Biomedical subjects
R N Rankin
Publications and source records attributed to R N Rankin.
A real vessel phantom for imaging experimentation.
Vascular phantoms are used to evaluate imaging techniques such as ultrasound (US), CT, and angiography. They are expected to mimic the vasculature, surrounding tissue, and blood, and therefore must meet specific requirements on the mimicking materials, with respect to x-ray attenuation and acoustic properties (velocity, attenuation). In the past, researchers have used a variety of vessel models, including walled (typically latex tube) and wall-less phantoms (obtained by moulding a lumen in a block of agar). These models lacked the exact geometry of human vessels as well as pathologic features such as plaques and calcifications. To overcome these disadvantages, this paper describes a real vessel phantom for US and x-ray studies. The phantom consists of an agar-filled acrylic box containing a formaldehyde fixed section of a real human vessel (obtained at autopsy) cannulated onto two acrylic tubes. This phantom was evaluated by comparing the images obtained with x-ray angiography, CT, and 3-D B-mode US. The images show good overall correlation based on the location of the geometrical features within the phantom, such as lumen, plaques, and calcifications. Discrepancies, artifacts, and difficulties were minor, and are discussed. The use of a real vessel, with its natural geometry and pathology, makes this phantom attractive for evaluation of imaging techniques including projection radiography, CT and US, and for extending its use to MR and US based flow studies.
Need for radiologists to interpret orthopedic total joint radiographs.
We applaud the aim of Nayak and colleagues: to use our scarce economic resources as judiciously as possible. We have suggested several alternatives that would save more of our scarce health care dollars. We would be delighted to take part in a properly designed prospective randomized trial to address the issues presented in this paper. We believe the literature would be strengthened by the publication of a collegial paper, coauthored by orthopedic and radiology departments, addressing the issue of saving health care dollars by omitting unnecessary or redundant procedures.
Percutaneous gastrostomy in radiologic practice.
Long-term gastrostomy tubes have a well-accepted role in providing nutritional support. Traditionally they have been placed by surgeons and by endoscopists. In the last decade, radiologists have come to play a major role in the placement of gastrostomy and gastrojejunostomy devices, and can usually do so as effectively and at lesser expense. A technique for placement is outlined, with a discussion of patient selection and complications. A review of the literature is provided.
How Canadian radiologists adopt innovations: a survey.
BACKGROUND AND OBJECTIVE: Innovations and practice changes occur frequently in modern radiologic practice. In this study the authors sought to understand the process of adopting an innovation and to define the characteristics of some innovations and the effect of these characteristics on innovation adoption. METHODS: An anonymous mail survey of the membership of the Canadian Association of Radiologists was undertaken to obtain details about the process of adopting an innovation. Information on the perceived characteristics of the innovation was obtained, as well as the perception of change in practice. RESULTS: The survey was sent to 1005 radiologists and was returned by 372 (37.0%), of whom 278 gave information on an innovation adopted in the preceding year. The respondents reported heavy use of textual and other material resources throughout the process of innovation adoption, as well as consultation with colleagues. Continuing medical education (CME) events, in comparison, were little used as information sources. Compatibility of the innovation with current practice and a relative clinical advantage over existing practices were the most important characteristics of the innovations adopted. The complexity, relative financial gain and ability to try the innovation were all less important. CONCLUSIONS: This study confirms a high rate of change in radiologic practice and documents the number and variety of learning resources used in the adoption of change. It is important for CME providers and educators to recognize the relatively low use of CME events in the process of change. Characterization of the innovations indicates concern with the clinical impact of the change and the individual physician's ability to accomplish the change within his or her practice.
Geometric characterization of stenosed human carotid arteries.
RATIONALE AND OBJECTIVES: The geometry of stenosed carotid bifurcations was analyzed to determine average representations for several stenosis grades. METHODS: Film angiograms of 62 patients with internal carotid artery stenoses were digitized. Residual lumen boundaries were manually outlined. The outlines were processed with a computer to extract geometric measurements. The measurements were grouped according to stenosis grade and used to create average representations. RESULTS: Accuracy and precision of the outlining technique were +/- 0.020 common carotid diameters (CCD) and +/- 0.025 CCD, respectively. Maximum narrowing of the internal carotid artery occurred at 0.3 CCD +/- 1.5 (mean +/- standard deviation) distal to the flow divider. The region of significant narrowing extended axially 1.2 CCD +/- 1.0. Poststenotic dilatations were observed, with enlargement of 1.3 +/- 0.7 times the normal diameter of the distal internal carotid artery. A tendency toward smaller bifurcation angles with increasing stenosis severity was observed. CONCLUSION: Three-dimensional geometric models could be created for carotid bifurcations that were disease free (normal) and of arbitrary stenosis grade.
Duplex and color Doppler flow sonography of occlusion and near occlusion of the carotid artery.
PURPOSE: To determine whether color Doppler flow imaging with the use of slow-flow sensitivity improves sensitivity and specificity in the differentiation of occlusion and near occlusion of the internal carotid artery. METHODS: Color Doppler and duplex sonography were performed in symptomatic patients who had angiographically confirmed occlusion and/or near occlusion of the internal carotid artery. The study consisted of two phases: in the first, we assessed the usefulness of color Doppler flow imaging by retrospectively reviewing the records of 35 patients with 36 angiographically confirmed occlusions or near occlusions of the internal carotid artery who were examined with color Doppler flow imaging at our institution during a period of 4 years; in the second phase, we incorporated color Doppler sonography into the routine scanning protocols of 39 patients with 41 occluded or nearly occluded internal carotid arteries seen over a period of 2 1/2 years. RESULTS: Overall, color Doppler imaging correctly showed all 34 of the near occlusions (sensitivity, 100%) and 36 of the 43 occlusions (specificity, 84%). Seven patients with angiographically confirmed occlusion had sonographic findings that suggested near occlusion. In the first phase, eight near occlusions were misinterpreted as occlusions with conventional duplex sonography, but were correctly shown with color Doppler flow imaging. In the second phase, sensitivity increased from 50% to 100% (18 or 18) because of better detection of the nearly occluded lumen. This was at the expense of a decrease in specificity (from 100% to 78%). owing to identification of apparent flow in the internal carotid artery on color Doppler flow images in five of 23 occlusions. CONCLUSION: Because of its ability to depict slow flow, color Doppler imaging with slow-flow sensitivity is superior to conventional duplex sonography for the noninvasive discrimination of occlusion from near occlusion of the internal carotid artery.
Rapid volume flow rate estimation using transverse colour Doppler imaging.
A system is described in which the volume flow rate of blood in a vessel is determined using transverse colour Doppler ultrasound imaging. The system measures rapidly the two-dimensional velocity profile of blood flowing through a vessel. By integration of the measured velocity profiles the volume flow rate of blood in the vessel is obtained. The Doppler angle is obtained from the included angle between two imaging planes, and their respective average measured flows. This technique yields instantaneous and average flow rate in real time, and permits long flow recordings to be made and stored digitally. The error is less than 5% over a 8:1 flow rate range.
Accuracy and prognostic consequences of ultrasonography in identifying severe carotid artery stenosis. North American Symptomatic Carotid Endarterectomy Trial (NASCET) Group.
BACKGROUND AND PURPOSE: The accuracy of routine ultrasonography in detecting severe carotid artery stenosis was evaluated in comparison with cerebral angiography. The precision of ultrasonographic criteria in predicting the risk of stroke was also assessed. METHODS: A total of 1011 symptomatic carotid bifurcations were studied in patients from the North American Symptomatic Carotid Endarterectomy Trial (NASCET). Given that all patients were considered for entry into the trial, the chance of a verification bias affecting the analyses was minimized. The ultrasonographic data consisted of peak systolic velocities and frequency changes from both the internal and common carotid arteries. Angiographic stenosis was calculated as in NASCET. Receiver operating characteristic (ROC) curves were constructed from the ultrasonographic data for the detection of 70% or greater stenosis on the basis of an angiographic assessment. Kaplan-Meier stroke-free survival curves were used to predict the risk of stroke. RESULTS: The areas under the ROC curves ranged from 0.74 to 0.75 (95% confidence interval [CI], 0.69 to 0.79). The sensitivities and specificities ranged from 0.65 to 0.71. The risk of stroke at 18 months declined sharply as the degree of angiographically defined stenosis declined from 99% to 70%. No pattern of decline was apparent on the basis of the ultrasonographic data. CONCLUSIONS: The results indicate that the accuracy of ultrasonography is moderate when flow parameters are used to assess the degree of stenosis. Ultrasonography should be used as a screening tool to exclude patients with no carotid artery disease from further testing. Conventional angiography remains an essential investigation before assigning the risk of stroke and deciding appropriate treatment for extracranial carotid artery disease.
Demonstration of the need for the inclusion of parameter correlations in error estimation for non-linear curve-fitting.
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Pseudoaneurysm after therapeutic knee arthroscopy: imaging findings.
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Poster production by color laser imager.
The scientific poster is an important educational tool at most radiology meetings. The visual impact of the exhibit is important in attracting attention and conveying content to the reader. A new method of designing and producing full-color transilluminated posters in the radiology department using a personal computer and color laser imager is described. The advantages of this approach are author control over the production process and production of a visually interesting exhibit.
Physicians Innovation Awareness Program: helping radiologists learn about innovations.
The Physicians Innovation Awareness Program (PIAP) was designed to study the strategies of Canadian radiologists implementing innovations into their practices and to use the information to design an educational program to help radiologists learn about innovations. Canadian radiologists were asked, by means of a mail survey, for information about innovations in practice adopted in the previous 2 years and planned for the next 2 years. Surveys were sent to the 1077 practising radiologists registered in the Canadian Association of Radiologists (CAR) as of Sept. 30, 1991; 325 (30.2%) responded. Most (281) of the responding radiologists were practising in communities with a population of 50,000 or more; 103 of the 188 respondents for whom faculty status was known were affiliated with a university. Most of the respondents reported that they spent up to 25% of their working time in at least one subspecialty pursuit. From the information in the surveys, an educational strategy was designed to help radiologists in learning about innovations. This program involved special sessions on six selected topics presented at two annual meetings of the CAR, as well as publications, mailings and other lectures. The authors conclude that a specialty society can obtain adequate information from its members to design an educational program to help practitioners in adopting innovations.
Adoption of innovations by Canadian radiologists.
The purpose of this study was to determine the factors that help or hinder the adoption of new procedures and practices by Canadian radiologists. Canadian radiologists were asked, by means of a mail survey, for information about innovations in practice adopted during the previous 2 years or planned for the next 2 years. Surveys were sent to the 1077 practising radiologists registered in the Canadian Association of Radiologists as of Sept. 30, 1991; 325 responded (30.2%). The responses were correlated with demographic information obtained in the same survey and through the Maintenance of Competence Program of the Royal College of Physicians and Surgeons of Canada. Magnetic resonance imaging (MRI) was more likely to be adopted in larger communities (those with a population of more than 500,000), computed tomography in medium-sized and larger communities (more than 100,000), mammography in medium-sized and smaller communities (500,000 or less) and ultrasonography (US) in smaller communities (100,000 or less). Radiologists with a faculty appointment at a university were more likely to adopt MRI and digital imaging, whereas those with no faculty status were more likely to adopt US and structural changes to a practice. The authors conclude that the size of the community in which a practice is located and the practitioner's faculty status both play a role in the adoption of innovations.
Lost gallstones during laparoscopic cholecystectomy: are they really benign?
The long-term effect of stones spilled into the peritoneal cavity during laparoscopic cholecystectomy is unknown. The course of a 58-year-old man who had recurrent right subphrenic abscesses and a right empyema secondary to spilled gallstones during laparoscopic cholecystectomy is described. The authors outline techniques for minimizing the spillage of stones during laparoscopic cholecystectomy: the application of hemoclips, endoloops and sutures, and placement of the necrotic, friable gallbladder in an endoscopic bag immediately upon completion of the dissection, before extraction of the gallbladder. They conclude that spillage of stones during laparoscopic cholecystectomy may lead to serious infection and should be recorded in the operative notes so that stones may be suspected when a patient presents with abdominal infection after laparoscopic cholecystectomy.
Three-dimensional colour Doppler imaging.
We have developed a system to acquire in vivo three-dimensional (3D) colour velocity images of peripheral vasculature. A clinical ultrasound system was modified by mounting the transducer on a motor-driven translation stage, allowing planar ultrasound images to be acquired along a 37 mm long stroke. A 3D velocity image is acquired by digitizing, in synchrony with the cardiac cycle, successive video images as the transducer is moved over the skin surface. 3D images require about 1 min to acquire and 10 min to reconstruct before being viewed interactively. Image acquisition at several points in the cardiac cycle permits a cine-type reconstructed image. Geometrical, temporal and velocity accuracy of the acquisition and reconstruction have been quantified and found not to degrade the image.
Stability studies on chemoembolization mixtures. Dialysis studies of doxorubicin and lipiodol with Avitene, Gelfoam, and Angiostat.
RATIONALE AND OBJECTIVES: Chemoembolization, using a combination of embolic and chemotherapeutic agents, appears to be an effective treatment for hepatocellular carcinoma. Although the postulated mechanism of effectiveness hinges on a prolonged drug delivery, increasing evidence suggests that embolization mixtures are not stable. The objective of this study was to investigate examples of these mixtures. METHODS: Dialysis techniques have been used to examine the pharmacokinetic properties of chemoembolization mixtures that contain doxorubicin, Lipiodol (Guerbet Products, Montreal, Quebec), and the embolizing agents Avitene (Alcon Laboratories Inc., Fort Worth, Texas), Gelfoam (Upjohn, Kalamazoo, MI), and Angiostat (Regional Therapeutic Inc., Pacific Palisades, CA). RESULTS: Lipiodol, Gelfoam, and Avitene, when combined with doxorubicin, had only a small effect on the diffusion of the drug when compared with the diffusion curve of doxorubicin alone. Gelfoam or Avitene produced a thrombus-like consistency when added to a doxorubicin/Lipiodol combination, and an additional decrease in the doxorubicin appearance rate was observed. However, after 6 hours, doxorubicin levels for these mixtures reached control values observed in 3 hours. Angiostat without Lipiodol produced a profound concentration-dependent decrease in the diffusion of doxorubicin. After 9 hours, only 23% of the doxorubicin had been released. CONCLUSION: The strong complexing ability of the embolic agent Angiostat may enable it to be a carrier for doxorubicin and surpass other mixtures currently employed for transcatheter chemoembolization.
Intracavitary aspergilloma: transthoracic percutaneous injection of amphotericin gelatin solution.
For aspergillomas in patients with fibrocavitary lung disease, surgery is often not recommended. Injection or lavage of the cavities with solutions of potassium iodide or antifungal agents has had varying success and requires repeated sessions because of nonretention of the therapeutic agent within the cavity. In three patients with four aspergillomas, the authors used fluoroscopic or computed tomographic (CT) guidance to inject amphotericin in gelatin as a liquid that solidifies within the cavity at body temperature. The patients were followed up with serial chest radiography or CT. The mixture was successfully instilled in every case. Three of the four aspergillomas completely resolved within 3 months or less, with no evidence of recurrence at follow-up of 6-18 months. The remaining aspergilloma decreased in size, but the patient needed pneumonectomy because of recurrent hemoptysis within 6 months of amphotericin injection. Transthoracic instillation of a liquid mixture of amphotericin and gelatin that solidifies rapidly at body temperature may be useful as a one-step treatment for aspergillomas.