Investigating the CT localizer radiograph: acquisition parameters, patient centring and their combined influence on radiation dose.

OBJECTIVE: To systematically investigate the effect of CT localizer radiograph acquisition on the tube current modulation and thus radiation dose of the subsequent diagnostic scan. METHODS: Localizer radiographs of an abdominal section CT phantom were taken, and the resulting volume CT dose index (CTDIvol) for the diagnostic scan was recorded. Variables included tube potential, the phantom's alignment within the CT scanner gantry in both the vertical and horizontal directions and the X-ray source angle at which the localizer was acquired. RESULTS: Diagnostic scan CTDIvol decreased with increasing tube potential. Vertical (table height) movement was found to affect radiation dose more than horizontal movement, with ±50 mm table movement resulting in a standard deviation in the diagnostic scan CTDIvol of 4.4 mGy, compared with 2.5 mGy with ±50 mm horizontal movement. Correspondingly, localizer angles of 90° or 270° (3 o'clock and 9 o'clock X-ray source positions) were less sensitive overall to alignment errors, with a standard deviation of 2.5 mGy, compared with a 0° or 180° angle, which had a standard deviation of 3.8 mGy. CONCLUSION: To achieve a consistently optimized radiation dose, the localizer protocol should be paired with the diagnostic acquisition protocol. A final acquisition angle of 90° should be used when possible to minimize dose variation resulting from alignment errors. ADVANCES IN KNOWLEDGE: Localizer parameters that affect radiation output were identified for this scanner system. The importance of tube potential and acquisition angle was highlighted.

A hierarchical storage management (HSM) scheme for cost-effective on-line archival using lossy compression.

A hierarchical storage management (HSM) scheme for cost-effective on-line archival of image data using lossy compression is described. This HSM scheme also provides an off-site tape backup mechanism and disaster recovery. The full-resolution image data are viewed originally for primary diagnosis, then losslessly compressed and sent off site to a tape backup archive. In addition, the original data are wavelet lossy compressed (at approximately 25:1 for computed radiography, 10:1 for computed tomography, and 5:1 for magnetic resonance) and stored on a large RAID device for maximum cost-effective, on-line storage and immediate retrieval of images for review and comparison. This HSM scheme provides a solution to 4 problems in image archiving, namely cost-effective on-line storage, disaster recovery of data, off-site tape backup for the legal record, and maximum intermediate storage and retrieval through the use of on-site lossy compression.

Computers in imaging and health care: now and in the future.

Early picture archiving and communication systems (PACS) were characterized by the use of very expensive hardware devices, cumbersome display stations, duplication of database content, lack of interfaces to other clinical information systems, and immaturity in their understanding of the folder manager concepts and workflow reengineering. They were implemented historically at large academic medical centers by biomedical engineers and imaging informaticists. PACS were nonstandard, home-grown projects with mixed clinical acceptance. However, they clearly showed the great potential for PACS and filmless medical imaging. Filmless radiology is a reality today. The advent of efficient softcopy display of images provides a means for dealing with the ever-increasing number of studies and number of images per study. Computer power has increased, and archival storage cost has decreased to the extent that the economics of PACS is justifiable with respect to film. Network bandwidths have increased to allow large studies of many megabytes to arrive at display stations within seconds of examination completion. PACS vendors have recognized the need for efficient workflow and have built systems with intelligence in the management of patient data. Close integration with the hospital information system (HIS)-radiology information system (RIS) is critical for system functionality. Successful implementation of PACS requires integration or interoperation with hospital and radiology information systems. Besides the economic advantages, secure rapid access to all clinical information on patients, including imaging studies, anytime and anywhere, enhances the quality of patient care, although it is difficult to quantify. Medical image management systems are maturing, providing access outside of the radiology department to images and clinical information throughout the hospital or the enterprise via the Internet. Small and medium-sized community hospitals, private practices, and outpatient centers in rural areas will begin realizing the benefits of PACS already realized by the large tertiary care academic medical centers and research institutions. Hand-held devices and the Worldwide Web are going to change the way people communicate and do business. The impact on health care will be huge, including radiology. Computer-aided diagnosis, decision support tools, virtual imaging, and guidance systems will transform our practice as value-added applications utilizing the technologies pushed by PACS development efforts. Outcomes data and the electronic medical record (EMR) will drive our interactions with referring physicians and we expect the radiologist to become the informaticist, a new version of the medical management consultant.

Relevant priors prefetching algorithm performance for a picture archiving and communication system.

Proper prefetching of relevant prior examinations from a picture archiving and communication system (PACS) archive, when a patient is scheduled for a new imaging study, and sending the historic images to the display station where the new examination is expected to be routed and subsequently read out, can greatly facilitate interpretation and review, as well as enhance radiology departmental workflow and PACS performance. In practice, it has proven extremely difficult to implement an automatic prefetch as successful as the experienced fileroom clerk. An algorithm based on defined metagroup categories for examination type mnemonics has been designed and implemented as one possible solution to the prefetch problem. The metagroups such as gastrointestinal (GI) tract, abdomen, chest, etc, can represent, in a small number of categories, the several hundreds of examination types performed by a typical radiology department. These metagroups can be defined in a table of examination mnemonics that maps a particular mnemonic to a metagroup or groups, and vice versa. This table is used to effect the prefetch rules of relevance. A given examination may relate to several prefetch categories, and preferences are easily configurable for a particular site. The prefetch algorithm metatable was implemented in database structured query language (SQL) using a many-to-many fetch category strategy. Algorithm performance was measured by analyzing the appropriateness of the priors fetched based on the examination type of the current study. Fetched relevant priors, missed relevant priors, fetched priors that were not relevant to the current examination, and priors not fetched that were not relevant were used to calculate sensitivity and specificity for the prefetch method. The time required for real-time requesting of priors not previously prefetched was also measured. The sensitivity of the prefetch algorithm was determined to be 98.3% and the specificity 100%. Time required for on-demand requesting of priors was 9.5 minutes on average, although this time varied based on age of the prior examination and on the time of day and database traffic. A prefetch algorithm based on metatable examination mnemonic categories can pull the most appropriate relevant priors, reduce the number of missed relevant priors, and therefore reduce the time involved for the manual task of on-demand requests of priors. Network and database traffic can be reduced as well by decreasing the number of priors selected from the archive and subsequently transmitted to the display stations, through elimination of transactions on examinations not relevant to the current study.

PACS databases and enrichment of the folder manager concept.

Current challenges facing picture archiving and communication systems (PACS) center around database design and functionality. Workflow issues and folder manager concepts such as autorouting, prefetching, hanging protocols, and hierarchical storage management are driven by a properly designed database that ultimately directly impacts the clinical utility of a PACS. The key issues in PACS database design that enable radiologist-friendly, cost-effective, and data-secure systems will be discussed, including database difficulties of the DICOM standard, HIS/RIS/PACS (hospital information system/radiology information system) connectivity, and database issues in data acquisition, data dissemination, and data display.

Finding-specific display presets for computed radiography soft-copy reading.

Much work has been done to optimize the display of cross-sectional modality imaging examinations for soft-copy reading (i.e., window/level tissue presets, and format presentations such as tile and stack modes, four-on-one, nine-on-one, etc). Less attention has been paid to the display of digital forms of the conventional projection x-ray. The purpose of this study is to assess the utility of providing presets for computed radiography (CR) soft-copy display, based not on the window/level settings, but on processing applied to the image optimized for visualization of specific findings, pathologies, etc (i.e., pneumothorax, tumor, tube location). It is felt that digital display of CR images based on finding-specific processing presets has the potential to: speed reading of digital projection x-ray examinations on soft copy; improve diagnostic efficacy; standardize display across examination type, clinical scenario, important key findings, and significant negatives; facilitate image comparison; and improve confidence in and acceptance of soft-copy reading. Clinical chest images are acquired using an Agfa-Gevaert (Mortsel, Belgium) ADC 70 CR scanner and Fuji (Stamford, CT) 9000 and AC2 CR scanners. Those demonstrating pertinent findings are transferred over the clinical picture archiving and communications system (PACS) network to a research image processing station (Agfa PS5000), where the optimal image-processing settings per finding, pathologic category, etc, are developed in conjunction with a thoracic radiologist, by manipulating the multiscale image contrast amplification (Agfa MUSICA) algorithm parameters. Soft-copy display of images processed with finding-specific settings are compared with the standard default image presentation for 50 cases of each category. Comparison is scored using a 5-point scale with the positive scale denoting the standard presentation is preferred over the finding-specific processing, the negative scale denoting the finding-specific processing is preferred over the standard presentation, and zero denoting no difference. Processing settings have been developed for several findings including pneumothorax and lung nodules, and clinical cases are currently being collected in preparation for formal clinical trials. Preliminary results indicate a preference for the optimized-processing presentation of images over the standard default, particularly by inexperienced radiology residents and referring clinicians.

Continuing quality improvement procedures for a clinical PACS.

The University of California at San Francisco (USCF) Department of Radiology currently has a clinically operational picture archiving and communication system (PACS) that is thirty-five percent filmless, with the goal of becoming seventy-five percent filmless within the year. The design and implementation of the clinical PACS has been a collaborative effort between an academic research laboratory and a commercial vendor partner. Images are digitally acquired from three computed radiography (CR) scanners, five computed tomography (CT) scanners, five magnetic resonance (MR) imagers, three digital fluoroscopic rooms, an ultrasound mini-PACS and a nuclear medicine mini-PACS. The DICOM (Digital Imaging and Communications in Medicine) standard communications protocol and image format is adhered to throughout the PACS. Images are archived in hierarchical staged fashion, on a RAID (redundant array of inexpensive disks) and on magneto-optical disk jukeboxes. The clinical PACS uses an object-oriented Oracle SQL (systems query language) database, and interfaces to the Radiology Information System using the HL7 (Health Languages 7) standard. Components are networked using a combination of switched and fast ethernet, and ATM (asynchronous transfer mode), all over fiber optics. The wide area network links six UCSF sites in San Francisco. A combination of high and medium resolution dual-monitor display stations have been placed throughout the Department of Radiology, the Emergency Department (ED) and Intensive Care Units (ICU). A continuing quality improvement (CQI) committee has been formed to facilitate the PACS installation and training, workflow modifications, quality assurance and clinical acceptance. This committee includes radiologists at all levels (resident, fellow, attending), radiology technologists, film library personnel, ED and ICU clinician end-users, and PACS team members. The CQI committee has proved vital in the creation of new management procedures, providing a means for user feedback and education, and contributing to the overall acceptance of, and user satisfaction with the system. Well developed CQI procedures have been essential to the successful clinical operation of the PACS as UCSF Radiology moves toward a filmless department.

Assessment of trabecular structure using high resolution CT images and texture analysis.

PURPOSE: Our goal was to use high resolution (HR) CT images combined with texture analysis to investigate the trabecular structure of human vertebral specimens and to compare these techniques with bone mineral density (BMD) in the prediction of bone strength. METHOD: HR CT images with a slice thickness of 1 mm were obtained of 28 bone cubes. Four different groups of texture analysis techniques were used to assess these images. In addition, quantitative CT (QCT) was performed and elastic modulus (EM) was determined biomechanically. RESULTS: R2 between EM and BMD was 0.78 (p < 0.01). R2 values for EM versus most of the texture measures were also significant. Texture measures in addition to measures of BMD in a multivariate regression model significantly increased R2 up to 0.87. CONCLUSION: In an experimental setting, texture parameters calculated using HR CT images correlated significantly with EM. Combining texture measures with BMD improved the prediction of EM significantly.

Focal liver lesions: characterization with nonenhanced and dynamic contrast material-enhanced MR imaging.

PURPOSE: To evaluate prospectively the diagnostic accuracy of non-enhanced and gadolinium-enhanced magnetic resonance (MR) imaging in characterization of hepatic lesions. MATERIALS AND METHODS: Fifty-five patients with benign and 52 patients with malignant focal liver lesions underwent examination at 1.5 T that comprised nonenhanced and dynamic contrast material-enhanced images. Four experienced radiologists independently read the different sets of images without and with knowledge of clinical history. RESULTS: Receiver operating characteristic analysis showed that dynamic contrast-enhanced MR imaging added information to nonenhanced MR studies and thereby improved distinction between benign and malignant lesions (P < .05). Knowledge of clinical data further improved lesion characterization with nonenhanced and combined nonenhanced and contrast-enhanced MR imaging (P < .05). CONCLUSION: Dynamic contrast-enhanced MR imaging is a useful adjunct for characterization of hepatic lesions. Knowledge of clinical history still has a decisive effect on interpretation of MR images of the liver.

A survey of radiation oncologists regarding their radiation physics instruction.

The American Association of Physicists in Medicine, Committee on Training of Radiologists conducted a survey of radiation oncologists requesting information regarding their radiation oncology physics training. General questions were asked of the oncologist regarding their radiation oncology practice such as number of oncologists, number of new patients treated, and the size and type of facility in which the practice is located. The oncologist also responded to questions regarding their educational background. The survey requested the radiation oncologists to answer questions regarding the adequacy and importance of their training in specific areas of radiation physics. The responders indicated that the importance of most physics topics in their clinical practice corresponded to the level of their understanding. The survey indicated that for most radiation oncologists their physics instruction was an important and interesting part of their residency program.

Perfusion quantitation by ultrafast computed tomography.

Flow measurements can be made with computed tomography (CT) scanners using iodinated, nonionic contrast media as a first-pass indicator. Ultrafast CT (UFCT) is an ideal machine to make these measurements because of its short scan time (50 mseconds) and interscan delay (< or = 0.6 seconds). Additionally, UFCT can acquire data at up to eight cross-sectional levels without moving the patient. Direct application of indicator dilution principles permit measurement of cardiac output and has been validated in both animals and humans. However, measurement of myocardial perfusion, an initial design goal of the UFCT scanner, has been difficult. Experiments in animals have consistently underestimated flow at high flow rates. Methods to improve accuracy include better accounting for tissue blood volume and minimizing image artifacts.

Enteroclysis and small bowel series: comparison of radiation dose and examination time.

Respective radiation doses and total examination and fluoroscopy times were compared for 50 patients; 25 underwent enteroclysis and 25 underwent small bowel series with (n = 17) and without (n = 8) an examination of the upper gastrointestinal (GI) tract. For enteroclysis, the mean skin entry radiation dose (12.3 rad [123 mGy]) and mean fluoroscopy time (18.4 minutes) were almost 1 1/2 times greater than those for the small bowel series with examination of the upper GI tract (8.4 rad [84 mGy]; 11.4 minutes) and almost three times greater than those for the small bowel series without upper GI examination (4.6 rad [46 mGy]; 6.3 minutes). However, the mean total examination completion time for enteroclysis (31.2 minutes) was almost half that of the small bowel series without upper GI examination (57.5 minutes) and almost four times shorter than that of the small bowel series with upper GI examination (114 minutes). The higher radiation dose of enteroclysis should be considered along with the short examination time, the age and clinical condition of the patient, and the reported higher accuracy when deciding on the appropriate radiographic examination of the small bowel.

Left atrial volume determination by biplane two-dimensional echocardiography: validation by cine computed tomography.

Left atrial (LA) volume measurements have been made by the application of the method of discs (modified Simpson's rule) to orthogonal biplane atrial echocardiographic images. Validation of the technique has been suboptimal due to deficiencies of the reference standard, levophase angiography. To define the accuracy of echocardiography, we compared LA end-systolic volume by echocardiography in 27 patients with volumes by cine computed tomography (Cine CT), a highly accurate and validated method of measuring cardiac chambers. Echocardiographic tracings were made in the apical long-axis two- and four-chamber views. In patients with atria less than 300 ml, 14 had echoes performed prospectively, with optimization of LA size, while the remaining 10 were analyzed retrospectively. The volume of each slice was calculated and was then summated to obtain total volume. The correlation coefficient between two-dimensional echocardiography and Cine CT was r = 0.98, and it was r = 0.82 when patients with atria greater than 300 ml (n = 3) were excluded. Echocardiography underestimated Cine CT measurements by 23%. The slope of the prospective group was closer to unity than the slope of the retrospective group (p less than 0.001), and the correlation with Cine CT was slightly better for the prospective group (r = 0.88 versus r = 0.77). LA volume by two-dimensional echocardiography correlates closely with Cine CT, a more accurate method of volume determination, and gives valid measurements of LA volume. Efforts to maximize LA size during scanning limit inaccuracies of echocardiographic measurements of the left atrium.

Varying tracheal cross-sectional area during respiration in infants and children with suspected upper airway obstruction by computed cinetomography scanning.

An ultrafast cinetomography computed tomographic scanner (cine-CT) was used to evaluate infants and children (n = 15) with suspected obstruction of the larynx or trachea. One scan sequence provided a single image at each of eight cross-sectional levels (volume-mode study). Each study, lasting 224 ms, covered the distance between the supraglottic area and the carina. Each patient also underwent a "dynamic" study at a specific level of interest determined from the volume-mode study. Forty images within 2.3 s covered at least one respiratory cycle. The images were displayed as a closed-loop movie and dynamic changes in laryngeal and tracheal caliber with respiration were monitored and quantitated. Tracheal boundaries were outlined either by a trackball-guided cursor (freehand) or semi-automated computer edge detection, and cross-sectional areas and diameters were determined. Reproducibility was tested among three investigators' freehand drawings and two automated computer drawings, at the same and at varying image intensities. The coefficient of variation for the computer-assisted records (0.2%) was smaller than for the best freehand drawing (1.5%). Tracheal diameters were reproducible, but with greater intra-individual investigator variability. Four normal tracheas had close to published measurements with conventional CT scanners. Cine-CT gives objective tracheal dimensions and their variation during respiration; it provides good anatomical detail above the carina, and also of the extra- and intra-thoracic vessels if injected with contrast medium.

Evaluation of ultrafast CT scanning of the adult abdomen.

Various measures of image quality were compared from adult abdomen scans obtained with a subsecond computed tomographic (CT) scanner (Imatron Ultrafast C-100) and a conventional third-generation whole-body scanner (GE9800). Forty images from 13 patients scanned within 2 hours of each other on both scanners were evaluated with techniques standardized as much as possible for CT exposure factors and contrast enhancement. Two observers in consensus evaluated matched anatomic levels using standard window width and level settings. Each image was graded on a scale of 1 (worst) to 5 (best) for spatial resolution, image noise, and presence and type of artifacts. Overall image quality also was graded. Averaged scores were compared between the two scanners. In all categories, scores were slightly higher for the GE9800. However, the differences in spatial resolution, presence of artifacts, overall image quality were not significant using the sign test. There was a significant difference, in favor of the GE9800, in image noise. The types of artifacts differed; the GE9800 produced more motion artifacts from bowel and surgical clips and the Imatron C-100 produced more rib shadow artifacts projecting on the liver and spleen. While the GE9800 produced abdominal images of slightly superior quality in adults, the Imatron Ultrafast C-100 was shown to produce images suitable for routine abdominal imaging in adults.

Determination of left ventricular mass with ultrafast CT and two-dimensional echocardiography.

Conventional methods for determining mass of the left ventricle (LV) require geometric assumptions. Eleven patients were studied with ultrafast computed tomography (CT) and with two-dimensional echocardiography (2-D echo) for calculation of LV mass. With ultrafast CT, calculations were performed on end-systole images and end-diastole images for each patient. Comparisons of the results from ultrafast CT with those from 2-D echo were made with linear, Spearman rank, and interclass correlation coefficients, as well as with slope and intercept values of regression lines. Adequate ultrafast CT and 2-D echo studies were obtained in nine of the 11 patients. After the systolic and diastolic ultrafast CT determinations of LV mass were averaged, the results demonstrated excellent agreement with the 2-D echo determinations (slope = 1.0 +/- 0.20, r = .89, P less than .002).

Measurement of regional myocardial blood flow in dogs by ultrafast CT.

We measured blood flow within each of eight segments of the left ventricular myocardium in dogs by an Ultrafast CT scanner. The results were compared with flow determined by radiolabeled microspheres. Computed tomography (CT) flow was measured by an intravenous injection of nonionic contrast agent done simultaneously with the left atrial injection of microspheres. We calculated flow from the CT data by obtaining CT number versus time curves for regions of interest in the myocardium and by using a formula that related flow to both the time and value of the peak enhancement. Measurements were obtained in five dogs at rest and during hyperperfusion induced by chromonar. Based on 169 regional measurements, the Ultrafast CT and microsphere-determined flows correlated moderately (r = 0.68) over a range of 0.4 to 8 mL/min/g. However, when the data were divided into resting and hyperperfusion (ie, 20 to 30 minutes after the injection of the chromonar) states, a significant (P less than .001) increase in regional flow was determined from the CT measurements. The conclusion was that Ultrafast CT can distinguish between low and high myocardial flow states in dogs and has considerable potential for evaluating coronary flow reserve.

Functional dynamics of the knee joint by ultrafast, cine-CT.

An ultrafast, cine-CT scanner was used to demonstrate the differential mobility of the lateral and medial femoral condyles on their respective tibial plateaus in cadaver knees and to show the kinematic type of motion of the knee joint. Current imaging techniques cannot accomplish this because they do not perform combined quantitative, tomographic, and dynamic studies. Accordingly, this preliminary report presents the data from cine-CT scans of 12 normal intact adult cadaver knees. Scans were obtained at the rate of 14 or 17 per second at 50 or 100 ms exposures through midsagittal planes of the medial and lateral condyles and intercondylar notch. The cine-CT scans were displayed on a CRT and analyzed as closed-loop movies and as isolated images. Each cadaver femoral condyle demonstrated a different combined rolling and gliding motion. Preliminary results on the cadaver knee suggest the lateral femoral condyle moved 2.3 times further on the tibial plateau than its medial counterpart. The percentage of rolling for the lateral condyle was 43%-49%; the percentage of gliding was 51%-57%, with a ratio of rolling to gliding of 1:1.2. The percentage of rolling for the medial condyle was 16%-26%; the percentage of gliding 74%-84% with a ratio of rolling to gliding of 1:3.8. The femoral condyles, tibia, and cruciate ligaments acted as a crossed four-bar linkage in concordance with kinematic theory. The applicability of the cadaver knee results to patient dynamics and diagnosis cannot be determined from this study and awaits further investigations on the in vivo knee. However, ultrafast cine-CT demonstrated the complex knee motion in the cadaver knee joint.