Glenn S. Maitz

Measurement of cerebral blood flow during xenon inhalation as measured by the microspheres method.

Measurements of cerebral blood flow (CBF) were performed using the microsphere technique in non-human primates (baboons) to assess the effect of non-radioactive xenon gas inhalation on CBF. Blood flows in small tissue volumes (approximately 1 cm3) were directly measured before and during the inhalation of xenon/oxygen gas mixtures. The results of these studies demonstrated that when inhaled in relatively high concentrations, xenon gas does increase CBF, but the changes are more global than tissue-specific. The problems and limitations of such evaluations are discussed.

Joint Photographic Experts Group (JPEG) compatible data compression of mammograms

We have developed a Joint Photographic Experts Group (JPEG) compatible image compression scheme tailored to the compression of digitized mammographic images. This includes a preprocessing step that segments the tissue area from the background, replaces the background pixels with a constant value, and applies a noise-removal filter to the tissue area. The process was tested by performing a just-noticeable difference (JND) study to determine the relationship between compression ratio and a readers ability to discriminate between compressed and noncompressed versions of digitized mammograms. We found that at compression ratios of 15∶1 and below, image-processing experts are unable to detect a difference, whereas at ratios of 60∶1 and above they can identify the compressed image nearly 100% of the time. The performance of less specialized viewers was significantly lower because these viewers seemed to have difficulty in differentiating between artifact and real information at the lower and middle compression ratios. This preliminary study suggests that digitized mammograms are very amenable to compression by techniques compatible with the JPEG standard. However, this study was not designed to address the efficacy of image compression process for mammography, but is a necessary first step in optimizing the compression in anticipation of more elaborate reader performance (ROC) studies.

A comparison of two data analyses from two observer performance studies using Jackknife ROC and JAFROC

The authors compared two methodological approaches, Jackknife ROC and JAFROC, in analyzing data ascertained during FROC (free-response receiver operating characteristics) type studies. Observer rating data obtained from two observer performance studies were analyzed. During the first study, seven radiologists interpreted 120 mammography examinations depicting 57 masses under five different conditions with and without the results of computer-aided detection (CAD). In the second study, eight radiologists interpreted 110 examinations depicting 51 masses under six different display conditions with and without CAD results. Readers rated the detection task in a FROC type response. Jackknife ROC (using the software of LABMRMC with the highest rating per case) and JAFROC were used to compute differences, if any, in summary performance levels among all reading modes in each study as well as for all paired data sets. The results of the different analytical approaches are compared. The overall results for all modes were significantly different for the first study (p < 0.05) and not significant (p > 0.05) for the second study using either analytical approach. In the first study, the performance levels represented by three paired data sets were significantly different (p < 0.05) when computed using LABMRMC and four pairs were significantly different (p < 0.05) using JAFROC. In eight of ten pairs, JAFROC produced lower p values than LABMRMC. In the second study, LABMRMC showed no significant differences for any paired data sets and JAFROC showed a significant difference for one pair. In 15 of 16 pairs, p values computed by JAFROC were lower than those computed by LABMRMC.

Simultaneous measurements of cerebral blood flow by the xenon/CT method and the microsphere method. A comparison

Simultaneous measurements of cerebral blood flow have been performed in baboons to assess the correlation between the acute and invasive nondiffusible microsphere technique and the noninvasive xenon-enhanced CT method. Blood flows in small tissue volumes (approximately 1 cm3) were directly compared. The results of these studies demonstrate a statistically significant association between the two methods (P less than .001). Similar correlations were obtained by both the Kendall tau (tau) and the Spearman (r) methods. The problems and limitations of such correlations are discussed.

A simple method for automated lung segmentation in x-ray CT images

We developed and tested an automated scheme to segment lung areas depicted in CT images. The scheme includes a series of six steps. 1) Filtering and removing pixels outside the scanned anatomic structures. 2) Segmenting the potential lung areas using an adaptive threshold based on pixel value distribution in each CT slice. 3) Labeling all selected pixels ingo segmented regions and deleting isolated regions in non-lung area. 4) Labeling and filling interior cavities (e.g., pleural nodules, airway wall, and major blood vessels) inside lung areas. 5) Detecting and deleting the main airways (e.g., trachea and central bronchi) connected to the segmented lung areas. 6) Detecting and separating possible anterior or posterior junctions between the lungs. Five lung CT cases (7-10 mm in slice thickness) with variety of disease patterns were used to train or set up the classification rules in the scheme. Fifty examinations of emphysema patients were then used to test the scheme. The results were compared with the results generated from a semi-automated method with manual interaction by an expert observer. The experimental results showed that the average difference in estimated lung volumes between the automated scheme and manually corrected approach was 2.91%±0.88%. Visual examination of segmentation results indicated that the difference of the two methods was larger in the areas near the apices and the diaphragm. This preliminary study demonstrated that a simple multi-stage scheme had potential of eliminating the need for manual interaction during lunch segmentation. Hence, it can ultimately be integrated into computer schemes for quantitative analysis and diagnosis of lung diseases.

PRELIMINARY CLINICAL EVALUATION OF A HIGH-RESOLUTION TELEMAMMOGRAPHY SYSTEM

RATIONALE AND OBJECTIVES The authors designed, assembled, tested, and clinically evaluated a high-quality, fast, and relatively inexpensive telemammography system. METHODS The authors designed a telemammography system that uses a high-resolution film digitizer and high data compression (> or = 40:1) to send images over regular telephone lines to a high-resolution laser printer that produces images with the look and feel of the original image and can operate in a hub and spokes mode. The authors then evaluated the systems performance. In a preliminary clinical study, interpretations of the laser-printed systems output of 119 cases were compared with the original interpretations, followed by a review of any clinically significant differences. RESULTS With the exception of the laser printer, which is a modified off-the-shelf product, all hardware components of the system are commercially available products. The system digitizes (50 microns pixel size), compresses, transmits, receives, decompresses, and prints a 30 MB mammography file in less than 4 minutes. In the clinical study, there were 13 differences (in 13 cases) in the level of concern or recommendations. Seven were found to be clinically insignificant by a third-party review. The remaining six were reviewed by the original interpreter, and three were determined to be significant enough for further action. All were found to result from intra-reader variability rather than differences in visualization of possible abnormalities. CONCLUSIONS Almost real-time, high-quality telemammography without geographic boundaries is possible with the use of high-level data compression. Telemammography with laser-printed film as the display may make it possible to offer mammographic services in remote locations while using commercially available technology.

A Multisite Telemammography System for Remote Management of Screening Mammography: An Assessment of Technical, Operational, and Clinical Issues

ObjectiveThis paper describes a high-quality, multisite telemammography system to enable “almost real-time” remote patient management while the patient remains in the clinic. One goal is to reduce the number of women who would physically need to return to the clinic for additional imaging procedures (termed “recall”) to supplement “routine” imaging of screening mammography.Materials and MethodsMammography films from current and prior (when available) examinations are digitized at three remote sites and transmitted along with other pertinent information across low-level communication systems to the central site. Images are automatically cropped, wavelet compressed, and encrypted prior to transmission to the central site. At the central site, radiologists review and rate examinations on a high-resolution workstation that displays the images, computer-assisted detection results, and the technologists communication. Intersite communication is provided instantly via a messaging “chat” window.ResultsThe technologists recommended additional procedures at 2.7 times the actual clinical recall rate for the same cases. Using the telemammography system during a series of “off-line” clinically simulated studies, radiologists recommended additional procedures at 1.3 times the actual clinical recall rate. Percent agreement and kappa between the study and actual clinical interpretations were 66.1% and 0.315, respectively. For every physical recall potentially avoided using the telemammography system, approximately one presumed “unnecessary” imaging procedure was recommended.ConclusionRemote patient management can reduce the number of women recalled by as much as 50% without performing an unreasonable number of presumed “unnecessary” procedures.

Multi-site telemammography system: preliminary assessment of technical and operational issues

Our goal was to develop an inexpensive, high-quality, multi-site telemammography system, implemented with low-level data connections that provided a communication link for an “almost real-time” response from a radiologist (central site) to remote “underserved” sites. The remote sites digitize mammographic films using high-resolution, laser digitizers. Images are automatically cropped, compressed (wavelet-based), and encrypted prior to transmission. At the central site images are decrypted, decompressed, unsharp masked, and displayed using automatically determined LUTs. The sites communicate instantly via a “chat box.” Remote sites 1, 2, and 3 are 15, 20, and 90 miles from the central site, respectively, and connected by POTS (sites 1 and 2) and LAN (site 3). Only minimal noticeable difference at compression levels of 50:1 and 75:1 could be identified unless magnified to extreme levels. Two experienced observers rated the LUTs for 200 images as “acceptable” to “excellent.” Average cycle times to digitize, transmit and receive cases (four films each) at 75:1 compression were 5.97, 6.85, and 5.77 min/case from sites 1, 2, and 3, respectively. Unique data-handling schemes significantly decrease the image file size and allow successful transmission in a reliable, timely manner. Over 1000 cases have been transmitted to date. Messaging was found to be easy to use.

X-ray imaging with 2048 x 2048 CCD array

We are investigating a prototype x-ray imaging system in which a scintillating fiberoptic glass plate and/or a fluorescent screen is fiberoptically coupled to a 2048 x 2048 CCD array (Tektronix). The imaging system includes a fiberoptic minifier to increase the imaging field of view to a clinically usable one. The system also allows for cooling of the CCD to reduce the effect of dark noise on image quality and the use of single-stage light amplification to act as a shutter and to provide gain control. Images are software corrected for dark current, individual pixel gain, and geometric distortion. Preliminary results indicate that high quality x-ray imaging can be obtained using this methodology. This paper describes design concepts and configuration of the system as well as characterizations of the initial x-ray images acquired with the camera.

Feature-based differences between mammograms

A novel technique for assessing local and global differences between mammographic images was developed. This method uses correlations between abstract features extracted from corresponding views to compare image properties without resorting to processes that depend on exact geometrical congruence, such as image subtraction, which have a tendency to produce excessive artifact. The method begins by normalizing both digitized mammograms, after which a series of global and local feature filters are applied to each image. Each filter calculates values characterizing a particular property of the given image, and these values, for each property of interest are arranged in a feature vector. Corresponding elements in the two feature vectors are combined to produce a difference vector that indicates the change in the particular properties between images. Features are selected which are expected to be relatively invariant with respect to breast compression.