Biomedical subjects

Geoffrey D Rubin

Publications and source records attributed to Geoffrey D Rubin.

35 records · Page 2Linked to original sources

PubMed2004

New method of measuring coronary diameter by electron-beam computed tomographic angiography using adjusted thresholds determined by calibration with aortic opacity.

BACKGROUND: In a previous study the adjusted thresholds at which the diameters of coronary arteries determined by enhanced electron-beam computed tomography (CT) scans are equal to the corresponding quantitative coronary angiography measurements were analyzed, and their correlation with maximum CT values for the vessel short axes was determined. A rapid accurate method for such measurements was sought by substituting maximum CT values for the descending aorta in the corresponding axial images for those for the short axes. METHODS AND RESULTS: In 8 patients, 179 sites were measured. Means (+/- SD) of adjusted thresholds and the maximum CT values for vessel short axes and the descending aorta in the corresponding axial images for all vessels were 108 +/-66, 227+/-80, and 363+/-75 Hounsfield Unit (HU), respectively. Adjusted thresholds correlated with the maximum CT values for the corresponding vessel short axes and the descending aorta in the corresponding axial images, with R2=0.55, 0.33, p<0.01, respectively. An abbreviated formula for use of maximum CT values for the descending aorta in the corresponding axial images was y=0.5x-75 (HU) (y= adjusted threshold, x= maximum CT value for the descending aorta in the corresponding axial image). CONCLUSIONS: The abbreviated formula provided a rapid, accurate method for measurements independent of arterial enhancement.

Aorta, Thoracic↗

PubMed2003

Curved-slab maximum intensity projection: method and evaluation.

The authors developed and evaluated a method to produce curved-slab maximum intensity projections (MIPs) through blood vessels that semiautomatically excludes soft tissue and bone. Results obtained with the algorithm were compared with those obtained with rectangular-slab MIPs by using computed tomographic (CT) data from four patients with abdominal aortic aneurysms. Curved-slab MIPs exhibited increased mean vessel-to-perivascular tissue contrast of 55.1 HU (36%), allowed a 10% increase in contrast-to-noise ratio, and decreased apparent vessel narrowing by 0.12-1.09 mm, without increasing processing time. Curved-slab MIPs may also include multiple vessels in a single image, thereby improving interpretation efficiency by reducing the number of MIPs required in these patients from eight to three.

Aged↗

PubMed2003

CT angiography of the thoracic aorta.

Nine years after its introduction, spiral or helical CTA is being embraced as an important noninvasive tool for imaging the thoracic aorta and its branches. The high degree of accessibility and ease with which the studies are performed make it a viable alternative to aortography. Once familiar with the principles of CTA, the acquisition phase of the examination can be completed in as little as 15 minutes. Nevertheless, important challenges remain for CTA. The capabilities of MDCT to acquire thinner sections in shorter scan times have resulted in a veritable explosion of imaging data for radiologists to analyze. In this environment, efficient image processing workstations and software is critical to improving our ability to efficiently interpret these volumetric CT data. Finally, helical CT technology is far from static. Every year, new advances in engineering bring better image quality, improved resolution, and faster scan times. As medical imagers, we must not become complacent but rather constantly challenge ourselves to consider how we might further improve on our utilization of CT equipment to maximize the collection of information relevant to diagnosis and therapy.

Aortic Dissection↗

PubMed2003

3-D imaging with MDCT.

Without doubt, the greatest challenge of multidetector-row CT is dealing with 'data explosion'. For our carotid/intracranial CT angiograms, we routinely have 375 images to review (300 mm coverage reconstructed every 0.8 mm); for aortic studies we have 450-500 images ( approximately 600 mm coverage reconstructed every 1.3 mm); and for a study of the lower extremity inflow and run-off, we may generate 900-1000 transverse reconstructions. While we could reconstruct fewer images for these data, experience with single-detector row CT scanners indicates that longitudinal resolution and disease detection is improved when at least 50% overlap of cross-sections is generated [Radiology 200 (1996) 312]. If we are to optimize our clinical protocols and take full advantage of these CT scanners, we will need to change the way that we interpret, transfer, and store CT data. Film is no longer a viable option. Workstation based review of transverse reconstructions for interpretation is a necessity, but the workstations must improve to provide efficient access to these data, and we must have a way of providing our clinicians with images that can be transported to clinics and the operating room. Alternative visualization and analysis using volumetric tools, including 3-D visualization must evolve from luxury to necessity. We cannot rest on historical precedent to interpret these near isotropically sampled volumetric data using transverse reconstructions alone [Radiology 173 (1989) 527]. Although the tools for volumetric analysis on 3-D workstations have evolved over recent years, they have probably not yet evolved to a level that routine interpretation can be performed as efficiently and accurately as transverse section review. Both hardware and software developments must occur. While current computer workstations and visualization software are certainly adequate for assessing these MDCT data volumetrically, the process is very time consuming. What follows are a description of current workstation capabilities and a brief discussion of where development needs to go to facilitate the complete integration of volumetric analysis into the interpretive process of CT data.

Humans↗

PubMed2003

MDCT imaging of the aorta and peripheral vessels.

Since its clinical introduction in 1991, volumetric CT scanning using spiral or helical scanners has resulted in a revolution for diagnostic imaging. Helical CT has improved over the past 8 years with faster gantry rotation, more powerful X-ray tubes, and improved interpolation algorithms, but the greatest advance has been the recent introduction of multi detector-row CT (MDCT) scanners [J. Comput. Assist. Tomogr. 23 (1999) S83]. Currently capable of acquiring four channels of helical data simultaneously, MDCT scanners have achieved the greatest incremental gain in scan speed since the development of helical CT and have profound implications for clinical CT scanning. Fundamental advantages of MDCT include substantially shorter acquisition times, retrospective creation of thinner or thicker sections from the same raw data, and improved three-dimensional (3-D) rendering with diminished helical artifacts. While these features will likely be important to many applications of CT scanning, including the characterization of focal lung and liver lesions through the creation of thin sections retrospectively, the greatest impact has been on CT angiography. The implication for CT angiography is that scans can be performed approximately three-times faster than is possible with the fastest single-detector CT scanner. For example a 1.25 mm nominal thick section (1.6 mm effective section thickness) can be acquired with a table speed of 9.4 mm/s, and a 2.5 mm nominal thick section (3.2 mm effective section thickness) can be acquired with an 18.8 mm/s table speed. The advantages of MDCT for imaging the vascular system can be broken down into three fundamental improvements over single detector-row CT scanners speed (faster), distance (longer), and section thickness (better). The focus of this article will be how multidetector-row CT technology has substantially improved aortoiliac and lower extremity arterial imaging.

Aortic Dissection↗

PubMed2003

Early experience with computed tomographic angiography in microsurgical reconstruction.

Preoperative angiography is frequently used in the planning of microsurgical reconstruction. However, several potentially devastating complications can result from angiography, including arterial occlusion and pseudoaneurysm. Computed tomographic angiography is a relatively new technique that can provide detailed information about vascular anatomy as well as soft and bony tissue without the risks of traditional angiography. In addition, three-dimensional image reconstruction uniquely demonstrates anatomical relationships among blood vessels, bones, and soft tissue. Fourteen computed tomographic angiograms were obtained in 10 patients undergoing microsurgical reconstruction of the head and neck, lower extremity, or upper extremity. The average patient age was 46.9 years (range, 22 to 67 years). Charges related to the computed tomographic procedure were compared with those of conventional preoperative imaging for microsurgical repair. At our institution, the average computed tomographic angiogram charge was 1140 US dollars, whereas the average charge for traditional arteriography was 3900 US dollars. When compared with intraoperative evaluation, computed tomographic angiograms demonstrated clinically relevant surgical anatomy. No complications were noted for the radiographic procedure or after free flap reconstruction. Computed tomographic angiography provides high-resolution, three-dimensional arterial, venous, and soft-tissue imaging without the risks of traditional angiogram and at a lower cost.

Adult↗

PubMed2003

Semiautomated segmentation of blood vessels using ellipse-overlap criteria: method and comparison to manual editing.

Two-dimensional intensity-based methods for the segmentation of blood vessels from computed-tomography-angiography data often result in spurious segments that originate from other objects whose intensity distributions overlap with those of the vessels. When segmented images include spurious segments, additional methods are required to select segments that belong to the target vessels. We describe a method that allows experts to select vessel segments from sequences of segmented images with little effort. Our method uses ellipse-overlap criteria to differentiate between segments that belong to different objects and are separated in plane but are connected in the through-plane direction. To validate our method, we used it to extract vessel regions from volumes that were segmented via analysis of isolabel-contour maps, and showed that the difference between the results of our method and manually-edited results was within inter-expert variability. Although the total editing duration for our method, which included user-interaction and computer processing, exceeded that of manual editing, the extent of user interaction required for our method was about a fifth of that required for manual editing.

Aneurysm↗

PubMed2003

Coronary artery: quantitative evaluation of normal diameter determined with electron-beam CT compared with cine coronary angiography initial experience.

Eight male heart transplant recipients underwent contrast material-enhanced electron-beam computed tomographic angiography. Coronary artery diameters measured with fixed thresholds and adaptive line density profile (LDP) methods were calculated relative to findings at quantitative coronary angiography. Variation with fixed-threshold methods was significantly greater than that with LDP methods because of variations in vessel enhancement. Thus, more accurate measurements of vessel diameter were obtained with LDP methods.

Cineangiography↗

PubMed2002

CT angiography of the arterial system.

CTA has become an important diagnostic tool in the evaluation of vascular diseases in virtually all parts of the body. Whereas CTA is able to provide images depicting exquisite anatomic detail, careful scanning technique and selection of scan parameters are critical for high quality studies. The choices to be made when prescribing a scan can seem daunting at first, but if one applies the principles outlined previously, CTA can be a relatively easy, fast, and safe diagnostic technique that is effective in the majority of patients with vascular disease.

Angiography↗

PubMed2002

Nature and significance of endoleaks and endotension: summary of opinions expressed at an international conference.

OBJECTIVE: Endoleaks and endotension are critically important complications of some endovascular aortic aneurysm repairs (EVARs). For the resolution of controversial issues and the determination of areas of uncertainty relating to these complications, a conference of 27 interested leaders was held on November 20, 2000. METHODS: These 27 participants (21 vascular surgeons, five interventional radiologists, one cardiologist) had previously answered 40 key questions on endoleaks and endotension. At the conference, these 40 questions and participant answers were discussed and in some cases modified to determine points of agreement (consensus), near consensus (prevailing opinion), or disagreement. RESULTS: Conference discussion added two modified questions for a total of 42 key questions for the participants. Interestingly, consensus was reached on the answers to 24 of 42 or 57% of the questions, and near consensus was reached on 14 of 42 or 33% of the questions. Only with the answers to four of 42 or 10% of the questions was there persistent controversy or disagreement. CONCLUSION: The current endoleak classification system with some important modifications is adequate. Types I and II endoleak occur after 0 to 10% and 10% to 25% of EVARs, respectively. Many (30% to 100%) type II endoleaks will seal and have no detrimental effect, which never or rarely occurs with type I endoleaks. Not all endoleaks can be visualized with any technique, and increased pressure (endotension) can be transmitted through clot. Aneurysm pulsatility after EVAR correlates poorly with endoleaks and endotension. An enlarging aneurysm after EVAR mandates surgical or interventional treatment. These and other conclusions will help to resolve controversy and aid in the management of these vexing complications and should also point the way to future research in this field.

Aortic Aneurysm↗

PubMed2002

Changes in aneurysm volume after endovascular repair of abdominal aortic aneurysm.

OBJECTIVE: The purpose of this study was to define changes in aneurysm volume after endovascular repair of abdominal aortic aneurysm. METHODS: A total of 154 consecutive patients who underwent endovascular repair of abdominal aortic aneurysm with the Medtronic AneuRx stent graft at Stanford University Hospital were evaluated. During a mean follow-up period of 15.8 +/- 11.3 months, serial computerized measurements of aneurysm volume and orthogonal maximal diameter were performed on helical computed tomographic scan data sets and maximal transverse diameter was measured manually from transverse computed tomographic images. Aortoiliac length (renal to hypogastric artery origin) was measured along the median luminal centerline and along the straight line. RESULTS: Aneurysm volume increased immediately after endovascular repair (from 180.2 +/- 69.9 mL to 187.9 +/- 71.6 mL; P <.001), but orthogonal and transverse diameter and aortoiliac length did not change significantly. During the follow-up period, mean volume decreased to 171.9 +/- 70.2 mL (P <.05) and straight-line and centerline aortoiliac length remained unchanged from preoperative values. Overall, volume decreased at a rate of 1.7 +/- 5.9 mL/mo (P <.001). During periods without endoleak, the rate of decrease was 3.2 +/- 5.5 mL/mo (P <.001), and during periods with endoleak, aneurysm volume increased at a rate of 2.0 +/- 5.3 mL/mo (P <.005), without a difference between types of endoleak. Predictive values for the presence of endoleak were similar for transverse and orthogonal diameter and volume. Logistic regression analysis showed volume to be most closely associated with the presence of endoleak. CONCLUSION: Aneurysm volume increases immediately after endovascular repair. After repair, aneurysm volume gradually decreases and aortoiliac length remains unchanged. Changes in volume parallel changes in maximal aneurysm diameter, and their association with the presence of an endoleak does not appear to be appreciably stronger.

Anastomosis, Surgical↗

PubMed2002

Automated generation of curved planar reformations from volume data: method and evaluation.

The authors developed and evaluated a method to automatically create interactive vascular curved planar reformations with computed tomographic (CT) angiographic data. The method decreased user interaction time by 86%, from 15 to 2 minutes. Expert reviewers were asked to indicate their confidence in differentiating automatically created images from clinical-quality manually produced images. The area under the receiver operating characteristic curve was 0.45 (95% CI: 0.39, 0.51), and a test of equivalency indicated that reviewers could not distinguish between images. They also graded image quality as equivalent to that with manual methods and found fewer artifacts on automatically created images. Automatic methods rapidly produce curved planar reformations of equivalent quality with reduced time and effort.

Humans↗

PubMed2002

"Pseudoendoleak"--residual intrasaccular contrast after endovascular stent-graft repair.

PURPOSE: To present a unique demonstration of postoperative perigraft contrast masquerading as an endoleak following endovascular abdominal aortic aneurysm (AAA) repair. CASE REPORT: A 66-year-old man underwent endovascular stent-graft repair of a 4.6-cm infrarenal AAA. The procedure was uncomplicated, and intraoperative completion angiography demonstrated good proximal and distal fixation of the stent-graft without an endoleak. A spiral computed tomographic (CT) angiogram obtained on postoperative day 2 revealed a large amount of extrastent contrast along the posterior aspect of the aneurysm sac. This defect had the appearance of an endoleak, but it was also present on the non-contrast images. A color-flow duplex examination performed on the same day showed a widely patent stent-graft with no evidence of extrastent flow. CONCLUSIONS: Contrast trapped in the aneurysm sac during endovascular aneurysm repair may be misinterpreted as an endoleak on postprocedural CT scans. "Pseudoendoleaks" can be distinguished from true endoleaks by examination of prebolus, noncontrast CT images, as well as by duplex ultrasound scanning.

Aged↗

PubMedDate not supplied

CT angiography of the subclavian artery: utility of curved planar reformations.

Despite advances in the diagnosis and treatment of peripheral vascular occlusive disease, an ever-aging population continues to provide scores of new cases requiring medical care. While traditional angiography has been the mainstay of diagnosis for many years, newer, less invasive techniques such as CT angiography with three-dimensional reformation are rapidly establishing themselves as first-line diagnostic modalities. We present a case of severe left subclavian artery stenosis that demonstrates the utility of curved planar reformation in providing a concise visual summary of the pertinent anatomy and abnormalities.

Angiography↗

PubMedDate not supplied

Computed tomography angiography: state-of-the-art imaging using multidetector-row technology.

Multidetector-row computed tomography (MDCT) is an essential diagnostic modality for many clinical algorithms. This is particularly true with regard to the evaluation of cardiovascular disease. As a result of increased image acquisition speed, improved spatial resolution, and greater scan volume, MDCT angiography (computed tomography angiography [CTA]) has become an excellent noninvasive imaging technique, replacing intra-arterial digital subtraction angiography for most vascular territories. The clinical success of CTA depends on precise synchronization of image acquisition with optimal vascular enhancement. As technology continuously evolves, however, this task can be challenging. It remains important to have a fundamental knowledge of the principles behind technical parameters and contrast medium administration. This article reviews these essential principles, followed by an overview of current clinical applications.

Angiography↗

PubMedDate not supplied

Assessment of global left ventricular function: comparison of cardiac multidetector-row computed tomography with angiocardiography.

OBJECTIVE: Evaluation of left ventricular function using electrocardiogram (ECG)-gated multidetector row CT (MDCT) by using 3 different volumetric assessment methods in comparison to assessment of the left ventricular function by invasive ventriculography. METHODS: Thirty patients with suspected or known coronary artery disease underwent MDCT coronary angiography with retrospective ECG cardiac gating. Raw data were reconstructed at the end-diastolic and end-systolic periods of the heart cycle. To calculate the volumes of the left ventricle, 3 methods were applied: The 3-dimensional data set (3D), the geometric hemisphere cylinder (HC), and the geometric biplane ellipsoid (BE) methods. End-diastolic volumes (EDV), end-systolic volumes (ESV), the stroke volumes (SV), and ejection fractions (EF) were calculated. The left ventricular volumetric data from the 3 methods were compared with measurements from left ventriculography (LVG). RESULTS: The best results were obtained using the 3D method; EDV (r = 0.73), ESV (r = 0.88), and EF (r = 0.76) correlated well with the LVG data. The EDV volumes did not differ significantly between LVG and the 3D method (P = 0.24); however, ESV, SV, and EF differed significantly. The ESV were significantly overestimated (P < 0.01), leading to an underestimation of the SV (P < 0.01) and the EF (P < 0.01). The HC method resulted in the greatest overestimation of the volumes. The EDV and the ESV were 31.8 +/- 37.6% and 136.4 +/- 92.9% higher than the EDV and ESV volumes obtained by LVG. Bland-Altman analysis showed systematic overestimation of the ESV using the HC method. CONCLUSION: MDCT with retrospective cardiac ECG gating allows the calculation of left ventricular volumes to estimate systolic function. The 3D method had the highest correlation with LVG. However, the overestimation of the ESV is significant, which led to an underestimation of the SV and the EF.

Adult↗

PubMedDate not supplied

Image Interpretation Session: Sunday, November 27, 2005.

The Sunday afternoon Image Interpretation Session has been a high point of the annual meeting of the Radiological Society of North America for over 65 years. A panel of five experts has been selected, representing the very best from the fields of neurologic, abdominal, thoracic, pediatric, and musculoskeletal radiology. Each panelist will dazzle us with an insightful analysis of two difficult cases in their area of expertise. The panelists are to be lauded for their bravery in subjecting their diagnostic acumen to the scrutiny of the thousands of radiologists in the audience. The cases, representing a diverse spectrum of diseases and disease manifestations, were selected from recent clinical imaging studies performed at the Stanford University Medical Center or the Lucille Salter Packard Children's Hospital. This session celebrates the skills of diagnostic radiologists worldwide, who are called on daily to amalgamate disparate clinical information with complex imaging data into focused differential diagnoses and effective treatment planning. We hope that these cases will serve to illustrate the central role that expert image interpretation plays in the care of patients. We welcome our audience of RSNA attendees, readers of RadioGraphics, and cyberspace denizens to join with our experts in solving these medical puzzles and to enjoy the excitement of unraveling the unknown.

Adolescent↗