Biomedical subjects

Akira Hagiwara

Publications and source records attributed to Akira Hagiwara.

8 recordsLinked to original sources

PubMed2006

A three-dimensional-weighted cone beam filtered backprojection (CB-FBP) algorithm for image reconstruction in volumetric CT-helical scanning.

Based on the structure of the original helical FDK algorithm, a three-dimensional (3D)-weighted cone beam filtered backprojection (CB-FBP) algorithm is proposed for image reconstruction in volumetric CT under helical source trajectory. In addition to its dependence on view and fan angles, the 3D weighting utilizes the cone angle dependency of a ray to improve reconstruction accuracy. The 3D weighting is ray-dependent and the underlying mechanism is to give a favourable weight to the ray with the smaller cone angle out of a pair of conjugate rays but an unfavourable weight to the ray with the larger cone angle out of the conjugate ray pair. The proposed 3D-weighted helical CB-FBP reconstruction algorithm is implemented in the cone-parallel geometry that can improve noise uniformity and image generation speed significantly. Under the cone-parallel geometry, the filtering is naturally carried out along the tangential direction of the helical source trajectory. By exploring the 3D weighting's dependence on cone angle, the proposed helical 3D-weighted CB-FBP reconstruction algorithm can provide significantly improved reconstruction accuracy at moderate cone angle and high helical pitches. The 3D-weighted CB-FBP algorithm is experimentally evaluated by computer-simulated phantoms and phantoms scanned by a diagnostic volumetric CT system with a detector dimension of 64 x 0.625 mm over various helical pitches. The computer simulation study shows that the 3D weighting enables the proposed algorithm to reach reconstruction accuracy comparable to that of exact CB reconstruction algorithms, such as the Katsevich algorithm, under a moderate cone angle (4 degrees) and various helical pitches. Meanwhile, the experimental evaluation using the phantoms scanned by a volumetric CT system shows that the spatial resolution along the z-direction and noise characteristics of the proposed 3D-weighted helical CB-FBP reconstruction algorithm are maintained very well in comparison to the FDK-type algorithms. Moreover, the experimental evaluation by clinical data verifies that the proposed 3D-weighted CB-FBP algorithm for image reconstruction in volumetric CT under helical source trajectory meets the challenges posed by diagnostic applications of volumetric CT imaging.

Algorithms↗

PubMed2005

A three-dimensional weighted cone beam filtered backprojection (CB-FBP) algorithm for image reconstruction in volumetric CT under a circular source trajectory.

The original FDK algorithm proposed for cone beam (CB) image reconstruction under a circular source trajectory has been extensively employed in medical and industrial imaging applications. With increasing cone angle, CB artefacts in images reconstructed by the original FDK algorithm deteriorate, since the circular trajectory does not satisfy the so-called data sufficiency condition (DSC). A few 'circular plus' trajectories have been proposed in the past to help the original FDK algorithm to reduce CB artefacts by meeting the DSC. However, the circular trajectory has distinct advantages over other scanning trajectories in practical CT imaging, such as head imaging, breast imaging, cardiac, vascular and perfusion applications. In addition to looking into the DSC, another insight into the CB artefacts existing in the original FDK algorithm is the inconsistency between conjugate rays that are 180 degrees apart in view angle (namely conjugate ray inconsistency). The conjugate ray inconsistency is pixel dependent, varying dramatically over pixels within the image plane to be reconstructed. However, the original FDK algorithm treats all conjugate rays equally, resulting in CB artefacts that can be avoided if appropriate weighting strategies are exercised. Along with an experimental evaluation and verification, a three-dimensional (3D) weighted axial cone beam filtered backprojection (CB-FBP) algorithm is proposed in this paper for image reconstruction in volumetric CT under a circular source trajectory. Without extra trajectories supplemental to the circular trajectory, the proposed algorithm applies 3D weighting on projection data before 3D backprojection to reduce conjugate ray inconsistency by suppressing the contribution from one of the conjugate rays with a larger cone angle. Furthermore, the 3D weighting is dependent on the distance between the reconstruction plane and the central plane determined by the circular trajectory. The proposed 3D weighted axial CB-FBP algorithm can be implemented in either the native CB geometry or the so-called cone-parallel geometry. By taking the cone-parallel geometry as an example, the experimental evaluation shows that, up to a moderate cone angle corresponding to a detector dimension of 64 x 0.625 mm, the CB artefacts can be substantially suppressed by the proposed algorithm, while advantages of the original FDK algorithm, such as the filtered backprojection algorithm structure, 1D ramp filtering and data manipulation efficiency, are maintained.

Algorithms↗

PubMed2005

Application of a rapid-prototyped temporal bone model for surgical planning.

CONCLUSION: This 3D prototyped model constructed using a selective laser sintering method serves as a good material for surgical simulation of a malformed ear. OBJECTIVE: In order to perform surgery of the malformed ear, a thorough understanding of the anatomy of the ear is required, together with sufficient experience. The aim of this study was to investigate the validity of a prototyped temporal bone model for surgical simulation. MATERIAL AND METHODS: Simulated 3D models of two cases of congenital aural atresia were prototyped using a selective laser sintering method. Conventional surgical instruments were used to dissect the models. RESULTS: Abnormal structures of the middle ear, such as the ossicles, labyrinth and facial nerve, were identified by dissecting the model. Presurgical dissection informed the surgeon of the optimum orientation for surgery. The model was disinfected and could be handled by the surgeon in the operating room. Surgery could be carried out safely although in one case it was canceled because of the highly abnormal location of the middle ear cleft and facial nerve.

Adult↗

PubMed2004

Rapid prototyping of temporal bone for surgical training and medical education.

OBJECTIVE: The skills of ear surgery are best developed by dissecting a temporal bone. However, only a limited number of trainees can be afforded this opportunity because of the scarcity of available bones. The aim of this study was to investigate the validity of a prototype temporal bone model for surgical training and education. MATERIAL AND METHODS: A simulated 3D model of a human temporal bone was made using a selective laser sintering method. The powder layers were laser-fused based on detailed CT data and accumulated to create a 3D structure. Conventional surgical instruments were used to dissect the model under a microscope. RESULTS: The model was as hard as real bone and surface structures were accurately reproduced. The model could be shaved using a surgical drill, burr and suction irrigator in the same way as a real bone. The malleus and incus were reproduced. The semicircular canals and the oval and round window niches were identified. Cavity structures, such as the semicircular canal, vestibule, antrum and air cells, were filled with powder which had to be removed using a pick and suction irrigator during dissection. A magnified model was useful for educating medical students. CONCLUSION: This prototype 3D model made using selective laser sintering serves as a good educational tool for middle ear surgery.

Humans↗

PubMed2004

Rapidly prototyped temporal bone model for otological education.

The anatomy of the temporal bone is extremely complicated. If a three-dimensional model could be simulated, it would greatly contribute to the stereoscopic understanding of anatomy and surgery. A simulated three-dimensional model of a human temporal bone was prototyped using the selective laser sintering method. The model could be shaved using a surgical drill in the same way as in real surgery. A magnified model was particularly useful for the instruction of anatomy and surgery. When a translucent area was selected, a bony labyrinth could be created together with an internal auditory meatus and facial nerve, which also contributed to the easy understanding of the inner ear structure. The three-dimensional prototyped model using selective laser sintering serves as a good educational material for middle ear anatomy and surgery.

Humans↗

PubMed2003

Comparison of growth hormone-producing and non-growth hormone-producing pituitary adenomas: imaging characteristics and pathologic correlation.

PURPOSE: To identify characteristic features of growth hormone (GH)-producing pituitary adenomas. MATERIALS AND METHODS: A total of 174 pathologically proven pituitary adenomas were evaluated retrospectively on magnetic resonance (MR) images to determine the signal intensity (on T2-weighted images), maximum diameter, and amount of suprasellar and infrasellar extension. For microadenomas, sellar depth was also measured. GH-producing adenomas were classified at histologic evaluation as densely or sparsely granulated. Specimens from 38 adenomas were stained to assess the amounts of fibrous tissue, iron, and amyloid they contained. Results were correlated with the size and hormonal activity of adenomas by using the chi2, unpaired t, and Mann-Whitney U tests. RESULTS: Among 174 pituitary adenomas, 42 were GH-producing adenomas. Of these, 16 were densely granulated, and 24 were sparsely granulated (two histologic specimens were lost). Signal intensity was evaluated among 153 adenomas. On T2-weighted MR images, hypointensity was seen more commonly in adenomas that produced GH (16 of 40 cases [40%]; P <.001) than in those that did not; hypointensity was nearly exclusive to densely granulated GH-producing adenomas. The amounts of amyloid, fibrous tissue, and iron contained in adenomas demonstrated little relationship with signal intensity. Average suprasellar extension was significantly smaller in adenomas that produced GH (-0.8 mm) than in those that did not (5.3 mm) (P <.001). GH-producing adenomas tended to demonstrate infrasellar extension rather than suprasellar extension. Average sellar depth associated with GH-producing microadenomas (13.3 mm) was significantly greater than for non-GH-producing microadenomas (9.7 mm; P <.001). CONCLUSION: Characteristic features regarding growth direction and T2 signal intensity can be identified for GH-producing adenomas.

Adenoma↗

PubMed2002

A case of laryngeal aspergillosis following radiation therapy.

Primary laryngeal aspergillosis is extremely rare. It is commonly seen as a part of a systemic infection involving the respiratory system in an immunocompromised host. Differential diagnosis is important, as the clinical symptoms are similar to those of malignant laryngeal disease. We describe a 73-year-old man with a history of hoarseness. He had a history of radiotherapy for laryngeal squamous cell carcinoma and had a history of diabetes. Direct laryngoscope and biopsy confirmed the diagnosis of aspergillus. We cauterized the lesion with a CO(2) laser. In the present case, irradiation seemed to have played a more important role in the onset of this disease rather than diabetes.

Aged↗

PubMed2000

Inconsistencies of Microcalcification Specks in Phantoms Approved by the American College of Radiology for Mammography Accreditation.

PURPOSE: To quantitatively demonstrate inconsistencies in microcalcification specks in RMI-156 phantoms approved by the American College of Radiology (ACR) for use with their mammography accreditation program. MATERIALS AND METHODS: Signal intensities of the largest three specks (C1, 540 &mgr;m; C2, 400 &mgr;m; C3, 320 &mgr;m) were measured on images of 14 RMI-156 (version 4) phantoms. Three images were analyzed per phantom: a packaged image of the wax plate and two phantom images obtained at an optical density of 1.2 to 1.3. Phantom images were digitized using a VXR-12 scanner at a resolution of 85 &mgr;m and 8 bit/pixel. Speck signals were measured as the average pixel values using the NIH Image program (version 1.61). RESULTS: Signal intensities of specks measured on phantom images were consistent with those measured on wax-plate images, with an average correlation coefficient of 0.898 for the C1 groups and of 0.794 for the C3 groups. Overlap of speck sizes was found between different groups. Speck signals of some inserts showed considerable inconsistencies within a group. In some phantoms, signal intensities of specks in different groups overlapped to each other, and C1 and C2 groups were not clearly separated. In all 14 phantoms, speck signal intensities of the C3 group had a between-phantom variance which was larger than the within-phantom variance. CONCLUSION: Microcalcification specks in RMI-156 phantoms of the same version were found to be substantially inconsistent in terms of size and intrinsic signal intensity. As lack of uniformity in specks within a phantom and between phantoms is not appropriate as a standard of image quality control, further quality control is apparently needed in manufacturing RMI-156 phantoms and also in approving specific phantoms.

Journal Article↗