Oleg S. Pianykh

Digital Imaging and Communications in Medicine (DICOM)

Foreword This Supplement to the DICOM Standard introduces the SR SOP Classes for transmission and storage of documents that describe or refer to any number of images or waveforms or to the specific features that they contain. The SR SOP Classes fully support conventional free text reports and provide the capability 4 to record structured information that enhances the precision, clarity and value of clinical documents. The SR SOP Classes allow users to link text and other data to particular images and/or waveforms and to store the coordinates of findings so that users can see exactly what is being described in a report. In addition, users can label, index and retrieve clinically-relevant information using codes. SR SOP Classes 8 can be used in a variety of clinical contexts. For example:-in CT or MRI to convey the interpretation text, to record the DICOM identifiers of selected images and to denote the spatial coordinates of significant findings;-in ultrasound to transmit measurements; and 12-in cardiac catheterization laboratories to record a procedure log that time-stamps and describes significant measurements and interventions and link together all of the related images, waveforms, interpretation reports and related information into a convenient unit-record.

Dose Reduction in Computed Tomographic Angiography of Pregnant Patients With Suspected Acute Pulmonary Embolism

Purpose: The aim of this study was to quantify the effect of a reduced-dose pulmonary computed tomographic (CT) angiography protocol on radiation dose and image quality in pregnant patients as compared with a standard protocol. Materials and Methods: Twenty-six pregnant women with suspected pulmonary embolism underwent reduced-dose CT angiography (200 mA and 100 kV, from the aortic arch to the diaphragm). The matched control group standard protocol was 400 mA, 120 kilovolt (peak), and the entire thorax. The CT dose index, dose-length product, effective dose, image quality, and signal-to-noise ratio were assessed and compared with the Wilcoxon rank sum test result. Results: The CT dose index, mean dose-length product, and calculated effective dose were lower in the pregnancy group than in the controls: mean (SD), 5.21 (1.54) mGy versus 20.86 (5.59) mGy; 105.65 (39.77) mGy cm versus 575.71 (154.86) mGy cm, and 1.79 (0.676) msv versus 9.787 (2.63) msv, respectively (P < 0.0001). Quality scores of segmental (P = 0.266) and subsegmental (P = 0.207) arteries and arterial attenuation (P = 0.443) were similar. Conclusions: In pregnant patients with suspected pulmonary embolism, combined reduction of kilovoltage and milliampere-second settings and z-axis coverage results in a substantial reduction of radiation dose while maintaining diagnostic imaging quality.

A fast and accurate method to register medical images using Wavelet Modulus Maxima

Abstract This paper presents a fast, accurate and automatic method to register images of rigid bodies. It uses wavelets to obtain control points. Wavelets are not shift invariant but the structures determined by the wavelet high pass image, the Modulus Maxima Image, provide the information necessary for a fast-rough convergence. These structures represent shapes from which we segment the invariant shapes for the images being registered. For example, the MRI and CT images of the brain can be considered as rigid bodies that do not undergo a change in shape over reasonable periods of time. By using a convex hull, we make the procedure insensitive to the internal changes in the object. Hence, even with the growth of tumors, the procedure registers brain images very accurately. The method uses the correlation coefficient to measure the similarity between images and to determine how well the images are registered. The method has been extensively tested with various types of images and in all cases the registration accuracy is very high. The correlation coefficient used to validate the registrations has deficiencies that occasionally required a visual inspection to terminate the algorithm after a point of marginal improvement.

Analytically tractable case of fuzzy c-means clustering

In this paper, we offer a simple and accurate clustering algorithm which was derived as a closed-form analytical solution to a cluster fit function minimization problem. As a result, the algorithm finds the global minimum of the fit function, and combines exceptional efficiency with optimal clustering results.

Coronary CTA using scout-based automated tube potential and current selection algorithm, with breast displacement results in lower radiation exposure in females compared to males

PURPOSE To evaluate the effect of automatic tube potential selection and automatic exposure control combined with female breast displacement during coronary computed tomography angiography (CCTA) on radiation exposure in women versus men of the same body size. MATERIALS AND METHODS Consecutive clinical exams between January 2012 and July 2013 at an academic medical center were retrospectively analyzed. All examinations were performed using ECG-gating, automated tube potential, and tube current selection algorithm (APS-AEC) with breast displacement in females. Cohorts were stratified by sex and standard World Health Organization body mass index (BMI) ranges. CT dose index volume (CTDIvol), dose length product (DLP) median effective dose (ED), and size specific dose estimate (SSDE) were recorded. Univariable and multivariable regression analyses were performed to evaluate the effect of gender on radiation exposure per BMI. RESULTS A total of 726 exams were included, 343 (47%) were females; mean BMI was similar by gender (28.6±6.9 kg/m(2) females vs. 29.2±6.3 kg/m(2) males; P=0.168). Median ED was 2.3 mSv (1.4-5.2) for females and 3.6 (2.5-5.9) for males (P<0.001). Females were exposed to less radiation by a difference in median ED of -1.3 mSv, CTDIvol -4.1 mGy, and SSDE -6.8 mGy (all P<0.001). After adjusting for BMI, patient characteristics, and gating mode, females exposure was lower by a median ED of -0.7 mSv, CTDIvol -2.3 mGy, and SSDE -3.15 mGy, respectively (all P<0.01). CONCLUSIONS We observed a difference in radiation exposure to patients undergoing CCTA with the combined use of AEC-APS and breast displacement in female patients as compared to their BMI-matched male counterparts, with female patients receiving one third less exposure.

Radiation Dose Consideration in Kidney Stone CT Examinations: Integration of Iterative Reconstruction Algorithms With Routine Clinical Practice

OBJECTIVE The objective of our study was to evaluate three commercially available iterative reconstruction (IR) algorithms-ASiR, iDOSE, and SAFIRE-and conventional filtered back projection (FBP) on image quality and radiation dose in kidney stone CT examinations. MATERIALS AND METHODS During the 6-month study period, 684 unenhanced kidney stone CT examinations of consecutive adults were performed on 17 CT scanners (GE Healthcare [vendor 1], n = 12 scanners; Philips Healthcare [vendor 2], n = 2; Siemens Health-care [vendor 3], n = 3); these examinations were retrieved using dose-monitoring software (eXposure). A total of 347 kidney stone CT examinations were reconstructed using FBP, and 337 examinations were processed using IR (ASiR, n = 248; iDOSE, n = 50; SAFIRE, n = 39). The standard-dose scanning parameters for FBP scanners included a tube potential of 120 kVp, a tube current of 75-450 mA for vendor 1 and a Quality Reference mAs of 160-180 for vendor 3, and a slice thickness of 2.5 or 5 mm. The dose-modified protocol for the IR scanners included a higher noise index (1.4 times higher than the standard-dose FBP protocol) for vendor 1, a lower reference tube current-exposure time product for vendor 2 (150 reference mAs), and a lower Quality Reference mAs for vendor 3 (120 Quality Reference mAs). Three radiologists independently reviewed 60 randomly sampled kidney stone CT examinations for image quality, noise, and artifacts. Objective noise and attenuation were also determined. Size-specific dose estimates (SSDEs) were compared using ANOVA. RESULTS Significantly higher subjective and objective measurements of image noise were found in FBP examinations compared with dose-modified IR examinations (p < 0.05). The radiation dose was substantially lower for the dose-modified IR examinations than the standard-dose FBP examinations (mean SSDE ± SD: 8.1 ± 3.8 vs 11.6 ± 3.6 mGy, respectively) (p < 0.0001), but the radiation dose was comparable among the three IR techniques (ASiR, 7.8 ± 3.1 mGy; iDOSE, 7.5 ± 1.9 mGy; SAFIRE, 7.6 ± 3.2 mGy) (p > 0.05). CONCLUSION The three IRs enable 20-33% radiation dose reduction in kidney stone CT examinations compared with the FBP technique without any image quality concerns. The radiation dose and image quality were comparable among these three IR algorithms.

Body Tumor CT Perfusion Protocols: Optimization of Acquisition Scan Parameters in a Rat Tumor Model

PURPOSE To evaluate the effects of total scanning time (TST), interscan delay (ISD), inclusion of image at peak vascular enhancement (IPVE), and selection of the input function vessel on the accuracy of tumor blood flow (BF) calculation with computed tomography (CT) in an animal model. MATERIALS AND METHODS All animal protocols and experiments were approved by the institutional animal care and use committee prior to study initiation. After injection of 0.2 or 0.4 mL of iodinated contrast material, six rats with mammary adenocarcinoma (three tumors each) were scanned in the axial mode for 5 minutes with 1-second ISD (reference scan), 2.5-mm section thickness, 2.5-mm interval, pitch of 1.3, 120 kV, 240 mA, and 0.5-second rotation time. A total of 126 dynamic data sets were created with commercial software by varying TST and ISD, including or excluding the IPVE, and using the aorta or inferior vena cava (IVC) as the input function. Comparative analyses were used to test for significant differences (t test, Wilcoxon signed rank test). Regression analysis was performed to assess the relationship between attenuation of the input function vessel and BF. RESULTS No significant difference was observed (P > .05) when TST was as short as 30 seconds (range, 20-23 mL/100 g). In sequences performed with an ISD longer than 8 seconds, BF was significantly elevated (P < .01). Inclusion of the IPVE eliminated this difference (P > .10). Use of the IVC as the input function resulted in significantly higher BF (P < .02), with a correlation between peak attenuation and BF (R(2) = 0.43). CONCLUSION To reduce radiation dose in tumor perfusion with CT, TST can be reduced without causing significant changes in BF calculation in an animal model. Scanning the aortic reference with peak contrast enhancement reduces variability sufficiently to allow for longer ISDs.

Nearly-lossless autoregressive image compression

Abstract A flexible accurate technique for improving image compression properties with linear image compressing transforms is presented. This is a reliable iterative algorithm for the nearly-lossless autoregressive (NLAR) compression of images, which permits control of errors produced in each pixel intensity while preserving the original image intensity range. The convergence of this new algorithm is demonstrated, both theoretically and numerically. Its relationship to other types of nearly-lossless compression, as well as to traditional lossless and lossy approaches, is discussed.

Improved Monte Carlo form factor integration

Abstract Form factors are used in radiosity image synthesis to describe the fraction of diffusely reflected light leaving one surface and reaching another. They incorporate fundamental geometric properties of interacting surfaces used for light transfer computation.Many numerical applications such as realistic image synthesis require accurate and simple formula for the form factors from small oriented differential areas (treated as a point with a normal) to different geometrical objects; a disk was used in this paper. The exact analytic solution for the general point-to-disk form factor integral is used to develop more accurate numerical techniques for form factor integration for surfaces commonly in use. The improvements are illustrated with realistic image synthesis.

Integer wavelet transformations with predictive coding improves 3D similar image set compression

Lossless compression techniques are essential in archival and communication of large amounts of homogeneous data in radiological image databases. This paper exploits dependencies that exist between the pixel intensities in three dimensions to improve compression for a set of similar medical images. These 3-D dependencies are systematically presented as histograms, plots of wavelet decomposition coefficients, feature vectors of wavelet decomposition coefficients, entropy and correlation. This 3-D dependency is called set redundancy for medical image sets. Predictive coding is adapted to set redundancy and combined with integer wavelet transformations to improve compression. This set compression improvement is demonstrated with 3-D sets of magnetic resonance (MR) brain images.