Radiation Dose Of CT Scan Research Articles

Low dose CT image statistical reconstruction algorithms based on discrete shearlet

Reducing number of projection angles and lowering current intensity of X-ray tube are two common ways for reducing CT dose. Though reduced radiation dose of CT scan can lower damage to human bodies, Few number of projection angles will result in incomplete projection data while lowering tube current intensity a declined signal to noise ratio of projection data. In this paper, two statistical methods based on sparsity constraint in shearlet domain for low-dose CT image were proposed to solve the above problems. For the limited angle scanned reconstruction, sparse representation of intermediate images in shearlet domain is added into the objective function as a regularization item by means of Augmented Lagrangian method so as to narrow down solution space. For the low X-ray tube scanned reconstruction, a penalized weighted least-squares (PWLS) approach based on discrete shearlet was introduced to improve the performance of resisting noise in sinogram. And then reconstruct CT images by Filtered Back-Projection method. According to experimental data, both of the two approaches can get high-quality images when projection data is far from meeting conditions of completeness or the signal to noise ratio of projection data declines sharply. The proposed algorithms can be used for attaining reconstructed images that clearly keep structural details when the radiation dose is decreased to 10% or even lower degrees.

TU‐EF‐204‐07: Add Tube Current Modulation to a Low Dose Simulation Tool for CT Systems

Purpose:We extended the capabilities of a low dose simulation tool to model Tube‐Current Modulation (TCM). TCM is widely used in clinical practice to reduce radiation dose in CT scans. We expect the tool to be valuable for various clinical applications (e.g., optimize protocols, compare reconstruction techniques and evaluate TCM methods).Methods:The tube current is input as a function of z location, instead of a fixed value. Starting from the line integrals of a scan, a new Poisson noise realization at a lower dose is generated for each view. To validate the new functionality, we compared simulated scans with real scans in image space.Results:First we assessed noise in the difference between the low‐dose simulations and the original high‐dose scan. When the simulated tube current is a step function of z location, the noise at each segment matches the noise of 3 separate constant‐tube‐current‐simulations. Secondly, with a phantom that forces TCM, we compared a low‐dose simulation with an equivalent real low‐dose scan. The mean CT number of the simulated scan and the real low‐dose scan were 137.7±0.6 and 137.8±0.5 respectively. Furthermore, with 240 ROIs, the noise of the simulated scan and the real low‐dose scan were 24.03±0.45 and 23.99±0.43 respectively, and they were not statistically different (2‐sample t‐test, p‐value=0.28). The facts that the noise reflected the trend of the TCM curve, and that the absolute noise measurements were not statistically different validated the TCM function.Conclusion:We successfully added tube‐current modulation functionality in an existing low dose simulation tool. We demonstrated that the noise reflected an input tube‐current modulation curve. In addition, we verified that the noise and mean CT number of our simulation agreed with a real low dose scan.The authors are all employees of Philips. Yijun Ding is also supported by NIBIB P41EB002035 and NIBIB R01EB000803.

GPU-based Iterative CT Reconstruction via Edge-preserving Total Variation Regula

High radiation dose in CT scans increases a lifetime risk of cancer and is always a major concern. Two possible ways to decrease the dose are using fewer projections for reconstruction or lower the X-ray tube current. The former may require new hardware while the latter can be readily implemented. However, conventional filtered backprojection (FBP) reconstruction algorithms failed in both ways. Recently, iterative reconstruction algorithm with Total Variation (TV) regularization has been developed to reduce the imaging dose.

TU-B-201B-03: CT Reconstruction from Undersampled Projection Data Via Edge-Preserving Total Variation Regularization

Purpose: High radiation dose in CT scans increases a lifetime risk of cancer and is always a major concern. Recently, iterative reconstruction algorithm with Total Variation (TV) regularization has been developed to reconstructCTimages from highly undersampled data in order to reduce the imaging dose. Nonetheless, CTimagesreconstructed in this approach are sometimes over‐smoothed and edge information is lost. In this work, we developed an iterative CTreconstruction algorithm with edge preserving TV regularization to accurately reconstructCTimages from highly undersampled data. Methods and Material: The CTimage is reconstructed by minimizing TV norm under a constraint posed by few X‐ray projections. To avoid over‐smoothed edge, an edge‐preserving penalty was proposed and added to the TV norm. We tested our reconstruction algorithm on 4 cases, namely, Shepp‐Logan head phantom, NCAT phantom at thorax region, a real patient head case and a real patient lung case. The reconstruction accuracy was evaluated using relative error and edge correlation coefficient. Conventional FDK filtered backprojection algorithm and conventional TV regularization method without edge preserving term were also studied for comparison purpose. Results: It is found that 30 equi‐angle projections are enough for reconstructing the CTimages in phantom experiments and 40 projections for real patient experiments. Our approach outperforms the FDK algorithm and the conventional TV algorithm in terms of the relative error and the edge correlation coefficient in all the four test cases. In particular, the reconstructed images using our approach contain less noise and sharp edges. Conclusion: The edge‐preserving TV performs better in CTimages reconstruction. About 30∼40 X‐ray projections are enough to accurately reconstruct the CTimages, which implies a potential radiation dose reduction by about 20 times.

Computed Tomography in Total coronary Occlusions (CTTO Registry): radiation exposure and predictors of successful percutaneous intervention

There is no mention in the current "appropriateness criteria for CTCA" of the need of CTCA investigation prior to an attempt at recanalisation of a CTO. To define better the role of CTCA in the treatment of patients with CTOs, we performed CTCA in a consecutive cohort of eligible patients who were scheduled for percutaneous recanalisation of a CTO. Symptomatic patients due to a CTO suitable for percutaneous treatment were included. One hundred and thirty-nine (142 CTOs) patients were studied. Overall success rate was 62.7%. By CTCA, the occlusion length was 24.9 +/- 18.3 vs. 30.7 +/- 20.7 mm in successful and failed cases (p = 0.1), but the frequency of patients with an occlusion length >15 mm was different, i.e., 63.2% vs. 82.7%, respectively (p = 0.02). Severe calcification, (> 50% CSA) was more prevalent in failed cases (54.7% vs. 35.9%, p = 0.03). Calcification at the entry of the occlusion was present in 58.5% of the failures vs. 41.6% of the successful cases (p = 0.04), while calcium at the exit was not different. The length of calcification was 8.5 +/- 8.4 vs. 5.5 +/- 6.6 mm in the failed and successful cases respectively (p = 0.027). By multivariable analysis, the only independent predictor of procedural success was the absence of severe calcification as defined by CTCA. The mean effective radiation dose of the PCI was 39.3 +/- 30.1 mSv. The mean effective radiation dose of CT scan was 22.4 mSv: 19.2 +/- 6.5 mSv for contrast-enhanced scan, 3.2 +/- 1.7 mSv for calcium scoring scan. More severe calcified patterns, as assessed by CTCA, are seen in failed cases. The radiation exposure during a CT scan prior to a CTO PCI is considerable, and further studies are required to determine whether this extra diagnostic study is warranted.

Welchen Stellenwert hat das Ganzkörper-Spiral-CT in der Primärdiagnostik polytraumatisierter Kinder?

Whole body spiral CT scans have become a routine method in the radiological imaging of severely injured patients in emergency rooms of an increasing number of hospitals. The routine use of CT scans is, however, still discussed controversially, especially with regard to its use in children. This is mainly due to the reportedly higher level of exposure to radiation of CT scans as compared to plain radiographs. The aim of the present study was to compare the dose of exposure to radiation of a whole body CT scan to that of a plain radiograph protocol in an animal model for severely injured children. We chose 3 female pigs of different weights to serve as a model for children at different ages. 4 film radiation dosimeters (positioned on the eye, under the breast, paravertebrally on the thoracic spine and in the small pelvis, respectively) were implanted into every pig for each examination. Plain radiographs of the chest and the pelvis in one plane and of the skull and the complete spine in two planes were performed. The CT scan included skull, cervical spine and the whole body from the thorax to pelvis. The radiation dose of CT scans was 7 times higher as compared to the X-ray protocol, but the performance of CT scans was faster (8 vs. 18 min). The radiation dose of the whole body CT scan was at about 15 mSv. Based on our data and a review of the literature we will use whole body spiral CT scans as the preferred method in the primary radiological imaging of severely injured patients. In our opinion, the evident benefit of a reduced time of imaging in combination with superior image information outweighs the higher level of exposure to radiation.