Helical cone beam CT with an asymmetrical detector.

If a multislice or other area detector is shifted to one side to cover a larger field of view, then the data are truncated on one side. We propose a method to restore the missing data in helical cone-beam acquisitions that uses measured data on the longer side of the asymmetric detector array. The method is based on the idea of complementary rays, which is well known in fan beam geometry; in this paper we extend this concept to the cone-beam case. Different cases of complementary data coverage and dependence on the helical pitch are considered. The proposed method is used in our prototype 16-row CT scanner with an asymmetric detector and a 700 mm field of view. For evaluation we used scanned body phantom data and computer-simulated data. To simulate asymmetric truncation, the full, symmetric datasets were truncated by dropping either 22.5% or 45% from one side of the detector. Reconstructed images from the prototype scanner with the asymmetrical detector show excellent image quality in the extended field of view. The proposed method allows flexible helical pitch selection and can be used with overscan, short-scan, and super-short-scan reconstructions.

The potential for community-based health information exchange systems to reduce hospital readmissions.

BACKGROUND: Hospital readmissions are common, costly, and offer opportunities for utilization reduction. Electronic health information exchange (HIE) systems may help prevent readmissions by improving access to clinical data by ambulatory providers after discharge from the hospital. OBJECTIVE: We sought to determine the association between HIE system usage and 30-day same-cause hospital readmissions among patients who consented and participated in an operational community-wide HIE during a 6-month period in 2009-2010. METHODS: We identified a retrospective cohort of hospital readmissions among adult patients in the Rochester, New York area. We analyzed claims files from two health plans that insure more than 60% of the area population. To be included in the dataset, patients needed to be continuously enrolled in the health plan with at least one encounter with a participating provider in the 6 months following consent to be included in the HIE system. Each patient appeared in the dataset only once and each discharge could be followed for at least 30 days. RESULTS: We found that accessing patient information in the HIE system in the 30 days after discharge was associated with a 57% lower adjusted odds of readmission (OR 0.43; 95% CI 0.27 to 0.70). The estimated annual savings in the sample from averted readmissions associated with HIE usage was $605 000. CONCLUSIONS: These findings indicate that usage of an electronic HIE system in the ambulatory setting within 30 days after hospital discharge may effectively prevent hospital readmissions, thereby supporting the need for ongoing HIE efforts.

Patient-centered medical homes: observable types derived from national recognition assessment scores.

The patient-centered medical home (PCMH) is a strategy to transform primary care delivery organizations. However, PCMHs take on many forms and can "look different." To better understand the activities of organizations undertaking this strategy, we sought to identify discernible PCMH types using cluster analyses. From a sample of level 3 National Committee for Quality Assurance PCMHs, We extracted 3 types of PCMHs: information-focused, efficiency-focused, and high-scoring. Our findings confirm that the PCMH is not a uniform intervention. Characterizing PCMHs with particular areas of focus has implications for understanding the transformation process, identifying areas for continued practice development, and advancing evaluation of this organizational model.

Feldkamp-based cone-beam reconstruction for gantry-tilted helical multislice CT.

Depending on the clinical application, it is frequently necessary to tilt the gantry of an x-ray CT system with respect to the patient and couch. For single-slice fan-beam systems, tilting the gantry introduces no errors or artifacts. Most current systems, however, are helical multislice systems with up to 16 slices. The multislice helical reconstruction algorithms used to create CT images must be modified to account for tilting of the gantry. If they are not, the quality of reconstructed images will be poor with the presence of significant artifacts, such as smearing and double-imaging of anatomical structures. Current CT systems employ three primary types of reconstruction algorithms: helical fan-beam approximation, advanced single-slice rebinning, and Feldkamp-based algorithms. This paper presents a generalized helical cone-beam Feldkamp-based algorithm that is valid for both tilted and nontilted orientations of the gantry. Unlike some of the other algorithms, generalization of the Feldkamp algorithm to include gantry tilt is simple and straightforward with no significant increase in computational complexity. The effect of gantry tilt for helical Feldkamp reconstruction is to introduce a lateral shift in the isocenter of the reconstructed slice of interest, which is a function of the tilt, couch speed, and view angle. The lateral shift is easily calculated and incorporated into the helical Feldkamp backprojection algorithm. A tilt-generalized helical Feldkamp algorithm has been developed and incorporated into Aquilion 16-slice CT (Toshiba, Japan) scanners. This paper describes modifications necessary for the tilt generalization and its verification.

The cause of the artifact in 4-slice helical computed tomography.

The causes of the image artifacts in a 4-slice helical computed tomography have been discussed as follows: (1) changeover in pairs of data used in z interpolation, (2) sampling interval in z, and (3) the cone angle. This study analyzes the first two causes of the artifact and describes how the current algorithm [K. Taguchi and H. Aradate, Radiology 205P, 390 (1997); 205P, 618 (1997); Med. Phys. 25, 550-561 (1998); H. Hu, ibid. 26, 5-18 (1999); S. Schaller et al., IEEE Trans. Med. Imaging 19, 822-834 (2000); K. Taguchi, Ph.D. thesis, University of Tsukuba, 2002] solves the problem. An interpolated sinogram for a slice at the edge of a ball phantom shows discontinuity caused by the changeover. If we extend the streak artifact in the reconstructed image, it crosses the focus orbit at the corresponding projection angle. Applying z filtering can reduce such causes by its feathering effect and mixing data obtained by different cone angles; the best results are provided when z filtering is applied to densely sampled helical data.

A new weighting scheme for cone-beam helical CT to reduce the image noise.

Reducing the patient dose while keeping the image noise at the same level is desired for x-ray CT examinations. In order to achieve the goal, we propose a new weighting scheme taking the validity of the data and redundant data samples into account. The method is evaluated with a new generalized version of the Feldkamp helical reconstruction algorithm. It allows us to enlarge the projection angular range used in reconstruction, and thus, to reduce the image noise by increasing the detector utilization rate to 100% without sacrificing the image quality or z-resolution. This concept can be adapted to other exact or approximate algorithms as far as they use redundant data samples.

Health information exchange and the frequency of repeat medical imaging.

OBJECTIVES: Medical imaging, which is expensive, is frequently repeated for the same patient within a relatively short period of time due to lack of access to previous images. Health information exchange (HIE) may reduce repeat imaging by facilitating provider access to prior images and reports. We sought to determine the effect of an HIE system on the occurrence of repeat imaging. STUDY DESIGN AND METHODS: We conducted a cohort study of adult patients who consented to participate in a community-based HIE system in an 11-county region in New York. Using data from 2009-2010, we linked log files of provider HIE usage to administrative claims data from 2 commercial health plans. Using generalized estimation equations, we measured the association between HIE system access and repeat imaging within 90 days. RESULTS: Of 196,314 patients in the cohort, 34,604 (18%) of patients had at least 1 imaging procedure, which was equivalent to a rate of 28.7 imaging procedures per 100 patients. Overall, 7.7% of images were repeated within 90 days. If the HIE system was accessed within the 90 days following an initial imaging procedure, imaging was significantly less likely to be repeated (5% repeated with HIE access vs 8% repeated without HIE access, P < .001). HIE system access reduced the adjusted odds of a repeat image by 25% (95% CI, 13%-35%). CONCLUSIONS: Use of the HIE system to access previous patient information was associated with a reduction in repeated imaging.

Optimized reconstruction algorithm for helical CT with fractional pitch between 1PI and 3PI.

We propose an approximate approach to use redundant data outside the 1PI window within the exact Katsevich reconstruction framework. The proposed algorithm allows a flexible selection of the helical pitch, which is useful for clinical applications. Our idea is an extension of the one proposed by KOhler, Bontus, and Koken (2006). It is based on optimizing the contribution weights of convolution families used in exact Katsevich 3PI algorithms, so that the total weight of each Radon plane is as close to 1 as possible. Optimization is based on solving a least squares problem subject to linear constrains. Numerical evaluation shows good noise and artifact reduction properties of the proposed algorithm.