Application of post reconstruction dual respiratory and cardiac motion compensation for 4D high-resolution small animal myocardial SPECT

We investigated the performance of a post reconstruction dual respiratory and cardiac (R&C) motion compensation method for improved image quality of 4D cardiac gated small animal myocardial perfusion (MP) SPECT images. A normal mouse was injected with ∼8 mCi of Tc-99m sestamibi, anesthetized, fitted with ECG leads for cardiac gating signal acquisition, and placed on top of a pressure gauge bellow for respiratory motion measurements. A 2-hour list-mode dataset was acquired using a MILab small animal SPECT system fitted with a multi-pinhole collimator with 0.4 mm resolution in 5-minute sections. They were subsequently sorted for different acquisition times and reconstructed using a vendor provided OS-EM algorithm with simultaneous 6 respiratory and 8 cardiac equal-time gates over each motion cycle. Using a group-wise B-spline non-rigid image-based registration method, the deformation fields of the respiratory motion (respiratory motion) were estimated and applied to each cardiac phase for respiratory motion correction. Then, the respiratory motion compensated cardiac gated SPECT images were similarly used to estimate cardiac motion (cardiac motion) and later transformed to a reference frame and summed. Finally, the reference frame was inverse-transformed using the estimated cardiac motion to each of the 8 cardiac frames. The cardiac gated images with dual R&C motion compensation were compared to those without correction but with post-smoothing filter. The results showed the dual R&C motion compensation significantly reduced image noise level. At the same time, the image resolution was improved by 10% to 40% depending on the different acquisition times when compared with that obtained without motion compensation at the same image noise level. We conclude that dual R&C motion compensation provides significant reduction of noise level in 4D cardiac gated small animal MP SPECT images with minimum degradation of resolution. The improved image quality can be traded for reduction of acquisition time or radiation dose to the animal.