BACKGROUND: Current intravascular ultrasound (IVUS) catheters provide transverse imaging at the level of the ultrasound transducer. This limits imaging to large-diameter segments without critical atherosclerotic narrowings. We have developed a prototype 20-MHz forward-viewing IVUS catheter that provides two-dimensional sector imaging distal to the catheter tip. A present limitation of this technique is that the catheter must be manually rotated to obtain multiple longitudinal views required to integrate the segment into a three-dimensional matrix. To overcome this, we have developed an algorithm that reconstructs these multiple two-dimensional forward-viewing IVUS images into a three-dimensional matrix for more complete depiction of the segment distal to the ultrasound catheter. This algorithm allows display and multidimensional slicing of the three-dimensional reconstruction. METHODS AND RESULTS. To test our algorithms, five arterial segments (three canine aortas, two human femoral arteries) were evaluated in vitro. In each segment, 36 forward-viewing longitudinal slices were collected, digitized, processed, and reoriented to produce a three-dimensional reconstruction (3DR) matrix. The matrix data were sliced into parallel transverse sections and compared with morphometric interpretation of histological sections (Histo). As a result, image data could be reconstructed for a distance of 2.0 cm ahead of the catheter. 3DR easily demonstrated wall and luminal morphology and provided transverse IVUS images comparable to the histological specimens. A good correlation was noted between Histo- and 3DR-determined luminal diameters (LD) and luminal areas: 3DR LD = 1.4 Histo LD-0.4, r = .86; 3DR LD = 0.7 +/- 0.20 cm (mean +/- SD); and Histo LD = 0.7 +/- 0.13 cm. CONCLUSIONS: These preliminary data demonstrate the feasibility of 3DR of forward-viewing IVUS data. This method allows rapid, detailed analysis of diseased arterial segments previously unavailable with standard IVUS and may permit better targeting of interventional techniques.
A method employing intravascular ultrasound (IVUS) and simultaneous hemodynamic measurements, with resultant finite element analysis (FEA) of accurate three-dimensional IVUS reconstructions (3-DR), was developed to estimate the regional distribution of arterial elasticity. Human peripheral arterial specimens (iliac and femoral, n = 7) were collected postmortem and perfused at three static transmural pressures: 80, 120, and 160 mmHg. At each pressure, IVUS data were collected at 2.0-mm increments through a 20.0-mm segment and used to create an accurate 3-DR. Mechanical properties were determined over normotensive and hypertensive ranges. An FEA and optimization procedure was implemented in which the elemental elastic modulus was scaled to minimize the displacement error between the computer-predicted and actual deformations. The “optimized” elastic modulus (Eopt) represents an estimate of the component element material stiffness. A dimensionless variable (beta), quantifying structural stiffness, was computed. Eopt of nodiseased tissue regions (n = 80) was greater than atherosclerotic regions (n = 88) for both normotensive (Norm) and hypertensive (Hyp) pressurization: Norm, 9.3 +/- 0.98 vs. 3.5 +/- 0.30; Hyp, 11.3 +/- 0.72 vs. 8.5 +/- 0.47, respectively (mean +/- SE x 10(6) dyn/cm2; P < 0.01 vs. nondiseased). No differences in beta between nondiseased and atherosclerotic tissue were noted at Norm pressurization. With Hyp pressurization, beta of atherosclerotic regions were greater than nondiseased regions: 21.5 +/- 2.21 vs. 14.0 +/- 2.11, respectively (P < 0.03). This method provides a means to identify regional in vivo variations in mechanical properties of arterial tissue.
Three-dimensional reconstructions (3DR) of the heart and great vessels are conventionally formed by scanning a single two-dimensional (2-D) plane, and then combining the data in this scan with data obtained from other scan planes taken at different levels. Missing data between planes are filled in by interpolation. Applications of such 3DR's from ultrasonic, radionuclide and magnetic resonance images have yielded promising results (1). 3DR's of the left ventricle have been obtained from cardiac ultrasonic and ultrafast computed tomographic images in our laboratory (2,3). We have also utilized the reconstructed geometries for analysis of mechanical deformation of the ventricular chamber and quantitative assessment of wall motion abnormalities in diseased states (4).
The aim of this study was to determine whether gadofluorine, a paramagnetic magnetic resonance imaging (MRI) contrast agent, selectively enhances carotid atherosclerotic plaques in Yucatan miniswine.Atherosclerotic plaques were induced in the left carotid arteries (LCA) of Yucatan miniswine (n=3) by balloon denudation and high cholesterol diet. T1-weighted MRI was performed before and 24 hours after gadofluorine injection (at a dose of 100 micromol/kg) to assess the enhancement of the balloon-injured LCA wall relative to healthy, uninjured right carotid artery (RCA) wall. Histopathology was performed to verify the presence and composition of the atherosclerotic plaques imaged with MRI.Gadofluorine was found to enhance LCA atherosclerotic lesions relative to RCA wall by 21% (P<0.025) 24 hours after contrast injection. Enhancement of healthy LCA wall relative to healthy RCA wall was not observed.Gadofluorine selectively enhances carotid atherosclerotic plaques in Yucatan miniswine. Gadofluorine appears to be a promising MR contrast agent for detection of atherosclerotic plaques in vivo.
Introduction: Pulmonary artery systolic pressure (PASP) can be derived from maximum tricuspid regurgitation velocity (TRV) obtained from echo using a modified Bernoulli equation. However, PASP from an unenhanced echo only modestly correlates to invasively measured PASP. This study evaluates whether the accuracy of PASP from an echo can be improved by using contrast agents. Methods: Ninety consecutive patients undergoing clinically indicated right heart catheterization were recruited to perform simultaneous echo. TRV was measured in an echo unenhanced (UE), with agitated saline (AgS), and with echo contrast (EC) (routinely injected centrally, and peripherally in 21 patients). PASP was then calculated using the formula PASP=4(TRV 2 )+RAP, where RAP was estimated on echo by inferior vena cava collapsibility. Data was analyzed using paired t-test and linear regression (JMP Pro13). Results: Average age was 54 (±13) years with 58% males, 73% heart transplant recipients, and 38% with pulmonary hypertension. UE PASP was significantly lower than RHC PASP with a mean difference of -6.09 mm Hg (p<0.001) and correlation coefficient of 0.57 (p<0.001). In comparison, AgS PASP had a smaller mean difference of 0.41 mm Hg (p=0.641) and a higher correlation coefficient of 0.73 (p<0.001). EC-enhanced echo also yielded a smaller mean difference (central: -1.82 mm Hg with p=0.049; peripheral: -3.21 mm Hg with p=0.095) and an even higher correlation coefficient (central: r=0.74; peripheral: r=0.81). Number of patients with accurate PASP from echo (defined as PASP difference <10 mm Hg between echo and RHC) was improved from 65% (UE) to 77% (AgS), 82% (EC-central), and 71% (EC-peripheral). Conclusion: Echo with agitated saline yielded the closest mean PASP compared to invasivePASP, whereas echo with peripherally administered EC yielded the highest correlation coefficient. Echo enhancement with either Ags or EC can improve the accuracy of the estimated PASP compared to UE studies.
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