William Pavlicek

Iterative Reconstruction Technique for Reducing Body Radiation Dose at CT: Feasibility Study

OBJECTIVE The purpose of this study was to evaluate the image noise, low-contrast resolution, image quality, and spatial resolution of adaptive statistical iterative reconstruction in low-dose body CT. MATERIALS AND METHODS Adaptive statistical iterative reconstruction was used to scan the American College of Radiology phantom at the American College of Radiology reference value and at one-half that value (12.5 mGy). Test objects in low- and high-contrast and uniformity modules were evaluated. Low-dose CT with adaptive statistical iterative reconstruction was then tested on 12 patients (seven men, five women; average age, 67.5 years) who had previously undergone routine-dose CT. Two radiologists blinded to scanning technique evaluated images of the same patients obtained with routine-dose CT and low-dose CT with and without adaptive statistical iterative reconstruction. Image noise, low-contrast resolution, image quality, and spatial resolution were graded on a scale of 1 (best) to 4 (worst). Quantitative noise measurements were made on clinical images. RESULTS In the phantom, low- and high-contrast and uniformity assessments showed no significant difference between routine-dose imaging and low-dose CT with adaptive statistical iterative reconstruction. In patients, low-dose CT with adaptive statistical iterative reconstruction was associated with CT dose index reductions of 32-65% compared with routine imaging and had the least noise both quantitatively and qualitatively (p < 0.05). Low-dose CT with adaptive statistical iterative reconstruction and routine-dose CT had identical results for low-contrast resolution and nearly identical results for overall image quality (grade 2.1-2.2). Spatial resolution was better with routine-dose CT (p = 0.004). CONCLUSION These preliminary results support body CT dose index reductions of 32-65% when adaptive statistical iterative reconstruction is used. Studies with larger statistical samples are needed to confirm these findings.

Innovations in CT Dose Reduction Strategy: Application of the Adaptive Statistical Iterative Reconstruction Algorithm

OBJECTIVE The purpose of this article is to discuss the application of a new CT reconstruction algorithm, adaptive statistical iterative reconstruction (ASIR), to reduce radiation dose at body CT and to provide imaging examples in comparison with low-dose and standard-dose filtered back projection CT. CONCLUSION The ASIR reconstruction algorithm is a promising technique for providing diagnostic quality CT images at significantly reduced radiation doses.

Abdominal CT: Comparison of Low-Dose CT With Adaptive Statistical Iterative Reconstruction and Routine-Dose CT With Filtered Back Projection in 53 Patients

OBJECTIVE The purpose of this article is to retrospectively compare radiation dose, noise, and image quality of abdominal low-dose CT reconstructed with adaptive statistical iterative reconstruction (ASIR) and routine-dose CT reconstructed with filtered back projection (FBP). MATERIALS AND METHODS Fifty-three patients (37 men and 16 women; mean age, 60.8 years) underwent contrast-enhanced abdominal low-dose CT with 40% ASIR. All 53 patients had previously undergone contrast-enhanced routine-dose CT with FBP. With the scanning techniques masked, two radiologists independently graded images for sharpness, image noise, diagnostic acceptability, and artifacts. Quantitative measures of radiation dose and image noise were also obtained. All results were compared on the basis of body mass index (BMI). RESULTS The volume CT dose index (CTDI(vol)), dose-length product, and radiation dose for low-dose CT with ASIR were 17 mGy, 860 mGy, and 13 mSv, respectively, compared with 25 mGy, 1,193 mGy, and 18 mSv for routine-dose CT with FBP, representing an approximate overall dose reduction of 33%. Low-dose CT with ASIR had significantly reduced (p < 0.001) quantitative and qualitative assessment of image noise. Image sharpness, however, was significantly reduced for low-dose CT with ASIR (p < 0.001), although diagnostic acceptability and artifact scores were nearly identical to those for routine-dose CT with FBP. The average CTDI(vol) dose reduction was 66% for patients with a BMI of less than 20 and 23% for patients with a BMI of 25 or greater. CONCLUSION Compared with routine-dose CT with FBP, abdominal low-dose CT with ASIR significantly reduces noise, thereby permitting diagnostic abdominal examinations with lower (by 23-66%) radiation doses. Despite reduced image sharpness in average and small patients, low-dose CT with ASIR had diagnostic acceptability comparable to that of routine-dose CT with FBP.

Dual-Energy (Spectral) CT: Applications in Abdominal Imaging

Dual-energy imaging is a promising new development in computed tomography (CT) that has the potential to improve lesion detection and characterization beyond levels currently achievable with conventional CT techniques. In dual-energy CT (DECT), the simultaneous use of two different energy settings allows the differentiation of materials on the basis of their energy-related attenuation characteristics (material density). The datasets obtained with DECT can be used to reconstruct virtual unenhanced images as well as iodinated contrast material-enhanced material density images, obviating the standard two-phase (unenhanced and contrast-enhanced) scanning protocol and thus helping minimize the radiation dose received by the patient. Single-source DECT, which is performed with rapid alternation between two energy levels, can also generate computed monochromatic images, which are less vulnerable to artifacts such as beam hardening and pseudoenhancement and provide a higher contrast-to-noise ratio than polychromatic images produced by conventional CT. Familiarity with the capabilities of DECT may help radiologists improve their diagnostic performance.

How I Do It: Managing Radiation Dose in CT

Computed tomography (CT) is an imaging test that is widely used worldwide to establish medical diagnoses and perform image-guided interventions. More recently, concern has been raised about the risk of carcinogenesis from medical radiation, with a focus on CT. The purpose of this article is to (a) describe the importance of educating radiology personnel, patients, and referring clinicians about the concerns over CT radiation, (b) describe commonly used CT parameters and radiation units, (c) discuss the importance of establishing a dedicated radiology team to manage CT radiation, and (d) describe specific CT techniques to minimize radiation while providing diagnostic examinations.

An automated DICOM database capable of arbitrary data mining (Including Radiation Dose Indicators) for quality monitoring

The U.S. National Press has brought to full public discussion concerns regarding the use of medical radiation, specifically x-ray computed tomography (CT), in diagnosis. A need exists for developing methods whereby assurance is given that all diagnostic medical radiation use is properly prescribed, and all patients’ radiation exposure is monitored. The “DICOM Index Tracker©” (DIT) transparently captures desired digital imaging and communications in medicine (DICOM) tags from CT, nuclear imaging equipment, and other DICOM devices across an enterprise. Its initial use is recording, monitoring, and providing automatic alerts to medical professionals of excursions beyond internally determined trigger action levels of radiation. A flexible knowledge base, aware of equipment in use, enables automatic alerts to system administrators of newly identified equipment models or software versions so that DIT can be adapted to the new equipment or software. A dosimetry module accepts mammography breast organ dose, skin air kerma values from XA modalities, exposure indices from computed radiography, etc. upon receipt. The American Association of Physicists in Medicine recommended a methodology for effective dose calculations which are performed with CT units having DICOM structured dose reports. Web interface reporting is provided for accessing the database in real-time. DIT is DICOM-compliant and, thus, is standardized for international comparisons. Automatic alerts currently in use include: email, cell phone text message, and internal pager text messaging. This system extends the utility of DICOM for standardizing the capturing and computing of radiation dose as well as other quality measures.

Active matrix liquid crystal displays for clinical imaging: comparison with cathode ray tube displays.

Fifteen large-area, flat-panel displays used for clinical image review were evaluated for image quality and compared with 30 comparably sized cathode ray tube (CRT) monitors. Measurements were of image display patterns by Video Electronic Standards Association (VESA) and a commercial product. Field measurements were made of maximum and minimum luminance, ambient lighting, characteristic curve (gamma), point shape and size, high-contrast resolution, uniformity, and distortion. Assessments were made of pixel defects, latent image patterns, ghosting artifacts, and viewing angle luminance. Also, a questionnaire was generated for users of the flat-panel and CRT units. Seventeen respondents indicated no preference for either flat panel or CRT. Results show these flat panels to have higher luminance (mean, 177.7 cd/m2); larger number of just noticeable differences (JNDs; n=555), higher gamma, comparable uniformity, and warm-up time. CRTs had less angle viewing dependence and far fewer artifacts (ghosting and latent images). Our questionnaire showed active matrix liquid crystal displays (AMLCD) to be fully acceptable for clinical image viewing. Furthermore, the statistical results show that further testing for new AMLCDs of this type is unwarranted.

Reducing Body CT Radiation Dose: Beyond Just Changing the Numbers

OBJECTIVE CT dose reduction has become a top priority for many radiology practices as a result of federal and state initiatives and public concern. Implementing this in practice, however, is difficult because of the variability between practices, CT scanners, radiologist preferences, and institutional capacity. CONCLUSION This article will discuss strategies for successful CT dose reduction instituted in multivendor practices.

Dynamics of Diastolic Sounds Caused by Partially Occluded Coronary Arteries

The aim of this project is to improve the detection of coronary occlusions using an approach based on the recording and analysis of isolated diastolic heart sounds associated with turbulent blood flow in occluded coronary arteries. The nonlinear dynamic analysis method based on approximate entropy has been proposed for the analysis of diastolic heart sounds. A commercially available electronic stethoscope was used to record the diastolic heart sounds from patients diagnosed with or without coronary artery disease (CAD) based on their coronary angiography examination. The nonlinear dynamical analysis (approximate entropy) measures of the diastolic heart sounds recorded from 30 patients with coronary occlusions and ten normal subjects were estimated. Results suggest the presence of the high nonlinear (approximate entropy) values of diastolic heart sounds associated with CAD ( p < 0.05). This approach led to a sensitivity of 77%, a specificity of 80%, and an overall accuracy of 78%. As a summary, 23 out of 30 abnormal patients and eight out of ten normal patients were correctly detected.

Spectral Analysis of Heart Sounds Associated With Coronary Occlusions

Numerous studies based on the spectral analysis of diastolic sounds showed an increase in the high frequency portion of the spectrum for patients with coronary artery disease (CAD) compared with normal patients. The overall goal of this study is to detect the presence of coronary artery disease in patients using a noninvasive and inexpensive approach. A commercially available electronic stethoscope was used to record the diastolic heart sounds from patients diagnosed with or without CAD based on their coronary angiography examination. The Fast Fourier Transform, a widely used signal processing method, was then implemented on the diastolic segments. The power ratios of the energy above 130 Hz to the energy below 130 Hz were calculated for normal and abnormal patients and compared. Results furthermore confirmed that patients with CAD have more energy in the higher portion of their spectrum, resulting in higher power ratios than for normal patients (p < 0.05). This approach led to a sensitivity of 71%, a specificity of 83% and an overall accuracy of 73.3% using an optimal threshold ratio of 1.5. These results suggest that the proposed system could be used in clinics as part of standard physical examinations.