Spiral Cone-beam Computed Tomography Research Articles

Morphometry of the cranial base and the cranial–cervical–mandibular system in young patients with type II, division 1 malocclusion, using tomographic cone beam

Aims:Traditionally, diagnosis and treatment planning of structural and three-dimensional anomalies have been performed using two-dimensional X-rays. Cone beam computed tomography (CBCT), the technology utilized in this study, allows creation of specialized images from the craniofacial region that provide more precise and reliable results. The growth of the cranial base, position and size of the cervical system, and the hyoid bone has an influence upon the morphogenesis and the growth of the maxillofacial complex. The data obtained through this current study offer a better understanding of the origin and manifestation of malocclusions, and will, therefore, offer a better therapeutic approach. The objective of the current study is to describe the measurements of the cranial base and the cranial–cervical–mandibular system in young patients with type II, division 1 malocclusion, using CBCT.Methodology:Twenty-four CBCT images were obtained for young patients with type II, division 1 malocclusion. The i-CAT Vision (Imaging Sciences International, Hatfield, PA, USA) was used to view the images. Linear and angular measurements were obtained in the mid-sagittal plane. Univariate and bivariate analyses, as well as a multivariate analysis of principal components, were conducted.Results:The only metric with a statistically significant difference regarding gender was S–N major in the male participants. The metrics SNA–SNB and SNPg are positively related and inversely proportional to the angles BA–S–N and PO–P McGregor. The inclination of the upper incisor showed an inverse relationship with the angles SNA–SNB and SNpg. The craniovertebral angle was diminished in the entire sample, and the variable that vertically relates the hyoid was independent of the other variables.Conclusions:After evaluating 24 images of young patients with type II, division 1 malocclusion using helical spiral CBCT, it was concluded that relationships exist between the cranial base structures, the structures that determine the sagittal position of the maxilla, mandible and chin, and the cervical vertebrae complex and hyoid bone.

Laplace operator based reconstruction algorithm for truncated spiral cone beam computed tomography

To reconstruct images from truncated projections collected along a spiral trajectory, the most common approach is to smoothly extrapolate each projection to suppress truncation artifacts. Based on the work of Dennerlein, a local reconstruction algorithm is developed for spiral cone beam computed tomography (CT), which does not need explicit projection extrapolation. This algorithm is a filtered-backprojection (FBP) format and contains three major steps: cosine weight, filtration, and backprojection. While the cosine weight and backprojection steps are the same as the classical Feldkamp - Davis - Kress (FDK) scheme, the filtering step contains two steps: Laplace filtering and Radon transform-based filtering. Numerical simulation results show that the proposed algorithm has a better performance than FDK algorithm for region-of-interest (ROI) reconstruction of spiral cone-beam CT.

Impact of the z-flying focal spot on resolution and artifact behavior for a 64-slice spiral CT scanner

The effect of the z-flying focal spot (zFFS) technology was evaluated by simulations and measurements with respect to resolution and artifact behavior for a 64-slice spiral cone-beam computed tomography (CT) scanner. The zFFS alternates between two z-positions of the X-ray focal spot, acquiring two slices per detector row, which results in double sampling in the z-direction. We implemented a modified reconstruction that is able to obtain images as they would be without zFFS. A delta phantom equipped with a thin gold disc was used to measure slice sensitivity profiles (SSP), and a high-contrast bar phantom was used to quantify the resolution in the x/z-plane with and without zFFS. The zFFS decreases the full width at half maximum (FWHM) of the SSPs by a factor of about 1.4. The double z-sampling allows the separation of 0.4 mm bars in the z-direction compared with 0.6 mm in the case without zFFS. The zFFS effectively reduces windmill artifacts in the reconstructed images while maintaining the transverse resolution, even at the largest available pitch value of 1.5.

Tilted plane Feldkamp type reconstruction algorithm for spiral cone beam CT

An approximate image reconstruction method for spiral cone beam computed tomography (CT), called tilted plane Feldkamp type reconstruction algorithm (TPFR), is presented in this paper, which extends Feldkamp cone beam reconstruction algorithm to deal with its inaccuracy and artifact problems caused by large cone angle. This is done by tilting the reconstructing planes to minimize the cone angle and optimally fit the spiral segment of the source. The tilted plane image reconstruction requires reforming the three-dimensional projection data set for the tilted plane and application of Feldkamp algorithm to the reformed data set. Analytical and computational results can show that the image reconstruction performance of the proposed TPFR algorithm is superior to that of the Feldkamp reconstruction algorithm in the image quality, volume coverage speed, maximum achievable pitch value, and slice sensitivity profiles. Moreover, it provides more accurate image reconstruction than the existing two-dimensional reconstruction algorithms.

A backprojection-filtration algorithm for nonstandard spiral cone-beam CT with an n-PI-window

For applications in bolus-chasing computed tomography (CT) angiography and electron-beam micro-CT, the backprojection-filtration (BPF) formula developed by Zou and Pan was recently generalized by Ye et al to reconstruct images from cone-beam data collected along a rather flexible scanning locus, including a nonstandard spiral. A major implication of the generalized BPF formula is that it can be applied for n-PI-window-based reconstruction in the nonstandard spiral scanning case. In this paper, we design an n-PI-window-based BPF algorithm, and report the numerical simulation results with the 3D Shepp–Logan phantom and Defrise disk phantom. The proposed BPF algorithm consists of three steps: cone-beam data differentiation, weighted backprojection and inverse Hilbert filtration. Our simulated results demonstrate the feasibility and merits of the proposed algorithm.

Three-dimensional CT with a modified C-arm image intensifier: feasibility.

A portable C arm was modified for cone-beam computed tomography (CT). This three-dimensional (3D) CT imaging system facilitated the acquisition of fluoroscopic images during a 190 degrees rotation and computed a 3D data cube (matrix, 256 x 256 x 256; scanning time, 100 seconds) with multiplanar image reformation. The high-contrast resolution, 0.9 line pairs per millimeter, was comparable; the low-contrast resolution, minimal; and the radiation dose, 60%-80% lower, as compared with these parameters at spiral CT. The normal anatomy of small joints could be depicted, and the osteosynthesis screws in the talus were correctly identified.

Advanced single-slice rebinning in cone-beam spiral CT.

To achieve higher volume coverage at improved z-resolution in computed tomography (CT), systems with a large number of detector rows are demanded. However, handling an increased number of detector rows, as compared to today's four-slice scanners, requires to accounting for the cone geometry of the beams. Many so-called cone-beam reconstruction algorithms have been proposed during the last decade. None met all the requirements of the medical spiral cone-beam CT in regard to the need for high image quality, low patient dose and low reconstruction times. We therefore propose an approximate cone-beam algorithm which uses virtual reconstruction planes tilted to optimally fit 180 degrees spiral segments, i.e., the advanced single-slice rebinning (ASSR) algorithm. Our algorithm is a modification of the single-slice rebinning algorithm proposed by Noo et al. [Phys. Med. Biol. 44, 561-570 (1999)] since we use tilted reconstruction slices instead of transaxial slices to approximate the spiral path. Theoretical considerations as well as the reconstruction of simulated phantom data in comparison to the gold standard 180 degrees LI (single-slice spiral CT) were carried out. Image artifacts, z-resolution as well as noise levels were evaluated for all simulated scanners. Even for a high number of detector rows the artifact level in the reconstructed images remains comparable to that of 180 degrees LI. Multiplanar reformations of the Defrise phantom show none of the typical cone-beam artifacts usually appearing when going to larger cone angles. Image noise as well as the shape of the respective slice sensitivity profiles are equivalent to the single-slice spiral reconstruction, z-resolution is slightly decreased. The ASSR has the potential to become a practical tool for medical spiral cone-beam CT. Its computational complexity lies in the order of standard single-slice CT and it allows to use available 2D backprojection hardware.