Hajime Harauchi

Time and flow study results before and after installation of a hospital information system and radiology information system and before clinical use of a picture archiving and communication system.

The effectiveness of a hospital information system (HIS) and a radiological information system (RIS) was evaluated to optimize preparation for the planned full clinical operation of a picture archiving and communication system (PACS), which is now linked experimentally to the HIS and the RIS. One thousand IC (integrated circuit) cards were used for time studies and flow studies in the hospital. Measurements were performed on image examination order entry, image examination, reporting, and image delivery times. Even though after the HIS and the RIS operation only a small amount of time savings were realized in each time fraction component, such as in the patient movement time, examination time, and film delivery time, the total turn-around time was shortened markedly, by more than 23 hours on average. It was verified that the HIS and the RIS was beneficial in the outpatient clinics of the orthopedic department. Our method of measurement employing IC cards before and after HIS and RIS operations can be applied in other hospitals.

Determination of 3D positions of pacemaker leads from biplane angiographic sequences.

In vitro and in vivo analyses of stress on pacemaker leads and their components during the heart cycle have become especially important because of incidences of failure of some of these mechanical components. For stress analyses, the three-dimensional (3D) position, shape, and motion of the pacemaker leads must be known accurately at each time point during the cardiac cycle. We have developed a method for determination of the in vivo 3D positions of pacemaker leads during the entire heart cycle. Sequences of biplane images of patients with pacemakers were obtained at 30 frames/s for each projection. The sequences usually included at least two heart cycles. After patient imaging, biplane images of a calibration object were obtained from which the biplane imaging geometry was determined. The centerlines of the leads and unique, identifiable points on the attached electrodes were indicated manually for all acquired images. Temporal interpolation of the lead and electrode data was performed so that the temporal nonsynchronicity of the image acquisition was overcome. Epipolar lines, generated from the calculated geometry, were employed to identify corresponding points along the leads in the pairs of biplane images for each time point. The 3D positions of the lead and electrodes were calculated from the known geometry and from the identified corresponding points in the images. Using multiple image sets obtained with the calibration object at various orientations, the precision of the calculated rotation matrix and of the translation vector defining the imaging geometry was found to be approximately 0.7 degree and 1%, respectively. The 3D positions were reproducible to within 2 mm, with the error lying primarily along the axis between the focal spot and the imaging plane. Using data obtained by temporally downsampling to 15 frames/s, the interpolated data were found to lie within approximately 2 mm of the true position for most of the heart cycle. These results indicate that, with this technique, one can reliably determine pacemaker lead positions throughout the heart cycle, and thereby it will provide the basis for stress analysis on pacemaker leads.

Evaluation of imaging geometries calculated from biplane images

A technique is developed that will calculate accurate and reliable imaging geometries and three-dimensional (3D) positions from biplane images of a calibration phantom. The calculated data provided by our technique will facilitate accurate 3D analysis in various clinical applications. Biplane images of a Lucite cube containing lead beads 1 mm in diameter were acquired. After identifying corresponding beads in both images and calculating their image positions, the 3D positions of the beads relative to each focal spot were determined. From these data, the transformation relating the 3D configurations were calculated to give the imaging geometry relating the biplane views. The 3D positions of objects were determined from the biplane images along with the corresponding imaging geometries. In addition, methods are developed to evaluate the quality of the calculated results on a case-by-case basis in the clinical setting. Methods are presented for evaluating the reproducibility of the calculated geometries and 3D positions, the accuracy of calculated object sizes, and the effects of errors due to time jitter, variation in user-indication, centering, and distortions on the calculated geometries and 3D reconstructions. The precision of the translation vectors and rotation matrices of the calculated geometries were within 1% and 1 degree, respectively, in phantom studies, with estimated accuracies of approximately 0.5% and 0.4 degree, respectively, in simulation studies. The precisions of the absolute 3D positions and orientations of the calculated 3D reconstructions were approximately 2 mm and 0.5 degree, respectively, in phantom studies, with estimated accuracies of approximately 1.5 mm and 0.4 degree, respectively, in simulation studies. This technique will provide accurate and precise imaging geometries as well as 3D positions from biplane images, thereby facilitating 3D analysis in various clinical applications. We believe that the study presented here is unique in that it represents the first steps toward understanding and evaluating the reliability of these 3D calculations in the clinical situation.

An algorithm for mapping the catheter tip position on a fluorograph to the three-dimensional position in magnetic resonance angiography volume data

This paper proposes an algorithm which maps the position of a catheter tip on a fluorograph to the 3D position in magnetic resonance angiography (MRA) data. This algorithm was assessed for its accuracy. We designed an algorithm consisting of a registration step and a recognition step. The registration step registers MRA and fluorography data using a digital subtraction angiography (DSA) image. The recognition step recognizes the position in the MRA data corresponding to the catheter tip position on a fluorograph. We checked the accuracy of the recognition step by employing an artificial data set consisting of 3D image data (64 x 64 x 64 matrix) and its projection image (92 x 92 matrix) and the accuracy of the registration step with the aid of three of the 3D time-of-flight MRA data sets (256 x 256 matrix and 60 slices) and their projection images in the form of DSA images. The accuracy of the recognition step depended upon that of the registration. When there was no misregistration, all of the mean errors were less than 0.2 mm. The mean errors of the registration step were 0.273 mm and 0.226 mm, respectively, for the longitudinal shift along the X and Y axes, 0.478 degrees, 1.203 degrees and 0.208 degrees, respectively, for the rotation angles around the X, Y and Z axes and 0.020 times for the magnification. The mean image error between the projection image of the registered MRA data and that of the MRA data which were employed as the DSA image was 0.034 mm.

Analysis of 3D motion of in-vivo pacemaker leads

In vivo analyses of pacemaker lead motion during the cardiac cycle have become important due to incidences of failure of some of the components. For the calculation and evaluation of in vivo stresses in pacemaker leads, the 3D motion of the lead must be determined. To accomplish this, we have developed a technique for calculation of the overall and relative 3D position, and thereby the 3D motion, of in vivo pacemaker leads through the cardiac cycle.Biplane image sequences of patients with pacemakers were acquired for at least two cardiac cycles. After the patient acquisitions, biplane images of a calibration phantom were obtained. The biplane imaging geometries were calculated from the images of the calibration phantom. Points on the electrodes and the lead centerlines were indicated manually in all acquired images. The indicated points along the leads were then fit using a cubic spline. In each projection, the cumulative arclength along the centerlines in two temporally adjacent images was used to identify corresponding points along the centerlines. To overcome the non-synchronicity of the biplane image acquisition, temporal interpolation was performed using these corresponding points based on a linear scheme. For each time point, corresponding points along the lead centerlines in the pairs of biplane images were identified using epipolar lines. The 3D lead centerlines were calculated from the calculated imaging geometries and the corresponding image points along the lead centerlines. From these data, 3D lead motion and the variations of the lead position with time were calculated and evaluated throughout the cardiac cycle. The reproducibility of the indicated lead centerlines was approximately 0.3 mm. The precision of the calculated rotation matrix and translation vector defining image geometry were approximately 2 mm. 3D positions were reproducible to within 2 mm. Relative positional errors were less than 0.3 mm. Lead motion correlated strongly with phases of the cardiac cycle. Our results indicate that complex motions of in vivo pacemaker leads can be precisely determined. Thus, we believe that this technique will provide precise 3D motion and shapes on which to base subsequent stress analysis of pacemaker lead components.

An Inductive Method for Automatic Generation of Referring Physician Prefetch Rules for PACS

To prefetch images in a hospital-wide picture archiving and communication system (PACS), a rule must be devised to permit accurate selection of examinations in which a patients images are stored. We developed an inductive method to compose prefetch rules from practical data which were obtained in a hospital using a decision tree algorithm. Our methods were evaluated on data acquired in Osaka University Hospital for one month. The data collected consisted of 58,617 cases of consultation reservations, 643,797 examination histories of patients, and 323,993 records of image requests in PACS. Four parameters indicating whether the images of the patient were requested or not for each consultation reservation were derived from the database. As a result, the successful selection sensitivity for consultations in which images were requested was approximately 0.8, and the specificity for excluding consultations accurately where images were not requested was approximately 0.7.

Automatic segmentation method which divides a cerebral artery tree in time-of-flight MR-angiography into artery segments

To achieve sufficient accuracy and robustness, 2D/3D registration methods between DSA and MRA of the cerebral artery require an automatic extraction method that can isolate wanted segments from the cerebral artery tree. Here, we described an automatic segmentation method that divides the cerebral artery tree in time-of-flight magnetic resonance angiography (TOF-MRA) into each artery. This method requires a 3D dataset of the cerebral artery tree obtained by TOF-MRA. The processes of this method are: 1) every branch in the cerebral artery tree is labeled with a unique index number, 2) the 3D center of the Circle of Willis is determined using 2D and 3D templates, and 3) the labeled branches are classified with reference to the 3D territory map of cerebral arteries centered on the Circle of Willis. This method classifies all branches into internal carotid arteries (ICA), basilar artery (BA), middle cerebral artery (MCA), a1 segment of anterior cerebral artery (ACA(A1)), other segments of the anterior cerebral artery (ACA), posterior communication artery (PcomA), and posterior cerebral artery (PCA). In the eleven cases examined, the numbers of correctly segmented pixels in each branch were counted and the percentages based on the total number of pixels of the artery were calculated. Manually classified arteries of each case were used as references. Mean percentages were: ACA, 87.6%; R-ACA(A1), 44.9%; L-ACA(A1), 30.4%; R-MC, 82.4%; L-MC, 79.0%; R-PcomA, 0.5%; L-PcomA, 0.0%; R-PCA, 77.2%; L-PCA, 80.0%; R-ICA, 78.6%; L-ICA, 93.05; BA, 77.1%; and total arteries, 78.9%.

Evaluation of the Effect of Varying MPEG-2 Compression Ratios on Digital Coronary Angiographic Assessment of Stenosis Severity

The purpose of this study is to evaluate the influence of MPEG-2 compression scheme on coronary angiography and to search the highest compression ratio at which no significant effect to accuracy of assessment of stenosis severity occurs. Forty-Four digital cine angiographies were used. Three cardiologists participated in a subjective study in which they read both uncompressed images and compressed images. Furthermore, an objective study was carried out to measure vessel stenosis ratio by using software. The influence of compression was evaluated by kappa statistics in case of subjective study and by both systematic error and random error in case of objective study. Kappa statistics between uncompressed image and compressed image at a ratio of 80:1 was significantly lower than that of other compression ratios such as 40:1. Similar results were obtained in objective evaluation. In this report, the authors provide the baseline for further studies on observer performance for motion images.

PACS in Japan and progress of technology assessment

The statistics of PACS installations in Japan and the progress of key technologies over the past 13 years (1985-98) are described. The total number of installations of more than 557 is comparable with that (517) of hospital information systems (HIS), because advanced electronic technologies have brought a rapid spread of PACS for these 13 years. Examples of large sized PACS in Japan are discussed and a method for integrating HIS and RIS (Radiological Information System) is described. Standardization activities on PACS in Japan such as image data transfer and filing are also introduced. A unique domestic standard in Japan for IS&C (Image Save and Carry) and electronic filing of medical images is presented. The realization of DICOM in Japan is also described. Technology assessment of PACS is discussed in terms of methods and the results of measurement. Examples in the Osaka University Hospital over 6 years (1992-98) are presented. In order to figure out the effectiveness of PACS itself, the HIS/RIS contribution to radiological examination and reporting was measured before PACS was implemented. The total aim of the whole system operation is to maximize the effectiveness of HIS/RIS/PACS integrated each other. The results of time study, character counting in radiological reports, network loading study and other measurements are employed to expand the size of PACS in Osaka University which has 20 terminals at present.

Microcatheter Tip Enhancement in Fluoroscopy: A Comparison of Techniques

We compared three techniques for enhancement of microcatheter tips in fluoroscopic images: conventional subtraction technique (CST); averaged image subtraction technique (AIST), which we have developed; and double average filtering (DAF) technique, which uses nonlinear background estimates. A pulsed fluoroscopic image sequence was obtained as a microcatheter was passed through a carotid phantom that was on top of a head phantom. The carotid phantom was a silicone cylinder containing a simulated vessel with the shape and curvatures of the internal carotid artery. The three techniques were applied to the images of the sequence, then the catheter tip was manually identified in each image, and 100 x 100 pixel images, centered at the indicated microcatheter tip positions, were extracted for the evaluations. The signal-to-noise ratio (SNR) was calculated in each of the extracted images from which the mean value of the SNR and its standard deviation (SD) were calculated for each technique. The mean values and the standard deviations were 4.36 (SD 3.40) for CST, 6.34 (SD 3.62) for AIST, and 3.55 (SD 1.27) for DAF. AIST had a higher SNR compared to CST in almost all frames. Although DAF yielded the smallest mean SNR value, it yielded the best SNR in those frames in which the microcatheter tip did not move between frames. We conclude that AIST provides the best SNR for a moving microcatheter tip and that DAF is optimal for a temporarily stationary microcatheter tip.