Micro‐CT with respiratory and cardiac gating

Abstract

Cardiopulmonary imaging in rodents using micro-computed tomography (CT) is a challenging task due to both cardiac and pulmonary motion and the limited fluence rate available from micro-focus x-ray tubes of most commercial systems. Successful imaging in the mouse requires recognition of both the spatial and temporal scales and their impact on the required fluence rate. Smaller voxels require an increase in the total number of photons (integrated fluence) used in the reconstructed image for constant signal-to-noise ratio. The faster heart rates require shorter exposures to minimize cardiac motion blur imposing even higher demands on the fluence rate. We describe a system with fixed tube/detector and with a rotating specimen. A large focal spot x-ray tube capable of producing high fluence rates with short exposure times was used. The geometry is optimized to match focal spot blur with detector pitch and the resolution limits imposed by the reproducibility of gating. Thus, it is possible to achieve isotropic spatial resolution of 100 μm with a fluence rate at the detector 250 times that of a conventional cone beam micro-CT system with rotating detector and microfocal x-ray tube. Motion is minimized for any single projection with 10 ms exposures that are synchronized to both cardiac and breathing motion. System performance was validated in vivo by studies of the cardiopulmonary structures in C57BL/6 mice, demonstrating the value of motion integration with a bright x-ray source.

Three‐dimensional magnetic resonance microscopy of pulmonary solitary tumors in transgenic mice

“…On the selected section, a 3D GRE sequence was performed again using the cardiac-respiratory triggering system in which MR signal was collected once over a cardiac cycle at a synchronized phase of the end-systolic cardiac and endexpiratory phases. TR and TE were the same as those used in experiment I, and the other scan parameters were: matrix size ϭ 128 ϫ 128 ϫ 100 (zero-filled to 128 ϫ 128 ϫ 128) and NEX ϭ 1, affording a (200 m) 3 isotropic voxel. The total scan time was approximately 1.1 hr.…”

“…The involvement of high radiation may affect intrinsic or exogenous biological activity, particularly for repeated imaging in a longitudinal study. In addition, implementation of respiratory and cardiac gating, which is a requisite technology for in vivo thoracic imaging of small animals, is generally limited except in special cases (3). In contrast, MRI is free of ionizing radiation, and is able to provide detailed information simultaneously on the anatomy and function of both soft and hard tissues (4,5) in vivo in laboratory animals.…”

In Vivo mouse imaging and spectroscopy in drug discovery

“…Micro-CT systems providing high-resolution images ($50 mm) and rapid data acquisition (typically 5-30 min) are emerging as a cost-effective means for detecting soft-tissue structures, skeletal abnormalities, and tumors in small animals (24,(45)(46)(47). The use of iodinated contrast agents enhances the weak endogenous contrast between different soft tissues.…”

“…Micro-CT provides the necessary spatial resolution of 3D images of the intact thoracic contents (45,51) (Fig. 7).…”

High-Resolution CT for Small-Animal Imaging Research

“…This produces a set of projections with a constant angular step, resulting in reconstructed images that are free of streaking artifacts. However, because of the time spent waiting for the coincidence of cardiac and respiratory events, the scan time can take as long as 1 h to cover 10 different phases of the cardiac cycle (Badea et al, 2004).…”