Evaluation of endovenous radiofrequency ablation and laser therapy with endoluminal optical coherence tomography in an ex vivo model.

BACKGROUND: This study evaluated the ability of endovascular optical coherence tomography (eOCT) to detect qualitative tissue alteration and quantitative changes of vein wall thickness and vein lumen diameter comparing endovenous radiofrequency ablation (RFA) and endovenous laser therapy (ELT) in an established ex vivo model. METHODS: Endoluminal eOCT was performed by means of a new prototype rotating system (System M1, LightLab Imaging Inc, Boston, Mass) with automatic pullback of 1 mm/s. In the course of an eOCT examination of a 50-mm vein segment, 264 electronic cross section images with a spatial resolution of 15 to 20 mum are acquired. The eOCT scans were performed before and after treatment of each of 13 treated vein segments and of six control vein segments. Thirteen subcutaneous cow foot veins were reperfused in situ, and the defined 50-mm vein segments in the study were treated with RFA (n = 2) and ELT (n = 11). RFA followed the clinical VNUS-Closure protocol (VNUS Medical Technologies, San Jose, Calif) using a 6F 60-mm Closure-Plus catheter. ELT was performed using light of lambda = 980 nm with a laser power of 3 (n = 2), 5 (n = 2), and 7 W (n = 4) with a paced pullback protocol with laser irradiation for 1.5 seconds every 3 mm, resulting in linear endovenous energy densities (LEED) of 15, 25, and 35 J/cm. Using 11 W (n = 3) with a continuous pullback protocol at 3 mm/s resulted in a LEED of 36.5 J/cm. Ten histologic cross sections of each treated and control vein segment were correlated with the corresponding eOCT cross sections to evaluate qualitative representation of vein wall layers and tissue alterations such as ablation and vein wall perforation. In addition, 26 eOCT cross sections of every treated vein segment before and after treatment and every control vein segment were analyzed to calculate quantitative changes in media thickness and vein lumen diameter. RESULTS: In all specimens, qualitative analysis with eOCT demonstrated a clear match with histologic cross sections. A symmetrical, complete, circular disintegration of intima and media structures, without any transmural tissue defects, was shown after RFA. Pronounced semicircular tissue ablations (3 to 14 per 50 mm) and complete vessel wall perforations (0 to 16 per 50 mm) were detected after ELT. The quantitative analysis demonstrated a significant (P < .0001) increase in intima-media thickness after RFA (37.8% to 66.7%) and ELT (11.1% to 45.7%). A significant (P < .0001) reduction of vessel lumen diameter (36.3% to 42.2%) was found after RFA. Owing to the limited number of treated vein segments and inhomogeneous baseline vein lumen diameters, no linear correlation between laser energy level and effects on tissue such as ablation/perforation, media thickening, or vein lumen diameter could be identified. CONCLUSIONS: In our ex vivo cow foot model, eOCT is able to reproduce normal vein wall structures and endovenous acute thermal alterations, such as tissue ablation and vessel wall perforations. Endovenous eOCT images can also be analyzed quantitatively to measure media thickness or vein lumen diameter. Endovascular OCT could become a valuable alternative tool for morphologic investigation of tissue alterations after endovenous thermal procedures.

Endovascular optical coherence tomography ex vivo: venous wall anatomy and tissue alterations after endovenous therapy.

Endovascular optical coherence tomography (OCT) is a new imaging modality providing histology-like information of the venous wall. Radiofrequency ablation (RFA) and laser therapy (ELT) are accepted alternatives to surgery. This study evaluated OCT for qualitative assessment of venous wall anatomy and tissue alterations after RFA and ELT in bovine venous specimens. One hundred and thirty-four venous segments were obtained from ten ex-vivo bovine hind limbs. OCT signal characteristics for different wall layers were assessed in 180/216 (83%) quadrants from 54 normal venous cross-sections. Kappa statistics (kappa) were used to calculate intra- and inter-observer agreement. Qualitative changes after RFA (VNUS-Closure) and ELT (diode laser 980 nm, energy densities 15 Joules (J)/cm, 25 J/cm, 35 J/cm) were described in 80 venous cross-sections. Normal veins were characterized by a three-layered appearance. After RFA, loss of three-layered appearance and wall thickening at OCT corresponded with circular destruction of tissue structures at histology. Wall defects after ELT ranged from non-transmural punctiform damage to complete perforation, depending on the energy density applied. Intra- and inter-observer agreement for reading OCT images was very high (0.90 and 0.88, respectively). OCT allows for reproducible evaluation of normal venous wall and alterations after endovenous therapy. OCT could prove to be valuable for optimizing endovenous therapy in vivo.

Catheter-based intraluminal optical coherence tomography (OCT) of the ureter: ex-vivo correlation with histology in porcine specimens.

Intraluminal optical coherence tomography (OCT) applies coherent light to provide cross-sectional images with a spatial resolution of 10-25 microm. We compared OCT and matching whole-mount histology microscopy sections of porcine upper ureters ex vivo for visualization and delineation of different tissue layers of the ureteral wall. Porcine ureters (six specimens, 24 quadrants) were flushed with normal saline solution prior to insertion of the OCT catheter (diameter, 0.014 inch, OCT wavelength, 1,300+/-20 nm). Cross-sectional OCT images were obtained in marked locations before specimens were fixed in 4% formalin, cut at marked locations, whole-mounted, and stained with hematoxilin and eosin. Visualization and delineation of different tissue layers of the ureteral wall by OCT was compared with matching histology by two independent observers (O1,O2). OCT distinguished tissue layers of the ureteral wall in all quadrants. In OCT images, O1/O2 delineated urothelium and lamina propria in 23/24 quadrants, lamina propria and muscle layer in 19/16 quadrants, inner and outer muscle layer in 13/0 quadrants, and urothelial cell layers in 13/2 quadrants, respectively. Intraluminal OCT provides histology-like images of the ureter in porcine specimens ex vivo and reliably distinguishes between urothelium and deeper tissue layers of the ureteral wall.

Intravascular optical coherence tomography: comparison with histopathology in atherosclerotic peripheral artery specimens.

PURPOSE: Intravascular optical coherence tomography (OCT) is a new imaging modality that provides microstructural information on atherosclerotic plaques and has an axial resolution of 10-20 microm. OCT of coronary arteries characterizes different atherosclerotic plaque components by their distinctive signal patterns. Peripheral human arteries were examined ex vivo by means of OCT, and attempts to distinguish among fibrous, lipid-rich, and calcified atherosclerotic plaques were made based on imaging criteria previously established for coronary arteries. MATERIALS AND METHODS: One hundred fifty-one atherosclerotic arterial segments were obtained from 15 below-knee amputations. OCT imaging criteria for different plaque types (fibrous, lipid-rich, calcified) were established in a subset of 30 arterial segments. The remaining 121 OCT images were analyzed by two independent readers. Each segment was divided into four quadrants. Agreement between histopathology and OCT was quantified by the kappa test of concordance, as were interobserver, intraobserver, and inter-method variability. RESULTS: Four hundred sixty-nine of 484 quadrants (97%) were available for comparison. Sensitivity and specificity for OCT criteria (consensus readers 1 and 2) were 86% and 86% for fibrous plaques, 78% and 93% for lipid-rich plaques, and 84% and 95% for calcified plaques, respectively (overall agreement, 84%). The interobserver and intraobserver reliabilities of OCT assessment were high (kappa values of 0.84 and 0.87, respectively). The inter-method agreement was 0.74 for consensus OCT versus consensus histology. CONCLUSIONS: OCT of peripheral human arteries ex vivo characterized different atherosclerotic plaque types with a high degree of agreement with histopathologic findings. Findings were comparable to those reported for coronary arteries. OCT promises to improve understanding of the progression or regression of peripheral atherosclerosis in vivo.

Critical limb ischemia: hybrid MR angiography compared with DSA.

PURPOSE: To compare a hybrid magnetic resonance (MR) angiography protocol with selective digital subtraction angiography (DSA) in patients with critical limb ischemia. MATERIALS AND METHODS: The study was approved by the institutional review board, and written consent was obtained from all patients. Pretreatment DSA and hybrid MR angiography were performed in 19 consecutive patients (15 men, four women; mean age, 69.8 years; range, 44-86 years). Hybrid MR angiography included submillimeter dual-phase three-dimensional gadolinium-enhanced MR angiography in lower calf and foot, and four-station bolus-chase MR angiography in pelvis, thigh, and upper calf. Three readers identified the target lesion and inflow and outflow segments and determined treatment (bypass graft placement, percutaneous transluminal angioplasty, conservative management, amputation). Results of interobserver and intermethod comparisons were expressed as percentage of agreement and 95% confidence interval (CI). RESULTS: On hybrid MR angiograms, no substantial venous overlay was present and image quality was excellent or adequate in 18 (95%) of 19 limbs. Readers 1, 2, and 3 selected the identical target lesion on the DSA image and the MR angiogram in 18, 17, and 18 of 18 comparable limbs, respectively. Mean percentage of agreement for readers 1 and 3 was 100% (95% CI: 81%, 100%) and for reader 2 was 94% (95% CI: 73%, 100%). Agreement of all three readers was superior with use of MR angiography for determination of inflow segments (13 [72%] of 18 limbs) and outflow segments (17 [94%] of 18 limbs), compared with agreement with use of DSA (13 [68%] of 19 inflow segments, 10 [53%] of 19 outflow segments). Agreement in therapy decisions was higher with DSA (15 [79%] of 19) than with MR angiography (11 [61%] of 18). CONCLUSION: Preliminary data strongly support the combination of submillimeter dual-phase MR angiography in lower calf and foot with four-station bolus-chase MR angiography to extend the utility of MR angiography to patients with critical limb ischemia.

Magnetic resonance angiography in the follow-up of distal lower-extremity bypass surgery: comparison with duplex ultrasound and digital subtraction angiography.

PURPOSE: The danger of limb loss as a consequence of acute occlusion of infrapopliteal bypasses underscores the requirement for careful patient follow-up. The objective of this study was to determine the agreement and accuracy of contrast material-enhanced moving-table magnetic resonance (MR) angiography and duplex ultrasonography (US) in the assessment of failing bypass grafts. In cases of discrepancy, digital subtraction angiography (DSA) served as the reference standard. MATERIALS AND METHODS: MR angiography was performed in 24 consecutive patients with 26 femorotibial or femoropedal bypass grafts. Each revascularized limb was divided into five segments--(i) native arteries proximal to the graft; (ii) proximal anastomosis; (iii) graft course; (iv) distal anastomosis; and (v) native arteries distal to the graft-resulting in 130 vascular segments. Three readers evaluated all MR angiograms for image quality and the presence of failing grafts. The degree of stenosis was compared to the findings of duplex US, and in case of discrepancy, to DSA findings. Two separate analyses were performed with use of DSA only and a combined diagnostic endpoint as the reference standard. RESULTS: Image quality was rated excellent or intermediate in 119 of 130 vascular segments (92%). Venous overlay was encountered in 26 of 130 segments (20%). In only two segments was evaluation of the outflow region not feasible. One hundred seventeen of 130 vascular segments were available for quantitative analysis. In 109 of 117 segments (93%), MR angiography and duplex US showed concordant findings. In the eight discordant segments in seven patients, duplex US overlooked four high-grade stenoses that were correctly identified by MR angiography and confirmed by DSA. Percutaneous transluminal angioplasty was performed in these cases. In no case did MR angiography miss an area of stenosis of sufficient severity to require treatment. Total accuracy for duplex US ranged from 0.90 to 0.97 depending on the reference standard used, whereas MR angiography was completely accurate (1.00) regardless of the standard definition. CONCLUSION: Our data strongly suggest that the accuracy of MR angiography for identifying failing grafts in the infrapopliteal circulation is equal to that of duplex US and superior to that of duplex US in cases of complex revascularization. MR angiography should be included in routine follow-up of patients undergoing infrapopliteal bypass surgery.

High-resolution MR imaging of human atherosclerotic femoral arteries in vivo: validation with intravascular ultrasound.

PURPOSE: To establish a magnetic resonance (MR) imaging protocol for noninvasive in-vivo analysis of atherosclerotic femoral artery segments in humans and to compare the results to those of intravascular ultrasonography (IVUS). MATERIALS AND METHODS: In seven patients with peripheral arterial occlusive disease, 20 femoral arterial segments per person were examined by high-resolution (HR) MR imaging and IVUS. Comparison was possible in 123 of 140 segments. MR imaging was performed at 1.5 T with use of a three-dimensional (3D) time-of-flight sequence with an in-plane resolution of 0.78 x 0.49 mm(2). 3D contrast-enhanced MR angiography was used for exact positioning of the HR MR imaging slices. IVUS (3.5 F, 40 MHz) was performed with use of a motorized pullback system. Parameters analyzed included cross-sectional lumen area (LA), vessel area (VA), and extent of vessel wall calcification. RESULTS: Agreement between IVUS and HR MR imaging was analyzed with use of the Bland-Altman method. The paired LA measurements were in close agreement: the Bland-Altman mean bias in LA was -0.4 mm with a precision of +/-5.1 mm (P =.062). As a result of dorsal echo extinction in IVUS, VA measurements were feasible in only 74 of 140 segments. VA measurements were moderately correlated (r = 0.74; P <.0001), and a 25% overestimation by HR MR imaging compared to IVUS was observed. Intra- and interobserver comparisons for LA and VA measured with HR MR imaging did not show significant differences. Vessel wall calcifications were classified with a sensitivity of 91%, a specificity of 93%, and an accuracy of 93%. CONCLUSIONS: The MR imaging protocol introduced in the present study permits precise assessment of LA and extent of calcification in peripheral arterial occlusive disease in vivo. HR MR imaging shows high concordance with IVUS and may have the potential for noninvasive therapy monitoring.