Ray Projection Research Articles

Quickly select heliostat candidates and design pattern-free layout using geometric projection method

Central receiver system is one of the most promising solar energy harvesting technologies, which focuses sunlight onto the receiver through heliostats to generate high temperatures for thermal cycling. The optimal layout of the heliostat plays a crucial role, but the pattern-free heliostat field layout requires multiple uses of computationally intensive shadowing and blocking efficiency, which is highly time-consuming. In this work, a new geometric projection method, Projection radius method (PRM), is proposed. It includes two aspects: (i) Quickly and effectively selecting heliostat candidates with shadowing and blocking potential by the incident and reflected ray projection radius; (ii) Designing the pattern-free heliostat field layout by employing overlap radius instead of shadowing and blocking efficiency. The results indicate that, compared to traditional methods, when designing 2650 heliostats, (i) the calculation time for optical efficiency was reduced by 63%; (ii) optical efficiency increased by 1.23%, and designing a pattern-free layout took only 2.78 h. These advancements facilitate the efficient design of large-scale pattern-free heliostat field layouts.

A challenging case of scleral buckle-related restricted strabismus with unexpected good postoperative outcomes: A case report

Abstract Strabismus surgery in a scleral buckle patient is a challenging task that requires precise planning and meticulous surgical skills to accomplish a successful outcome. We report a case of a 32-year-old male who presented with complaints of diminution of vision in the right eye (RE) for 23 years and outward deviation of RE for 5 years after blunt trauma with a ball. The patient was diagnosed with RE total retinal detachment (RD) with traumatic retinal dialysis. He underwent scleral buckling as RD surgery in 2004 followed by silicon oil removal 6 months later elsewhere. On ocular examination of the RE, the best corrected visual acuity was perception of light with accurate projection of rays in all four quadrants, there was grade III relative afferent pupillary defect with an exotropia of 20° on Hirschberg test. The prism bar reflex test revealed an exotropia of 50 prism diopters (PD) [Figure 1]. An anterior segment examination revealed posterior subcapsular and cortical cataracts. After taking a retina clinic opinion, the patient underwent uneventful RE cataract surgery with in-bag implantation of a foldable implant cataract surgery first, followed by strabismus surgery under a guarded visual prognosis. Clinically significant adhesion and the presence of the scleral buckle posed a magnificent challenge during the strabismus surgery. The plan was improvised to 8 mm lateral rectus recession with 4 mm hang loose recession irrespective of a large deviation under local anesthesia. To our surprise, a satisfactory primary position alignment within 10 PD (orthophoria) was achieved, which was maintained on subsequent follow-up visits. We report an interesting and challenging case of restrictive strabismus due to scleral buckle which emphasizes that surgical procedures and their outcomes may not always align with expectations. Therefore, it is necessary to adopt a flexible and customized approach to effectively manage such instances.

Digital Breast Tomography Reconstruction Based on Focusing Layer Separation from Multi-Angle X Ray Projections Using Blind Source Separation

Digital Breast Tomography Reconstruction Based on Focusing Layer Separation from Multi-Angle X Ray Projections Using Blind Source Separation

Clinical Outcome of Amniotic Membrane Transplantation in Chemically Injured Eyes

Purpose: To evaluate the clinical outcome of Amniotic Membrane Transplantation (AMT) in chemically injured eyes for ocular surface reconstruction. Methods: A prospective study of 30 consecutive chemically injured eyes was performed from December 2022 to May 2023 in National Institute of Ophthalmology & Hospital (NIO&H), Dhaka, Bangladesh. Twenty-seven patients (30 eyes having corrosive chemical injuries) were included in the study according to the inclusion & exclusion criteria. AMT was performed within 21 days of injury by single surgeon with modified surgical procedure. Post operative evaluation was done by Snellen chart, slit lamp biomicroscope and Schirmer-II test. Results: After 3 months of AMT, there was no pain or inflammation. Improvement of vision found in 20 (66.67%) of 30 eyes, 4 (13.33%) eyes of rest 10 eyes showed inaccurate Projection of Rays (PR) vision and rest 6 (20.0%) eyes of rest 10 eyes found deteriorated vision. Epithelialization occurred in all eyes. Twenty-four (80.0%) eyes had limbal stem cell deficiency and they experienced superficial corneal vascularization. Symblepharon was seen in 18 (60.0%) eyes, 6 (20.0%) of these 18 eyes developed marked conjunctival shortening with ankyloblepharon. None of the eyes showed perforation. Conclusions: AMT increases patient comfort and reduces inflammation. In mild burns, AMT alone restores corneal and conjunctival surfaces. In moderate to severe burns, it reduces conjunctival scarring sequelae, but does not prevent the sequelae of limbal stem cell deficiency that requires further limbal stem cell transplantation. In the acute stage, AMT has a protective role against the progressive melting and perforation. J.Natl.Inst.Ophthalmol.2023;6(1): 21-26

Ocular involvement—An unusual initial presentation of chronic myeloid leukemia: A case report

ABSTRACT Chronic myeloid leukemia (CML) patients frequently exhibit systemic symptoms such as fatigue, abdominal discomfort, weight loss, and fever but rarely can have atypical initial presentation in the form of ophthalmic manifestations, which can precede the diagnosis of the primary malignancy. We describe a case of a 29-year-old male who presented in our ophthalmology out-patient department (OPD) with complaints of painless, diminution of vision, which was sudden in onset in right eye (RE) and loss of vision in left eye (LE) for four and seven days, respectively. There had been a history of loss of weight and appetite for the past 2 months. The visual acuity (VA) recorded was finger counting two meters in RE and perception of light in LE with an inaccurate projection of rays in both eyes (BE). The anterior segment evaluation of both eyes (BE) was normal. Fundus revealed multiple elevated yellow subretinal lesions with exudative detachment in the RE and no view in the LE. Ultrasound-Brightness (USG B) scan in the LE revealed multiple hyperreflective echoes likely vitreous hemorrhage. Optical coherence tomography (OCT) showed subretinal hyperreflectivity with surrounding edema in RE suggestive of leukemic infiltrates. On further systemic investigations, chronic myeloid leukemia-chronic phase (CML-CP) was detected; hence, the diagnosis of RE exudative retinal detachment (RD) and LE vitreous hemorrhage with CML-CP was made. Ophthalmic involvement is more often seen in acute than chronic leukemia, which makes the diagnosis challenging. We describe a unique case of a young patient with CML-CP who initially presented with ocular involvement preceding systemic diagnosis. This case report illustrates the importance of a primary care physician or an ophthalmologist in the early diagnosis and prompt management of hematological malignancy, as ophthalmic manifestations may be a rare initial presenting feature in CML-CP. These conditions require urgent referral to a hematologist by a primary care physician in the view of early commencement of therapy.

Auro-Keratoprosthesis for Visual Rehabilitation in Ocular Graft Versus Host Disease

Abstract A 36-year-old male presented with right eye graft melt post-penetrating keratoplasty (PK) for Aspergillus infection. The patient had a history of acute lymphocytic leukemia and had undergone a bone marrow transplant. He developed ocular graft versus host disease (GVHD) in both eyes and tissue adhesive application had to be performed for bilateral corneal melt. The right eye developed fungal keratitis, necessitating therapeutic keratoplasty. At presentation, the visual acuity was perception of light with an accurate projection of rays in the right eye and finger counting at 1 m in the left eye. An anterior chamber tap showed no organism on culture. Considering the non-ambulatory state of the patient and the need for early visual rehabilitation due to deteriorating mental well-being, a keratoprosthesis (KPro) surgery with amniotic membrane grafting was performed in the right eye. By post-operative day 20, the patient achieved a best-corrected visual acuity of 20/20. A PK was later performed in the other eye. It is conventionally believed that KPro is the last resort for bilateral corneal blindness and is commonly performed after multiple PK grafts have failed. However, this case highlights another indication of KPro in ocular GVHD; the rehabilitation of vision when PK will not work. In addition, this case illustrates the difference in the long-term outcomes between the two eyes, one that underwent early KPro surgery and the other that underwent early PK in ocular GVHD.

Management of perforated corneal ulcer with iris prolapse by cyanoacrylate glue: A case report

We report a rare case of perforated corneal ulcer due to recurrent viral keratitis with stromal necrosis and iris prolapse. The patient was 75 years old farmer, normotensive, diabetic, and presented with complaints of pain, watering, photophobia, redness and dimness of vision in the left eye. The left eye's visual acuity was perception of light and projection of rays in all four quadrants. Slit lamp examination found swollen eyelids, matted eyelashes, congested conjunctiva, seidel test positive, an inferonasal corneal perforation, shallow anterior chamber, irregular pupil, and prolapse of the iris through the perforated cornea. The patient was diagnosed with a left-sided perforated corneal ulcer (recurrent viral keratitis with stromal necrotizing variety) having iris prolapse. The perforation was sealed by cyanoacrylate glue and a soft bandage contact lens. This improved the patient’s condition. Early medical and surgical interventions thus can save vision as well as the eyeball.

Detection & Quantification of Lung Nodules Using 3D CT images

In computer vision image detection and quantification play an important role. Image Detection and quantification is the process of identifying nodule position and the amount of covered area. The dataset which we have used for this research contains 3D CT lung images. In our proposed work we have taken 3D images and those are high-resolution images. We have compared the accuracy of the existing mask and our segmented images. The segmentation method that we have applied to these images is Sparse Field Method localized region-based segmentation and for Nodule detection, I have used ray projection. The ray projection method is efficient for making the point more visible by its x, y, and z components. like a parametric equation where the line crossing through a targeted point by that nodule is more dominated. The Frangi filter was to give a geometric shape to the nodule and we got 90% accurate detection. The high mortality rate associated with lung cancer makes it imperative that it be detected at an early stage. The application of computerized image processing methods has the potential to improve both the efficiency and reliability of lung cancer screening. Computerized tomography (CT) pictures are frequently used in medical image processing because of their excellent resolution and low noise. Computer-aided detection systems, including preprocessing and segmentation methods, as well as data analysis approaches, have been investigated in this research for their potential use in the detection and diagnosis of lung cancer. The primary objective was to research cutting-edge methods for creating computational diagnostic tools to aid in the collection, processing, and interpretation of medical imaging data. Nonetheless, there are still areas that need more work, such as improving sensitivity, decreasing false positives, and optimizing the identification of each type of nodule, even those of varying size and form.

Conversion of underwater concrete images to air in detection of hydraulic structures

Taking underwater concrete images with an optical camera is an important measure for underwater defect detection. However, the underwater low-light environment and light refraction on the surface of different media result in poor image quality. In order to make the collected underwater images effectively reflect the real situation of underwater concrete defects, we propose an image conversion algorithm combining underwater image color enhancement and refraction distortion correction, which can convert underwater images into aerial equivalent images. In this paper, two conversion models of underwater image to air conversion are proposed, one of which models the refractive distortion of the underwater multilayered media through the ray projection method to correct the refractive distortion of underwater images and image field of view (FOV) conversion. The other is that by analyzing the problem of low image-imaging quality and loss of edge information due to the uneven illumination environment underwater, we process the dark channel priority adaptive enhancement algorithm to improve underwater image quality. The experimental results from real scenes show that the imaging quality of underwater images is improved by converting underwater images to air. The pixel error of images converted into the air is ⩽1 pixel, and the FOV error of images is ⩽8.5%. The high-precision underwater image conversion provides strong support for subsequent underwater measurement.

Invasive Sinu-Naso-Orbital Aspergilloma Following Dacryocystorhinostomy in an Immunocompetent Patient: A Rare Case Report and Literature Review

Background: Invasive sinu-naso-orbital aspergilloma is a rare disease with variable clinical features, but in an immunocompetent patient, it is rarely considered and often resulted in a poor prognosis due to its diagnostic and therapeutic challenges. In this article, we report a rare case of invasive sinu-naso-orbital aspergillosis with intracranial extension following dacryocystorhinostomy. To the best of our knowledge, this is the only reported case in the past 109 years. Case Description: A 61-year-old normotensive nondiabetic male was referred to us from an ophthalmologist with complaints of retro-orbital pain followed by progressive dimness of vision and later blindness on right eye after dacryocystorhinostomy. Diagnosis and Intervention: His MRI reveals an isointense lesion in the T1W and T2W images in the right maxillary, ethmoidal sinus with orbital and retro-orbital, and intracranial extension with heterogeneous contrast enhancement. A radiologist suggested a case of inflammatory pseudotumor, and initially he was treated with steroids due to a lack of clinical response; later, antifungal was given, but the patient still was nonresponsive. A right pterional craniotomy was performed on the patient to access the optic nerve and perform the biopsy. Aspergillus infection was seen by histopathology. Postoperatively, he was treated with voriconazole. Lessons: In immunocompetent individuals, invasive sino-orbital aspergillosis is uncommon. For effective care, early diagnosis is essential. Our advice is that a patient with vague symptoms or retro-orbital discomfort should encourage the doctor to investigate this diagnosis due to the diagnostic difficulties and greater mortality and morbidity rates. Abbreviations: DCR: dacryocystorhinostomy, PL: Perception of light, PR: Projection of rays

Clinical outcome of Tenon’s patch graft and bandage contact lens in cases of corneal perforation

Background: Corneal perforation is a leading cause of ocular morbidity around the world. It may occur due to trauma to the eye, keratitis, and many other conditions. Any corneal perforation should be treated immediately and promptly to avoid complications and subsequently corneal blindness.Objective: To describe effectiveness of using autologous Tenon’s tissue along with bandage contact lens to manage corneal perforations less than 3 mm in size.Methods: Tenon’s patch graft was done in five cases of corneal perforation. Informed consent was obtained from the subjects after explanation of the nature and possible consequences of the study and this study was approved by ethical committee.Results: Of the five patients the first patient she showed good integration of the Tenon’s Patch Graft (TPG). She had a vision of Perception of Light+ and accurate projection of rays after a period of 5 months post procedure. The wound healed with a glaucomatous scar. Case two had a vision of counting fingers close to face after five months. Case three showed good integration of the TPG. He had a vision of 6/60 accurate after a period of three months post procedure. In case four anterior chamber was shallow, post patch integrity was not maintained. Patient was later considered for penetrating keratoplasty. Case five showed integration of TPG after one week postop with vision counting fingers at 6 meters.Conclusion: We conclude that Tenon's Patch Graft with bandage contact lens is an effective technique in the treatment of corneal perforations. Using this, the integrity of the eyeball can be maintained without any danger of graft rejection since the tissue is autologous. This technique can be used effectively in places where resources are scant.

Posterior lens capsular neovascularization in the absence of any risk factors

Neovascularization of the posterior capsule after uncomplicated cataract surgery is a rare occurrence. This case entails a similar presentation, however, in the absence of any known predisposition. An 80-year-old male presented with painless progressive diminution of vision in his right eye after having undergone uncomplicated cataract surgery with good visual recovery 3 years back. He had a visual acuity of counting fingers close to face with accurate projection of rays with no further improvement. He was found to have posterior capsular opacification with capsular neovascularization. He was managed with intravitreal ranibizumab followed 2 weeks later by neodymium: yttrium-aluminum-garnet capsulotomy clearing the visual axis. His visual acuity improved; however, the best-corrected visual acuity was 6/60 due to an epiretinal membrane.

Management Challenge: A Case of Aniridia and Aphakia with Secondary Glaucoma in Sclerokeratoplasty

A patient presented to us with post-infectious keratitis and a large anterior staphyloma in the left eye with vision as low as only the perception of light and accurately determining the projection of rays. A B-scan showed no abnormality in the posterior segment. Sclerokeratoplasty with an 11-mm graft with aniridia and aphakia was done. On 4 weeks of follow-up, intraocular pressure (IOP) was 39 mmHg on applanation tonometry, for which medical management was tried using a combination regime that was insufficient, following which a series of management approaches like trabeculectomy and Ahmed glaucoma valve (AGV) implant was done (in superotemporal quadrant). Unfortunately, recurrent exposures of the AGV tube were encountered, which were managed using different graft materials one after the other but were unsuccessful. Ultimately, AGV explantation and reinsertion at another site (in inferotemporal quadrant) was tried, which led to salvaging the eye with well controlled IOP, clear graft, and good visual function (best corrected visual acuity of 6/12p with +12.00/+1.50 × 90◦ ). The purpose of this article was to highlight that despite multiple complications encountered in a single case, a careful sequential approach, good surgical skills, and a never giving up attitude lead to excellent results.

Analysis of 74 Open Globe Injuries Requiring Vitreo-Retinal Intervention and Its Correlation with Ocular Trauma Score

Aim: Retrospective study of 74 eyes with open globe injuries requiring V-R Intervention & its correlation with ocular trauma score.
 Results: Commonest cause of injury: Hammer-chisel/stone in 32.43% (24) & Thorn/wooden stick 27% (20). Average age-30.5yrs. Average interval between trauma & intervention was -10.04days (4hrs – 52days).
 Discussion: Delay of presentation to ophthalmologist has lot of significance,high incidence of endophthalmitis & retinal detachment compared to other studies. Surgical outcome shows lower incidence of NO Light Perception & Significant reduction in number of cases with </=HM. Patients had better prognosis & visual outcome, higher incidence of 1/200- 20/50; 35.14% cases with >20/200. 60% of our cases had traumatic cataract, visual acuity may be underestimated in traumatic cataract. Faulty Projection of rays probably would be better criteria than RAPD. Extension of wound beyond pars plana, and aniridia (6.7%) are important risk factor.
 Conclusion: Modification of raw points is recommended in OTS criteria in Indian scenario.

Modelling and Image Reconstruction Evaluation of a Scintillation Camera with Silicone Photomultiplier.

Background: Recent research on photon detection has led to the introduction of a silicone photomultiplier (SiPM) that operates at a low voltage and is insensitive to magnetic fields. Objective: This work aims to model a scintillation camera with a SiPM sensor and to evaluate the camera reconstructed images from gamma ray projection data.Material and Methods: The type of study in this research is experimental work and analytical. The scintillation camera, modelled from an SiPM sensor array SL4-30035, coupled with a scintillation material Caesium Iodide doped with Thallium (CsI(Tl)), is used in the experimental part. The performance of the camera was evaluated from reconstructed images by a back-projection technique of a radioactive source Caesium-137 (Cs-137).Results: The experiments conducted with a 1 µCi Cs-137 radioactive source have revealed that the bias voltage (Vbias) of the SiPM needs to be set to 27.8 V at an operating temperature between 43 °C to 44 °C. The radioactive source has to be placed within a 1 cm distance from the sensor to obtain the optimum projection data. Finally, the back-projection technique for image reconstruction with linear interpolation pre-processing has revealed that the Ram-Lak filter produces a better image contrast ratio compared to others.Conclusion: This research has successfully modelled a scintillation camera with SiPM that was able to reconstruct images with an 86.4% contrast ratio from gamma ray projection data.

Comparative Assessment of Hallux Rigidus using Conventional Radiograph and Weightbearing CT

Category:Midfoot/ForefootIntroduction/Purpose:The etiology of hallux rigidus (HR) is not well understood and Its association with first-ray hypermobility, hallux valgus and metatarsus primus elevatus (MPE) has not been clearly proven. MPE, elevated first metatarsal has been a topic of debate since Lambrinudi`s first description. Recent studies have supported MPE in hallux rigidus by measuring with various methods on wightbearing lateral radiographs, but there are limitations of conventional radiography due to variation in X- ray projection and superimposed metatarsals regardless of the methods of measurement. Our objective was to assess MPE and other associated parameters with hallux rigidus via radiography and WBCT for convergent validity and to evaluate the use of classification system used in conventional radiography with WBCT.Methods:This is a single-center, retrospective study from prospectively collected data. 20 symptomatic hallux rigidus patient with weightbearing radiograph and WBCT were enrolled from October 2014 to December 2020. Measured parameters included hallux valgus angle (HVA), intermetatarsal angle (IMA), hallux interphalangeal angle (HIPA), distal metatarsal articular angle (DMAA), 1st TMT joint version, First and second metatarsal lengths, Metatarsus adductus angle, 2nd cuneiform-2nd metatarsal angle, Talus-1st Metatarsal Angel, First and second metatarsal declination angles, and MPE. MPE was measured as the direct distance between 1st and 2nd metatarsals (modified Horton index). All patients were graded according to the radiographic criteria of Coughlin and Shurnas classification on radiographs and WBCT, separately. Paired T-test was performed to compare radiographic measurements with WBCT.Results:Mean age was 55.9, 12 males and 8 females. HVA (15.73 in X-ray vs 14.04 in WBCT), AP first TMT version (16.25 vs 16.47), 2nd cuneiform-2nd metatarsal angle (24.54 vs 26.60), Talus-1st Metatarsal Angel (-7.67 vs -7.89) were not different between radiograph and WBCT. MPE was measured higher in WBCT by 0.86 mm compared to radiograph. First metatarsal declination angle was lower in WBCT by 2.9° indicating increased MPE. When graded with radiographic findings, 5 (25%) patients were grade 1, 5 (25%) patients were grade 2 and 10 (50%) grade 3, when graded with WBCT, 1 (5%) patient had grade 1, 3 (15%) patients were grade 2 and 16 (80%) grade 3. Dorsal subluxation/translation of first metatarsal at first TMT joint was observed 3 (15%) in radiograph and 9 (45%) in WBCT.Conclusion:HVA, AP first TMT version, 2nd cuneiform-2nd metatarsal angle, Talus-1st Metatarsal Angel demonstrated consistent measurements in radiograph and WBCT. MPE was measured higher in WBCT when measured with direct distance (0.86 mm) between the first and second metatarsals using modified Horton index and first metatarsal declination angle (2.9°). When graded with WBCT, the subchondral cyst in the proximal phalanx and metatarsal head were better delineated leading to higher grade in WBCT. Further studies are needed for inter-rater reliability and discriminant validity of the measurements determined by differences between different groups (HR vs control).

Three-dimensional reconstruction of magnetic resonance images of carp brain for brain control technology

BackgroundIn the field of animal robot control, brain control technology is currently used to achieve control. It is usually necessary to accurately implant brain electrodes into the animal's brain movement area with the help of a brain stereotaxic apparatus, and apply electrical stimulation to achieve control of the animal. The prerequisite for accurate electrode implantation is to study the internal tissues of the carp skull. New MethodWith the help of 3.0 T magnetic resonance imaging (MRI) instrument and 8_CH MRI scanning coil, carp brain magnetic resonance images was obtained. The visualization tool package VTK and the marching cube algorithm were used for surface rendering, the ray casting algorithm was used for volume rendering and reconstruction. ResultsThe three-dimensional reconstruction results could show the carp skull surface contour and internal tissue details, and the measured coordinates after three-dimensional reconstruction of magnetic resonance images could be transformed into three-dimensional positioning coordinates suitable for brain stereotaxic apparatus. Comparison with existing methodsThe three-dimensional reconstruction images based on magnetic resonance could analyze the relative spatial position relationship between the surface structure of the carp's brain and the internal tissue at any angle, and the three-dimensional positioning coordinates of the brain could be obtained quickly and accurately. ConclusionsThe visualization of carp brain magnetic resonance images based on marching cubes algorithm and ray projection algorithm could obtain ideal reconstruction effects, which could be used in the brain control technology of carp robot.

Visual Outcome of Combined Descemet Stripping Endothelial Keratoplasty and Sutured Scleral Fixated Intraocular Lens in Endothelial Decompensation with Coexistent Aphakia or Intra Ocular Lens Subluxation

Purpose To elucidate visual outcome of patients after combined Descemet stripping endothelial keratoplasty (DSEK) with scleral fixated intra ocular lens (SFIOL) implantation in patients of endothelial decompensation with coexistent aphakia or lens subluxation. Materials and Methods A prospective interventional study of combined DSEK with sutured SFIOL in the patients who have undergone surgery at our center over 6-month follow-up period. Preoperative visual acuity and slit lamp findings were documented. Postoperative follow-up was done at days 1, 3, and 7 subsequently, months 1 and 3, and thereafter monthly till the sixth month. Results Mean age of the patients was 60.47 years. Six patients had aphakic bullous keratopathy, while 11 patients had pseudophakic bullous keratopathy with subluxated posterior chamber IOL (PCIOL). Preoperative visual acuity ranged from hand movements close to face (LogMar 2.4) with accurate projection of rays to 1/60 (LogMar 2) due to existing corneal edema and aphakia. Postoperatively uncorrected visual acuity at 6 months improved up to 6/36 (LogMar 0.8) in all cases. There was gradual improvement in corneal clarity and compactness during the follow-up. A good donor tissue endothelial count and an adequate IOP control were vital prognostic factors for the successful outcome. Conclusion This novel surgical merger reduces the complications of lenticule dislocation into vitreous and repeated surgeries and shows results akin to when performed in a staged manner.

Research on Improved Ray Casting Algorithm and Its Application in Three-Dimensional Reconstruction

Spinal pathology treatment has become an urgent issue to be solved. How to effectively prevent and treat spinal pathology has become a research hotspot in the field of surgery. Aiming at the problem of too long volume rendering time caused by the trilinear interpolation sampling method in the reconstruction and visualization of the vertebra 3D model, an improved ray projection algorithm is proposed to quickly reconstruct a 3D vertebra model from medical CT vertebra images. This method first classifies CT data, assigns corresponding color values and opacity transfer functions to different types of data, and then uses inverse distance-weighted interpolation (IDWI) sampling to replace the trilinear interpolation sampling method for the voxel where the sampling point is located to accelerate the interpolation operation. The color value and opacity of the sampling points are obtained, and finally, the attributes of all the sampling points are synthesized and calculated to obtain the final rendering effect, and the reconstruction of the three-dimensional vertebra model is completed. Experimental results show that the proposed method not only can obtain higher quality rendered images but also has a certain improvement in rendering speed compared with traditional algorithms.

New calculation method for exact length weighting factor in cone‐beam computed tomography

AbstractIn iterative reconstruction algorithms, it is very important to calculate the weighting factor quickly and accurately, which directly affects the reconstruction efficiency and accuracy of computed tomography images. In this paper, a new calculation method for accurate length weighting factor is developed. Firstly, the ray equation is determined according to the coordinates of the source and the ray's projection. Second, the intersections of the ray and the equidistant parallel planes along three coordinate axes are calculated, and the points intersecting with the reconstructed object are put into a set. Finally, when the X‐axis coordinates of all points in the set are different, the points are arranged according to their X‐axis coordinates; when the X‐axis coordinates of all points are same, the points are arranged according to their Y‐axis coordinates. The sorted point set is the intersections that the ray traverses the reconstructed object in sequence. The index and weighting factor of all voxels that the ray passes through can be determined by the sorted point set. Compared with the classical Siddon's method, it avoids the step of describing the intersections with parameters, and its calculation speed is increased by nearly 20%. The numerical simulations and real data reconstruction experiments are conducted to validate the proposed calculation method of exact length weighting factor.