating, c) FBP with cardiac gating, and d) FBP without gating. Profiles through the transverse images are also shown. LVBP radioactivity concentrations are dependent on both image reconstruction algorithm and whether cardiac gating is employed. Cardiac gated images show an improved contrast between the blood pool and the myocardium in diastole compared to non-gated images. The FBP images shown appear to be noisier than the corresponding OSEM-MAP images despite the fact that both images have the same resolution. Only gated OSEM-MAP images can be used to accurately measure LVBP radioactivity concentration.

Fig. 3

Representative IDIFs for cardiac gated FBP and MAP reconstructions (black and gray curves, respectively) measured by a common ROI drawn in the region of the image corresponding to the LVBP. IDIF derived from non-gated FBP is shown (dotted line) to demonstrate the effect of not gating. CT-based attenuation and PV corrections were both applied. The square and circular boxes represent manually sampled blood activity concentrations taken at 43 and 56 minutes respectively, after FDG injection.

Fig. 4

Bland-Altman representation of the agreement between image-derived LVBP radioactivity (corrected for attenuation and partial volume effects) and physically sampled blood radioactivity in seven mice. Late time point samples (43 and 56 minutes post FDG injection) are represented by black diamonds and early time point samples (5 and 10 minutes post FDG injection) are represented by gray diamonds. The mean difference was −0.06 µCi/ml (solid line) and the lower and uppers limits of agreement were −0.22 and 0.34, respectively (dashed lines).