Intrinsic respiratory gating in small-animal CT

Abstract

Gating in small-animal CT imaging can compensate artefacts caused by physiological motion during scanning. However, all published gating approaches for small animals rely on additional hardware to derive the gating signals. In contrast, in this study a novel method of intrinsic respiratory gating of rodents was developed and tested for mice (n=5), rats (n=5) and rabbits (n=2) in a flat-panel cone-beam CT system. In a consensus read image quality was compared with that of non-gated and retrospective extrinsically gated scans performed using a pneumatic cushion. In comparison to non-gated images, image quality improved significantly using intrinsic and extrinsic gating. Delineation of diaphragm and lung structure improved in all animals. Image quality of intrinsically gated CT was judged to be equivalent to extrinsically gated ones. Additionally 4D datasets were calculated using both gating methods. Values for expiratory, inspiratory and tidal lung volumes determined with the two gating methods were comparable and correlated well with values known from the literature. We could show that intrinsic respiratory gating in rodents makes additional gating hardware and preparatory efforts superfluous. This method improves image quality and allows derivation of functional data. Therefore it bears the potential to find wide applications in small-animal CT imaging.

Intrinsic Gating for Small-Animal Computed Tomography

“…However, taking into account previous dose measurements on mouse phantoms, 28,29 the scan time, and our scan parameters, only a dose of Ϸ90 mGy was delivered to the animal. This dose stays within the limits set in previous studies [5][6][7][8][9][10] with prospective or retrospective gating and cannot be expected to significantly affect the health of rodents. In general, dose usage is better in prospective methods, because all projections contribute to image reconstruction.…”

“…Its main features were a flat-panel detector and a modified x-ray tube, both mounted on a multislice CT gantry. 9,10,13 The flat-panel detector (PaxScan 4030CB, Varian Medical Systems) used by this prototype scanner consisted of 2048ϫ1536 detector pixels over an active area of 40ϫ30 cm 2 , resulting in a pixel size of 194 2 m 2 . For this experiment, the active detector area was limited to 192 lines in the z direction and 1024 rows in the x-y direction to increase the frame rate.…”

“…Both prospective [5][6][7] and retrospective 8 -10 methods for respiratory and cardiac gating have been described, and their benefit for image analysis has been demonstrated. [7][8][9][10] Regardless of whether they are retrospective or prospective, all gating methods currently in use in small-animal CT imaging depend on ECG to derive a gating reference signal. In addition, heart movement attributable to respiration must either be suppressed via intubation or detected by a pneumatic cushion and taken into consideration.…”

“…Self-gating (synonymous with image-based, intrinsic, or raw data-based gating) in small-animal CT, in which the gating information is taken directly from the acquired projection data, has so far only been demonstrated for respiratory motion imaging. 10 Small-animal MRI can also be used to acquire self-gated 4D imaging of the heart. A 1D projection-based self-gating method has been already demonstrated for cardiac MRI with radial k-space acquisition.…”

Airway remodeling in a mouse asthma model assessed by in-vivo respiratory-gated micro-computed tomography

“…Mice were anaesthetised using an intraperitoneal injection of both 50 μg/g ketamine (Panpharma, Fougeres, France) and 5 μg/g xylazine (Sigma-Aldrich, Saint-Quentin-Fallavier, France). They were then challenged intranasally with 500 μg of ovalbumin on days 14,27,28,29,47, 61, 73, 74 and 75 as described by Henderson et al [9]. The control group (n=6) received normal saline intraperitoneally or intranasally on the same days.…”