Biomedical subjects
Publications and source records attributed to C M Strother.
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OBJECTIVE: To demonstrate spontaneous regression of large, clinically symptomatic optic pathway gliomas in patients with and without neurofibromatosis type 1 (NF-1). METHODS: Patient cases were collected through surveys at 2 consecutive annual meetings of the North American Neuro-Ophthalmology Society (NANOS) and through requests on the NANOSNET Internet listserv. Serial documentation of tumor signal and size, using magnetic resonance imaging in 11 patients and computed tomography in 2 patients, was used to evaluate clinically symptomatic optic pathway gliomas. All tumors met radiologic criteria for the diagnosis of glioma and 4 patients had biopsy confirmation of their tumors. In 3 patients, some attempt at therapy had been made many years before regression occurred. In one of these, radiation treatment had been given 19 years before tumor regression, while in another, chemotherapy had been administered 5 years before signal changes in the tumor. In the third patient, minimal surgical debulking was performed 1 year before the tumor began to shrink. RESULTS: Spontaneous tumor shrinkage was noted in 12 patients. Eight patients did not have NF-1. In an additional patient without NF-1, a signal change within the tumor without associated shrinkage was detected. Tumor regression was associated with improvement in visual function in 10 of 13 patients, stability of function in 1, and deterioration in 2. CONCLUSIONS: Large, clinically symptomatic optic gliomas may undergo spontaneous regression. Regression was seen in patients with and without NF-1. Regression may manifest either as an overall shrinkage in tumor size, or as a signal change on magnetic resonance imaging. A variable degree of improvement in visual function may accompany regression. The possibility of spontaneous regression of an optic glioma should be considered in the planning of treatment of patients with these tumors.
BACKGROUND AND PURPOSE: Many wide-necked aneurysms are difficult or impossible to treat with the Guglielmi detachable coil (GDC). The purpose of this study was to evaluate the use of a neck bridging device, the TriSpan coil, in combination with standard GDCs for the treatment of wide-necked aneurysms in an experimental canine aneurysm model. METHODS: Of 24 experimental aneurysms in 12 animals, 19 (7 lateral and 12 terminal) were treated with the TriSpan coil in conjunction with standard GDCs. Digital subtraction angiography (DSA) was performed on all animals immediately after treatment. In 6 animals, follow-up DSA and histological evaluation were performed 4 weeks after treatment. In the remaining 6, DSA was done at both 90 and 180 days after treatment. Histological evaluation was done immediately after the 180-day angiographic evaluation. RESULTS: The TriSpan was easy to use in conjunction with the standard GDC. Because of their geometry, some lateral aneurysms were difficult or impossible to treat with this device. Greater than 90% aneurysm occlusion was obtained in all 19 aneurysms. In no instance was there evidence of coil migration, herniation, or aneurysm recanalization. Histological evaluation of the tissue surrounding the TriSpan coil showed tissue responses similar to that seen with standard GDCs. CONCLUSIONS: These results show that the TriSpan coil in conjunction with standard GDCs can be used safely and effectively for the treatment of wide-necked aneurysms in this canine model. Positioning and deployment of the neck bridge in aneurysms having an acute angle with the long axis of their parent artery are difficult or impossible. It is likely that this device, used in conjunction with the standard GDC, will allow treatment of some wide-necked aneurysms that are not treatable with the GDC alone.
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BACKGROUND AND PURPOSE: Treatment of ruptured aneurysms with Guglielmi detachable coils (GDCs) has been shown to prevent repeat bleeding. To assess whether GDC coiling alters aneurysmal pressure, we measured intraaneurysmal pressure in two canine types of carotid artery aneurysms before and after GDC placement. METHODS: A 0.014-inch guidewire with a pressure transducer was inserted into parent arteries and domes of surgically created aneurysms. Intravascular static pressures were recorded before and during saline power injections (10, 20, and 30 mL over 1 and 2 s), before and after GDC placement. Common femoral arterial pressure was monitored. RESULTS: Saline power injections reproducibly and abruptly increased pressure in parent arteries and aneurysms. Mean intraaneurysmal pressure varied (18 +/- 4 [10 mL] to 75 +/- 15 mm Hg [30 mL]), independent of injection duration. Intraaneurysmal baseline pressures were higher after GDC placement (111 +/- 10 versus 93 +/- 15 mm Hg; P =.05). Aneurysmal pressure increases with saline injections were slightly higher after GDC placement, which dampened intraaneurysmal pressure amplitude at baseline (26.5 +/- 5.6 versus 19.6 +/- 7.4 mm Hg; P =.003) and during hypertension (25.3 +/- 5.4 versus 19.8 +/- 7.5 mm Hg, P =.002). The pressure increase slope with saline injection was delayed with GDC placement (0.24 +/- 0.1 versus 0.38 +/- 0.19 s; P <.001). CONCLUSION: Graded saline power injections into parent arteries can rapidly increase intraaneurysmal pressure. GDC treatment did not attenuate mean intraaneurysmal pressures, but both dampened the pressure amplitude and delayed pressure increases during locally induced hypertension.
PURPOSE: To test the hypothesis that real-time magnetic resonance (MR) imaging-guided passive catheter tracking is feasible with use of dilute gadolinium (Gd)-filled catheters, to determine the optimal Gd concentration required for tracking, and to measure catheter tip tracking accuracy. MATERIALS AND METHODS: The authors tested a real-time, T1-weighted, two-dimensional, spoiled gradient-recalled echo MR imaging sequence suitable for tracking catheters. In a yogurt phantom, the authors placed 5-F catheters filled with 2%-12% Gd solutions. MR imaging was performed with and without use of a projection dephaser that suppressed background signal. The authors measured signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and enhancement ratio to determine the optimal Gd concentration for catheter depiction. Catheter tip tracking accuracy was measured in an acrylic phantom with use of linear regression analysis, with goodness of fit assessed statistically with the F test. RESULTS: Peak catheter SNR, CNR, and enhancement ratios were obtained with 4%-6% Gd concentrations. Tip tracking accuracy was determined to be +/- 0.41 mm (R2 = 0.99; P < .0001). MR imaging reconstructions were displayed up to 3.1 frames/sec. CONCLUSIONS: Accurate MR imaging-guided passive catheter tracking was feasible in real-time with use of dilute Gd-filled catheters. This technique may have application in MR imaging-guided endovascular procedures.
PURPOSE: To test the hypothesis that magnetic resonance (MR) imaging can guide the percutaneous treatment of renal artery stenosis in a pig model. MATERIALS AND METHODS: Ameroid constrictors were surgically placed around six renal arteries in four pigs. After 30-36 days, all stenoses were documented by conventional x-ray aortograms. MR-guided renal angioplasty was attempted for three stenoses. For these pigs, MR angiography was performed with use of contrast-enhanced three-dimensional (3D) techniques. The authors visualized catheters by filling them with dilute 4% gadolinium and imaging with two-dimensional (2D) and 3D MR fast spoiled gradient recalled echo techniques. Under MR guidance, the authors advanced a selective catheter into the affected renal artery and crossed the stenosis with a nitinol guide wire. Angioplasty was performed with a balloon catheter filled with dilute gadolinium. Stenosis and luminal diameter measurements were compared before and after angioplasty. RESULTS: After ameroid constrictor placement, four significant stenoses, one mild stenosis, and one occlusion developed. Under MR guidance, the authors achieved technical success in performing three of three (100%) attempted dilations. After MR-guided angioplasty, the mean reduction in stenosis was 35% and the mean increase in luminal diameter was 1.6 mm. CONCLUSION: Use of MR guidance for the angioplasty of renal artery stenosis in pigs is feasible.
PURPOSE: To evaluate the feasibility of using magnetic resonance (MR) imaging to guide and monitor endovascular therapeutic procedures. MATERIALS AND METHODS: Endovascular therapeutic procedures were performed with MR imaging guidance in eight dogs by using a 1.5-T MR unit with echo-planar imaging capabilities. Carotid arterial aneurysms were surgically created in four dogs. The ability to depict, track, and position catheters, guide wires, and Guglielmi detachable coils was assessed. Catheters were first positioned with fluoroscopic guidance. Tracking and depiction were achieved with MR imaging by using commercially available catheters filled with a gadopentetate dimeglumine solution and a fast, two-dimensional, time-resolved, variable-rate k-space sampling technique. RESULTS: When either a catheter or the coaxial space between a catheter and a guide wire was filled with a solution of gadopentetate dimeglumine, catheter movement was always depicted. In the animals with aneurysms, it was possible to depict movement of a catheter into and out of the aneurysm. This was achieved by superimposing reconstructed images obtained during catheter movement onto a previously acquired MR angiogram ("road map"). Prototype Guglielmi detachable coils were successfully positioned and detached. Aneurysm obliteration was monitored with the acquisition of new road map images. CONCLUSION: The results demonstrate the feasibility of using MR imaging to guide endovascular therapeutic procedures.
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Extracranial-intracranial (EC-IC) bypass may be necessary to facilitate treatment of unclippable posterior circulation fusiform aneurysms. Although intraoperative digital subtraction angiography (DSA) allows assessment of graft patency, this technique, because of difficulties inherent in performing selective catheterization and angiography in the operating room, has limitations. Duplex sonography, in contrast, is easily performed, and provides information regarding graft patency and blood flow direction during EC-IC bypass procedures. This latter information proved useful in determining the time of parent artery occlusion after two EC-IC bypass procedures performed for treatment of a fusiform midbasilar artery aneurysm.
BACKGROUND AND PURPOSE: Previous studies have depicted arterial and aneurysmal anatomy with three-dimensional time-of-flight (3D-TOF) MR angiography before and after treatment with Guglielmi detachable coils (GDCs) and with CT angiography before and after treatment with stents and stent-grafts. We investigated the ability of time-resolved contrast-enhanced 3D MR angiography (3D MR digital subtraction angiography [DSA]) to accurately depict the anatomy of experimental lateral aneurysms before and after treatment with GDCs and a variety of stents or stent-grafts, and compared these findings with 3D-TOF MR angiography without and with contrast enhancement and CT angiography. METHODS: Two nitinol stents, two nitinol-polytetrafluoroethylene (PTFE) stent-grafts, and two stainless steel stents were deployed in three dogs with experimental carotid aneurysms. In a fourth animal, one of three aneurysms was completely occluded with GDCs. The other two aneurysms were loosely packed to ensure persistence of some residual aneurysmal lumen. Cut-film angiography, CT angiography, 3D-TOF MR angiography without and with contrast enhancement, and 3D MR DSA were performed in all dogs before and 3 weeks after treatment. RESULTS: 3D MR DSA was superior to conventional 3D-TOF MR angiography without and with contrast enhancement in accurately depicting experimental lateral aneurysms and superior to CT angiography in depicting aneurysms treated by GDCs. 3D MR DSA and CT angiography were comparable in depicting vessels treated with nitinol stents and stent-grafts, whereas CT angiography was superior for showing vessels treated by stainless steel stents. CONCLUSION: We recommend further development and clinical evaluation of 3D MR DSA for imaging cerebral aneurysms before and after treatment with GDCs. 3D MR DSA or CT angiography may be useful for evaluating vessels containing nitinol stents or nitinol-PTFE stent-grafts, whereas CT angiography should be used for follow-up of vessels treated by stainless steel stents.
BACKGROUND AND PURPOSE: Vascular abnormalities, such as atherosclerosis and the growth and rupture of cerebral aneurysms, result from a derangement in tissue metabolism and injury that are, in part, regulated by hemodynamic stress. The purpose of this study was to establish the feasibility and accuracy of determining wall shear rate in the internal carotid artery from phase-contrast MR data. METHODS: Three algorithms were used to generate shear rate estimates from both ungated and cardiac-gated 2D phase-contrast data. These algorithms were linear extrapolation (LE), linear estimation with correction for wall position (LE*), and quadratic extrapolation (QE). In vitro experiments were conducted by using a phantom under conditions of both nonpulsatile and pulsatile flow. The findings from five healthy volunteers were also studied. MR imaging-derived shear rates were compared with values calculated by solving the fluid flow equations. RESULTS: Findings of in vitro constant-flow experiments indicated that at one or two excitations, QE has the advantage of good accuracy and low variance. Results of in vitro pulsatile flow experiments showed that neither LE* nor QE differed significantly from the predicted value of wall shear stress, despite errors of 17% and 22%, respectively. In vivo data showed that QE did not differ significantly from the predicted value, whereas LE and LE* did. The percentages of errors for QE, LE, and LE* in vivo measurements were 98.5%, 28.5%, and 36.1%, respectively. The average residual of QE was low because the residuals were both above and below baseline whereas, on average, LE* tended to be a more biased overestimator of the shear rate in volunteers. The average and peak wall shear force in five volunteers was approximately 8.10 dyne/cm2 and 13.2 dyne/cm2, respectively. CONCLUSION: Our findings show that LE consistently underestimates the shear rate. Although LE* and QE may be used to estimate shear rate, errors of up to 36% should be expected because of variance above and below the true value for individual measurements.
BACKGROUND AND PURPOSE: The major factor influencing the effectiveness of Guglielmi detachable coils (GDCs) in the treatment of saccular aneurysms is the size of the aneurysm's ostium (neck). Current imaging techniques often do not allow accurate assessment of aneurysm neck morphology. The primary purpose of this study was to determine the feasibility of using intravascular sonography to provide this information. METHODS: Lateral and bifurcation aneurysms were created in each of six adult mongrel dogs by using a well-established surgical technique. Aneurysms were evaluated with digital subtraction angiography and intravascular sonography before (n = 12) and after (n = 6) treatment with GDCs. Angiography was performed using standard techniques. Sonography was performed using both a commercially available 2.6F 40-MHz catheter and a preproduction 0.014-inch 40-MHz imaging core wire housed in a Tracker catheter. Angiograms and sonograms were reviewed independently by two observers to assess the clarity and accuracy with which they depicted the size of each aneurysm's ostium. Posttreatment intravascular sonograms were evaluated for the extent to which they depicted the completeness of aneurysm obliteration. Two-dimensional reformatted images were made of the intravascular sonographic pullback sequences. RESULTS: In all instances, intravascular sonography provided clear definition of the aneurysm's neck (ostium) morphology as well as its relationship to the parent artery and adjacent branches, especially when 2D reformatted images were obtained. The position of coils in aneurysms was also clearly defined. CONCLUSION: Intravascular sonography is a novel technique for viewing the ostium (neck) of an aneurysm. It provides information not available with current angiographic methods.
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A new, fast, 2D MR imaging technique allowing passive catheter visualization adequate for use as a tool for guiding the movement of a catheter during endovascular procedures is described. This imaging technique samples low spatial frequencies more often than high spatial frequencies; it also uses both k-space view sharing and temporal interpolation. Unlike other techniques for passive visualization that exploit magnetic-susceptibility-induced artifacts, we have adopted a strategy that takes advantage of the T1-shortening effect of paramagnetic contrast agents, such as Gd-DTPA and a projection dephaser. This not only permits visualization of the entire catheter length but also minimizes the risk of intravascular heating. Using this method, a temporal frame rate of up to eight images per second and a tip localization accuracy of +/- 1mm (root mean square difference) can be achieved.
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