Improved method for spectral reflectance estimation and application to mobile phone cameras.

We propose an improved method for estimating surface-spectral reflectance from the image data acquired by an RGB digital camera. We suppose a multispectral image acquisition system in the visible range, where a camera captures multiple images for the scene of an object under multiple light sources. First, the observed image data are described using the camera spectral sensitivities, the surface-spectral reflectance, the illuminant spectral power distributions, an additive noise term, and a gain parameter. Then, the optimal reflectance estimate is determined to minimize the mean-square error between the estimate and the original surface-spectral reflectance. We attempt to further improve the estimation accuracy and develop a novel linear estimator in a more general form than the Wiener estimator. Furthermore, we calibrate the imaging system using a reference standard sample. Finally, experiments are performed to validate the proposed method for estimating the surface-spectral reflectance using different mobile phone cameras.

Measurement and Estimation of Spectral Sensitivity Functions for Mobile Phone Cameras.

Mobile phone cameras are often significantly more useful than professional digital single-lens reflex (DSLR) cameras. Knowledge of the camera spectral sensitivity function is important in many fields that make use of images. In this study, methods for measuring and estimating spectral sensitivity functions for mobile phone cameras are developed. In the direct measurement method, the spectral sensitivity at each wavelength is measured using monochromatic light. Although accurate, this method is time-consuming and expensive. The indirect estimation method is based on color samples, in which the spectral sensitivities are estimated from the input data of color samples and the corresponding output RGB values from the camera. We first present an imaging system for direct measurements. A variety of mobile phone cameras are measured using the system to create a database of spectral sensitivity functions. The features of the measured spectral sensitivity functions are then studied using principal component analysis (PCA) and the statistical features of the spectral functions extracted. We next describe a normal method to estimate the spectral sensitivity functions using color samples and point out some drawbacks of the method. A method to solve the estimation problem using the spectral features of the sensitivity functions in addition to the color samples is then proposed. The estimation is stable even when only a small number of spectral features are selected. Finally, the results of the experiments to confirm the feasibility of the proposed method are presented. We establish that our method is excellent in terms of both the data volume of color samples required and the estimation accuracy of the spectral sensitivity functions.

Occlusion of canine aneurysms using microporous self-expanding stent grafts: long-term follow-up.

PURPOSE: The treatment of large or giant cerebral aneurysms by surgical and/or endovascular techniques is difficult and poses relatively high risks. Therefore, a microporous self-expanding (hybrid) stent graft composed of a thin, expandable, segmented polyurethane (SPU) membrane with micropores and a drug-delivery system was developed. MATERIALS AND METHODS: A commercially available, self-expanding carotid stent was covered with a thin microporous SPU membrane fabricated by the dip-coating method and the excimer laser ablation technique, with an intraluminal coating of argatroban. Experimentally fabricated lateral-wall aneurysms in canine carotid arteries using venous pouches were occluded with the hybrid stent graft (bale-shaped pore density of 23.6%) on one side and a bare-metal stent on the other side without systemic antiplatelet therapy. RESULTS: Angiography at 1, 6, and 12 months of stenting revealed that all arteries were patent without marked stenosis without systemic antiplatelet therapy. All aneurysms treated with hybrid stent grafts remained occluded throughout the 12-month period, while among those treated by bare-metal stents, 2 of 3 aneurysms were occluded at 6 months (67%) and only 1 of 3 aneurysms were occluded at 12 months (33%). Histology revealed that the novel hybrid stent graft had less intimal hyperplasia than the bare-metal stent. The hybrid stent graft was useful for the successful occlusion of these canine carotid aneurysms, even at 12 months. CONCLUSIONS: The novel hybrid stent grafts are expected to overcome the disadvantages of fully covered stent grafts and simple bare-metal stents, while combining both their merits, and appear to be useful in the treatment of large or giant cerebral aneurysms.

Treatment of rabbit carotid aneurysms by hybrid stents (microporous thin polyurethane-covered stents): preservation of side-branches.

OBJECTIVE: We sought to determine the patency of normal arterial branches from the covered segments of an artery after stenting. BACKGROUND: Most intracranial aneurysms occur at arterial branching points (bifurcations, side-branches, or perforators). The post-stenting patency of normal arterial branches from the covered segments of the artery is important. We have previously developed a hybrid stent with micropores to prevent early parent artery occlusion by more early endothelialization, and mid- to long-term parent artery stenosis by control of intimal hyperplasia after aneurysm occlusion. METHODS: We created aneurysms in 10 rabbits by distal ligation and intraluminal incubation of elastase within an endovascularly trapped proximal segment of the common carotid artery. All animals were treated with hybrid stents having micropores. Four animals were observed for one month and three each for three and 12 months. The patency of the side-branches of the subclavian artery was evaluated angiographically and in some cases, histologically. RESULTS: Aneurysms were completely occluded at all time points other than 12 months. The subclavian artery and brachiocephalic artery were patent, without significant stenosis. All the side-branches of the subclavian artery detected on the preoperative angiogram remained patent at the final assessment. CONCLUSION: The use of hybrid stents for aneurysm repair and side-branch patency seems to be effective, as per the long-term results obtained in an animal model.

Development of microporous self-expanding stent grafts for treating cerebral aneurysms: designing micropores to control intimal hyperplasia.

Treatment of large (diameter 12-25 mm) or giant (diameter >25 mm) cerebral aneurysms with a broad neck in the cranio-cervical area is difficult and carries relatively high risks, even with surgical and/or endovascular methods. To this end, we have been developing a high-performance, self-expanding stent graft which consists of a commercially available NiTi stent (diameter 5 mm, length 20 mm) initially covered with a thin microporous segmented polyurethane membrane fabricated by the dip-coating method. Micropores are then created by the excimer laser ablation technique, and the outer surface is coated with argatroban. There are 2 types of micropore patterns: circular-shaped pore type (pore: diameter 100 µm, opening ratio 12.6%) and the bale-shaped pore type (pore: size 100 × 268 µm, opening ratio 23.6%). This self-expanding stent graft was tested on side-wall aneurysms of both canine carotid arteries that were experimentally induced using the venous pouches from the external jugular veins, with the self-expanding stent graft on one side and a bare self-expanding stent on the other side. All carotid arteries were patent and free of marked stenosis after 1 month. All aneurysms were occluded by stent grafts, while patent in those treated with bare stents. Histologically, the stent grafts with bale-shaped micropores and a high opening ratio were associated with less intimal hyperplasia (187 ± 98 µm) than the bare stents (341 ± 146 µm) or the stent grafts with circular micropores and a low opening ratio (441 ± 129 µm). A pore ratio of 23.6% was found to control intimal growth.

High-performance self-expanding stent graft: development and application to experimental aneurysms.

Large or giant aneurysms in the craniocervical area with broad necks are of concern and are treated surgically, endovascularly, or in both ways. Surgically, their treatment is difficult, with relatively high risks. For their embolization, we have been developing a high-performance stent graft that has three characteristics: a thin and expandable segmented polyurethane (SPU) membrane, micropores formed by the excimer laser ablation technique, and a drug delivery system at the membrane. Stent grafts were fabricated using commercially available self-expanding stents. These stents were covered with a thin SPU membrane by the dip-coating method. Micropores were then formed by the excimer laser ablation technique and an argatroban coating was added. We tested the effectiveness of this new stent graft by treating experimental canine aneurysms. Experimental aneurysms were made in the bilateral carotid arteries of four female beagles by end-to-side anastomosis using an autologous venous pouch. One month after aneurysm formation, the experimental aneurysm in one of the carotid arteries was covered with our self-expanding stent graft and the aneurysm in the other artery was covered with a bare self-expanding stent. On angiograms 1 month after stenting, the aneurysms treated with our stent graft were completely occluded without significant parent artery stenosis, but the aneurysms treated with the original bare stent were still open. Our high-performance self-expanding stent graft was easily applied to the experimental aneurysms and accomplished complete occlusion of aneurysms in beagles. Further study should be performed for the goal of clinical use.

Development of novel covered stents using salmon collagen.

In this study, we newly developed self-expandable or balloon-expandable covered stents with a biodegradable salmon collagen (SC) film. The SC-covered stents were fabricated by placing a bare stent in a mixture of acidic SC solution and a fibrillogenesis-inducing buffer (pH 6.8) including a cross-linking agent (water-soluble carbodiimide), and subsequent incubation at 4 degrees C for 24 h and lyophilization. The stents obtained were completely covered with an SC film having a nanofibrous structure (fibril diameter, about 70 nm). On immersion in water, the film is converted to a gel with slight swelling. There was no rupture of the SC cover after mounting on a balloon catheter or after expansion. Preliminary implantation was conducted by placing the balloon-expandable covered stents in the common carotid arteries of beagles. One month after implantation, angiography showed that all stented arteries were patent with no significant neointimal thickening. In conclusion, SC is potentially useful as a cover material of endovascular stents to enhance patency.

A "mouse in a trap" method for cerebral protection during carotid stenting: Technical note.

Carotid artery angioplasty and stenting (CAS) is now used as an alternative to surgical endarterectomy. The introduction of cerebral protection systems during stenting has improved carotid artery stenosis treatment, with less periprocedural complications. A "mouse in a trap" method was conceived and used in three patients. This involved an emboli entrapment-aspiration system using one proximal occluder in the common carotid artery and two distal occluders in the internal carotid artery or external carotid artery, followed by serial inflation-deflation cycles during each carotid stenting procedure. Debris was retrieved before dilation in one patient, after deployment in one, and after dilation in two. Although only used in a few cases to date, the method may improve the practice of CAS in treating patients with carotid stenosis, resulting in less thromboembolic events.

Stent-supported coil embolization for carotid artery pseudoaneurysm as a complication of endovascular surgery--case report.

A 57-year-old male presented with right amaurosis fugax and left transient ischemic attack caused by stenosis of the intracranial segment of the right internal carotid artery (ICA). Percutaneous transluminal angioplasty with stenting was successfully performed to dilate the stenosis. However, serial angiography revealed the development of a large pseudoaneurysm in the cervical ICA, probably as a result of carotid wall injury caused by the guiding catheter during the procedures. The patient underwent a second endovascular angioplasty. A Palmaz stent was placed across the aneurysm neck to stabilize the carotid wall. Guglielmi detachable coils were then inserted into the aneurysm cavity through the stent struts to successfully obliterate the aneurysm. Both the angiographical results and the patient's outcome were favorable. Stent-supported coil embolization is an effective and safe technique for medically refractory pseudoaneurysms, and may be a useful alternative to direct surgery.

Occlusion of experimental aneurysms with heparin-loaded, microporous stent grafts.

OBJECTIVE: An embolization technique using a stent graft has been developed to replace the conventional type of direct surgery or neurointervention with platinum coils and/or bare stents. The utility of a commercially available metal stent wrapped with a microporous elastomeric film coated with a thin, heparin-loaded, photocured gelatinous layer for the treatment of experimental carotid artery sidewall aneurysms in dogs was evaluated. METHODS: The stent graft was used for embolization of experimental carotid artery aneurysms in dogs. The aneurysms were prepared bilaterally in canine carotid arteries with branching of an external jugular vein patch. RESULTS: The entries into all of the aneurysms were occluded immediately after placement of the stent grafts, and the aneurysms were embolized by thrombus formation even 1 week after deployment. All of the parent carotid arteries in which stent grafts were placed were patent, without severe stenosis, immediately (n = 2), 1 week (n = 4), 1 month (n = 3), and 3 months (n = 4) after placement. Scanning electron microscopy demonstrated that the luminal surfaces of the stent grafts were entirely endothelialized as soon as 1 week after placement, via transmural tissue ingrowth through the micropores formed in the covering film. CONCLUSION: The stent graft we have developed seems to be highly promising for the treatment of aneurysms, especially with respect to immediate termination of blood inflow for aneurysm occlusion and rapid endothelialization in the aneurysm neck.

Fabrication of drug-eluting covered stents with micropores and differential coating of heparin and FK506.

To reduce in-stent restenosis rates, we developed a novel drug-eluting covered stent with a microporous elastometric covered film, in which its luminal surface was flat and immobilized with heparin for anticoagulation and its outer surface immobilized with FK506 to prevent neointimal hyperplasia. One month after implantation into the bilateral common carotid arteries, all stented arteries were patent and the luminal surfaces were fully covered with a confluent of endothelial cells irrespective of the drug immobilization. In the control group, which consisted of covered stents without drug immobilization, intensive inflammatory cells adjacent to the stents and neointimal hyperplasia, indicating vascular injury, were observed. In contrast, in the developed drug-eluting stents, only a few inflammatory cells around the stent strut and covered film were observed, and there was no significant neointimal thickening.

Embolization of experimental aneurysms using a heparin-loaded stent graft with micropores.

PURPOSE: For percutaneous transluminal angioplasty (PTA), a heparin-loaded stent graft, composed of a commercially available metallic stent with a microporous and surface-modified thin film, has been developed. Early controlled endothelialization is promoted by a regular array of micropores produced by an excimer laser ablation technique. Early thrombus is prevented by a drug delivery system established by impregnation of photoreactive gelatin with heparin. Our stent grafts were used for embolization of experimental carotid aneurysms with an autologous external jugular vein patch in dogs. MATERIALS AND METHODS: At 1 month after formation, the aneurysms were occluded with stent grafts. Affected arteries were removed with the aneurysms, immediately (two aneurysms in one dog), 1 week (four aneurysms in two dogs), 1 month (three aneurysms in two dogs) and 3 months (four aneurysms in two dogs) after embolization, and were studied histologically to evaluate patency and endothelialization over the intraluminal surface of the thin film. RESULTS: Treated carotid arteries were all patent with occluded aneurysms completely at any periods. Even at 1 week after embolization, endothelialization was confirmed on the surface of the stent graft on the lumen side. At 1 and 3 months, all treated aneurysms with enough patent parent arteries were filled with organized tissues and completely occluded. CONCLUSION: Our developed stent graft appears to be promising for the treatment of aneurysms, especially with respect to immediate termination of blood inflow and early endothelialization in the neck of the aneurysm.

A recurrent intradural cervical neurenteric cyst operated on using an anterior approach: a case report.

The neurenteric cyst is an uncommon congenital lesion. In most reported cases, it has been operated on via a posterior approach using a laminectomy, despite the fact that the cyst is usually located ventral to the spinal cord. Reports have shown that early postoperative results have been good with the posterior approach, but very few studies of the long-term postoperative recurrence of neurenteric cysts have been conducted. Here, we report on a case of recurrent neurenteric cyst that was operated on using an anterior approach.A 42-year-old woman presented with a cervical neurenteric cyst that had recurred eight years after its partial removal via a posterior approach. The patient complained of pain on the lateral side of her upper arms, and an magnetic resonance imaging showed that the recurrent cyst was located ventral to the spinal cord and compressed the cord dorsally at the C4-6 level. The patient was operated on via an anterior approach using a vertebrotomy at the lower half of C5 and the upper half of C6. The cyst was attached to the spinal cord firmly and was subtotally removed, with the thickest portion adhering to the cord not being removed. The caudal end of the cyst was observed with the assistance of a rigid endoscope.A neurenteric cyst may recur after partial removal, and the patient's condition may deteriorate during postoperative follow-up. The anterior surgical approach provides good visualization and facilitates safe removal of the lesion.

Fabrication of micropored elastomeric film-covered stents and acute-phase performances.

To prevent thrombus formation in the acute phase and restenosis in the subacute to chronic phase after stenting of atherosclerotic arteries, we developed a covered stent with a micropored elastomeric film, the blood-contacting surface of which was coated with a photocured gelatin layer immobilized with heparin. Segmented polyurethane (SPU) film (30 microm in wall thickness) as a cover material was multiply micropored by excimer laser-directed microprocessing (pore diameter, 30 microm; interpore distance, 125 microm). An aqueous mixed solution of benzophenone-derivatized gelatin and heparin was coated on the micropored SPU film. Upon ultraviolet light irradiation, a thin layer of a gelatin gel immobilized with heparin was formed and simultaneously fixed on the SPU film. The fully covered stents were assembled by wrapping a balloon-expandable stent with gelatin/heparin gel-layered SPU film and subsequently suturing and then gluing. To assess the validity of this covered stent in vivo, "half-covered" stents, in which half at the distal side was covered with the gel-layered SPU film, was implanted in rabbit common carotid arteries (about 3 mm in diameter). After 3 months of implantation, all the half-covered stents (n = 7) were patent. Regardless of the covered or noncovered region of the stents, the entire luminal surface of the stents was fully endothelialized and a thin neointimal tissue was formed. The potential advantages of a covered stent as designed above are discussed.

Operative findings in cases of trigeminal neuralgia without vascular compression: proposal of a different mechanism.

Trigeminal neuralgia is known to be caused by vascular compression at the trigeminal root entry zone (REZ) and microvascular decompression provides good outcome in most of cases. However, in some cases, no vascular compression was observed at the REZ. Over the last 2(1/2) years, the first author operated on 53 cases of trigeminal neuralgia with microvascular decompression and encountered nine cases where no offending vessels were noted at or near the REZ. They were divided into two groups: five cases involving an initial operation and four cases involving a second operation. In the former, arachnoid thickening, angulation or torsion of the root axis were common findings. Dissection of thick arachnoid around the root along the whole length reversed the root to be straight and flaccid. Complete pain relief was noted in four of five cases. In one case of atypical pain, constant facial pain remained. In the latter four cases, where the first operations were done more than 4 years before, thick granulation was noted around REZ without new offending vessels in two cases. In the remaining two cases, where no offending vessels were noted in the first operation, thick adhesion of a distal portion of the root with dura on the pyramidal bone was noted. Meticulous dissection of t he whole length of the root was done and complete pain relief was obtained. Delayed but complete pain relief in these nine cases was noted. Based on operative findings, arachnoid thickening or granulomatous adhesion between the root and surrounding structures can cause an abnormal course of the trigeminal nerve root, which causes root angulation and/or torsion. They can also cause pulsatile movement of the trigeminal nerve root. This tethering effect can promote abnormal root stretching force, especially at REZ, which might promote hyperexitability of the nerve. This speculative mechanism suggests that it is important to make the root free along the entire length, especially at its distal portion in cases with no offending vessels.