Abstract
Respiratory-induced organ displacement during image acquisition can produce motion artifacts and variation in spatial localization of an organ in diagnostic computed tomography (CT) examinations. The purpose of this prospective study was to quantify respiratory-induced abdominal organ displacement in dorsal and ventral recumbency using five normal dogs. All dogs underwent CT examinations using 64 multidetector row CT (64-MDCT). A "3-dimensional (3D) apneic CT exam" of the abdomen was acquired followed by a "4-dimensional (4D) ventilated CT exam." The liver, pancreas, both kidneys, both medial iliac lymph nodes, and urinary bladder were delineated on the 3D-apneic examination and the organ outlines were compared to the maximum alteration in organ position in the 4D-ventilated examination. Displacement was measured in dorsal-to-ventral (DV), right-to-left (RL), and cranial-to-caudal (CC) directions. Respiratory-induced displacement of canine abdominal organs was not predictable and showed large variability in the three directions evaluated. For most canine abdominal organs, dorsal recumbency provided overall the least amount of displacement among all directions evaluated except for liver and urinary bladder. For liver, a large variability was found for all directions and a statistically significant difference was found only in the RL direction with ventral recumbency exhibiting less displacement (P = 0.0099). For the urinary bladder, ventral recumbency also provided less displacement but this was statistically significant only in the RL direction (P < 0.0001). Findings from this study indicated that dorsal recumbency may be preferred for minimizing respiratory motion artifacts in whole abdomen studies, but ventral recumbency may be preferred for liver and urinary bladder studies when respiration cannot be controlled.
Highlights
Respiratory-induced organ displacement during image acquisition can produce motion artifacts and variation in spatial localization of an organ in diagnostic computed tomography (CT) exams
Dorsal recumbency resulted in significantly less DV (P = 0.0005) and RL (P = 0.0371) displacement compared to ventral recumbency (Table 2, Figure 4a)
Our methodology for measuring abdominal structure displacement was similar to previous human studies evaluating organ displacement and to a recent canine study evaluating intrafractional motion of the prostate.[2,3,5,6]
Summary
Respiratory-induced organ displacement during image acquisition can produce motion artifacts and variation in spatial localization of an organ in diagnostic computed tomography (CT) exams. Motion artifact can appear as blurred organ margins or transposition of the plane of an organ between slices in the transverse plane and stair step artifact when evaluating dorsal and sagittal plane reconstructions.[1] The increasing use of multi-slice CT units in veterinary diagnostic imaging enables increasingly rapid acquisition of abdominal exams that can be kept mostly free of respiratory artifact by an induced short apnea. Many institutions operate or acquire single detector-row CT units that require extended apnea to avoid respiratory-induced motion artifacts, which may not be feasible in a given patient. This recommendation is currently not based on scientific evidence in veterinary medicine
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