The MACRA Act creates a Merit-Based Payment System, with monitoring patient exposure from CT providing one possible quality metric for meeting merit requirements. Quality metrics are also required by The Joint Commission, ACR, and CMS as facilities are tasked to perform reviews of CT irradiation events outside of expected ranges, review protocols for appropriateness, and validate parameters for low dose lung cancer screening. In order to efficiently collect and analyze irradiation events and associated DICOM tags, all clinical CT devices were DICOM connected to a parser which extracted dose related information for storage into a database. Dose data from every exam is compared to the appropriate external standard exam type. AAPM recommended CTDIvol values for head and torso, adult and pediatrics, coronary and perfusion exams are used for this study. CT doses outside the expected range were automatically formatted into a report for analysis and review documentation. CT Technologist textual content, the reason for proceeding with an irradiation above the recommended threshold, is captured for inclusion in the follow up reviews by physics staff. The use of a knowledge based approach in labeling individual protocol and device settings is a practical solution resulting in efficiency of analysis and review. Manual methods would require approximately 150 person-hours for our facility, exclusive of travel time and independent of device availability. An efficiency of 89% time savings occurs through use of this informatics tool including a low dose CT comparison review and low dose lung cancer screening requirements set forth by CMS.
DICOM Index Tracker (DIT) is an integrated platform to harvest rich information available from Digital Imaging and Communications in Medicine (DICOM) to improve quality assurance in radiology practices. It is designed to capture and maintain longitudinal patient-specific exam indices of interests for all diagnostic and procedural uses of imaging modalities. Thus, it effectively serves as a quality assurance and patient safety monitoring tool. The foundation of DIT is an intelligent database system which stores the information accepted and parsed via a DICOM receiver and parser. The database system enables the basic dosimetry analysis. The success of DIT implementation at Mayo Clinic Arizona calls for the DIT deployment at the enterprise level which requires significant improvements. First, for geographically distributed multi-site implementation, the first bottleneck is the communication (network) delay; the second is the scalability of the DICOM parser to handle the large volume of exams from different sites. To address this issue, DICOM receiver and parser are separated and decentralized by site. To facilitate the enterprise wide Quality Assurance (QA), a notable challenge is the great diversities of manufacturers, modalities and software versions, as the solution DIT Enterprise provides the standardization tool for device naming, protocol naming, physician naming across sites. Thirdly, advanced analytic engines are implemented online which support the proactive QA in DIT Enterprise.
KEYWORDS: Liver, Tissues, Signal attenuation, Dual energy imaging, Monte Carlo methods, Biopsy, X-ray computed tomography, Imaging spectroscopy, Visualization, Medicine
Nonalcoholic steatohepatitis (NASH) is a liver disease that occurs in patients that lack a history of the well-proven association of alcohol use. A major symptom of NASH is increased fat deposition in the liver. Gemstone Spectral Imaging (GSI) with fast kVp-switching enables projection-based material decomposition, offering the opportunity to accurately characterize tissue types, e.g., fat and healthy liver tissue, based on their energy-sensitive material attenuation and density. We describe our pilot efforts to apply GSI to locate and quantify the amount of fat deposition in the liver. Two approaches are presented, one that computes percentage fat from the difference in HU values at high and low energies and the second based on directly computing fat volume fraction at each voxel using multi-material decomposition. Simulation software was used to create a phantom with a set of concentric rings, each composed of fat and soft tissue in different relative amounts with attenuation values obtained from the National Institute of Standards and Technology. Monte Carlo 80 and 140 kVp X-ray projections were acquired and CT images of the phantom were reconstructed. Results demonstrated the sensitivity of dual energy CT to the presence of fat and its ability to distinguish fat from soft tissue. Additionally, actual patient (liver) datasets were acquired using GSI and monochromatic images at 70 and 140 keV were reconstructed. Preliminary results demonstrate a tissue sensitivity that appears sufficient to quantify fat content with a degree of accuracy as may be needed for non-invasive clinical assessment of NASH.
Coronary CT Angiography (CTA) is limited in patients with calcified plaque and stents. CTA is unable to
confidently differentiate fibrous from lipid plaque. Fast switched dual energy CTA offers certain advantages. Dual
energy CTA removes calcium thereby improving visualization of the lumen and potentially providing a more
accurate measure of stenosis. Dual energy CTA directly measures calcium burden (calcium hydroxyapatite) thereby
eliminating a separate non-contrast series for Agatston Scoring. Using material basis pairs, the differentiation of
fibrous and lipid plaques is also possible.
Patency of a previously stented coronary artery is difficult to visualize with CTA due to resolution
constraints and localized beam hardening artifacts. Monochromatic 70 keV or Iodine images coupled with Virtual
Non-stent images lessen beam hardening artifact and blooming. Virtual removal of stainless steel stents improves
assessment of in-stent re-stenosis.
A beating heart phantom with 'cholesterol' and 'fibrous' phantom coronary plaques were imaged with dual
energy CTA. Statistical classification methods (SVM, kNN, and LDA) distinguished 'cholesterol' from 'fibrous'
phantom plaque tissue. Applying this classification method to 16 human soft plaques, a lipid 'burden' may be useful
for characterizing risk of coronary disease. We also found that dual energy CTA is more sensitive to iodine contrast
than conventional CTA which could improve the differentiation of myocardial infarct and ischemia on delayed
acquisitions.
These phantom and patient acquisitions show advantages with using fast switched dual energy CTA for
coronary imaging and potentially extends the use of CT for addressing problem areas of non-invasive evaluation of
coronary artery disease.
KEYWORDS: Composites, Signal attenuation, X-ray computed tomography, Signal to noise ratio, Global system for mobile communications, Dual energy imaging, Iodine, Vector spaces, X-rays, Denoising
Dual energy x-ray CT images are computed using either image or projection data. The latter is thought to be preferable
for two-material decomposition. Nonetheless, using effective energies of polychromatic x-ray beams at separated kVp
values, material decomposition and pseudo-monochromatic reconstruction can be performed from reconstructed images.
This image-based approach generates added noise which should benefit from applying processing for noise reduction. A
set of material attenuation information so produced defines a vector space, which represents the true material property
but is predefined from mass attenuation coefficients of major body-composite materials. We assumed 53keV and 72keV
x-ray effective energies for 80kVp and 140kVp dual energy CT. The Gram-Schmidt process was applied to remove
noise orthogonal to the vector spaces of the body-composite materials. Two-material decomposition was performed, and
monochromatic and density images were reconstructed. Evaluations of image noise, Hounsfield unit accuracy, and
resolution with a phantom, as well as with abdominal images, demonstrates improved CNR and SNR without loss of
detail. This method of noise suppression also produced high quality density maps of two basis materials. Since dual
energy CT currently uses slightly above average radiation dose, this method has the potential for lowering dose in
addition to improving image quality.
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