Estimation and correction of respiratory motion in pediatric renal SPECT through a data-driven center-of-mass method

Respiratory motion is known to cause blurring in Single-Photon Emission Computed Tomography (SPECT) images which can mask or mimic disease. Pediatric imaging with ^99mTc-labeled dimercaptosuccinic acid (DMSA) is used to assess cortical defects in kidneys and may be especially susceptible to artifacts introduced by respiratory motion due to the thin kidney cortices and small kidney volumes seen in many pediatric patients.

The purpose of this study was to assess a data-driven method to estimate respiratory motion signals in pediatric ^99mTc-DMSA renal SPECT and to evaluate the impact of respiratory motion correction on image quality.

Listmode ^99mTc-DMSA SPECT data were acquired for 77 pediatric patients aged from 6 weeks to 20 years. The data were binned into 100 ms temporal frames and forward-projected kidney masks were used in determining the axial center-of-mass (aCOM) of counts in each temporal frame as a surrogate renal respiratory motion signal for each patient. Amplitudes of respiratory motion in the lateral, anterior-posterior and axial (superior-inferior) axes were determined using a rigid-body six-degree-of-freedom intensity-based registration method and evaluated as a function of patient weight. Welch t-tests were performed to compare the respiratory motion amplitudes of male and female patients. Subsequently, a rigid-body 6-degree-of-freedom respiratory motion correction was applied during reconstruction and the images were quantitatively assessed for improvement in contrast and sharpness.

Renal respiratory motion surrogate signals were estimated for 69 patients, after eight were removed due to gross body motion. Axial, lateral and anterior-posterior translational renal respiratory motion amplitudes were all found to positively correlate with patient weight, with lateral motion showing the strongest correlation. Respiratory motion was largest in the axial direction where it ranged from (2.19  $\pm$  0.48) mm for the patients under 7 kg to (6.96  $\pm$  3.07) mm for patients over 60 kg. No significant differences were found in axial or anterior-posterior renal respiratory motion between male and female patients, but lateral motion was slightly lower for females. Quantitative assessment of reconstructed images showed that respiratory motion correction improved contrast and sharpness as a function of estimated amplitude of axial respiratory motion, suggesting a threshold where motion correction becomes beneficial.

A data-driven respiratory motion estimation method found significant positive correlation in renal motion amplitudes and weight for pediatric DMSA SPECT studies. The derived respiratory signals were used to perform rigid-body respiratory motion correction during reconstruction. The renal respiratory motion correction reduced cortical blurring and improved contrast in some patients, generally those with the largest estimated motion, highlighting potential for this method to improve diagnostic accuracy.