Circular Tomography Research Articles

Photothermal effect in X-ray images for computed tomography of metallic parts: Stainless steel spheres.

The environmental impact on industrial X-ray tomography systems has gained its attention in terms of image precision and metrology over recent years, yet is still complex due to the variety of applications. The current study explores the photothermal repercussions of the overall radiation exposure time. It shows the emerging dimensional uncertainty when measuring a stainless steel sphere by means of circular tomography scans. The authors develop a novel frame difference method for X-ray radiographies to evaluate the spatial changes induced in the projected absorption maps on the X-ray panel. The object of interest has a simple geometry for the purpose of proof of concept. The dominant source of the observed radial uncertainty is the photothermal effect due to high-energy X-ray scattering at the metal workpiece. Thermal variations are monitored by an infrared camera within the industrial tomography system, which confines that heat in the industrial grade X-ray system. The authors demonstrate that dense industrial computed tomography programs with major X-ray power notably affect the uncertainty of digital dimensional measurements. The registered temperature variations are consistent with dimensional changes in radiographies and hence form a source of error that might result in visible artifacts within the 3D image reconstruction. This contribution is of fundamental value to reach the balance between the number of projections and radial uncertainty tolerance when performing analysis with X-ray dimensional exploration in precision measurements with industrial tomography.

Solving Traveltime Tomography with Deep Learning

This paper introduces a neural network approach for solving two-dimensional traveltime tomography (TT) problems based on the eikonal equation. The mathematical problem of TT is to recover the slowness field of a medium based on the boundary measurement of the traveltimes of waves going through the medium. This inverse map is high-dimensional and nonlinear. For the circular tomography geometry, a perturbative analysis shows that the forward map can be approximated by a vectorized convolution operator in the angular direction. Motivated by this and filtered back-projection, we propose an effective neural network architecture for the inverse map using the recently proposed BCR-Net, with weights learned from training datasets. Numerical results demonstrate the efficiency of the proposed neural networks.

The Application of Compressed Sensing for Photo-Acoustic Tomography

Photo-acoustic (PA) imaging has been developed for different purposes, but recently, the modality has gained interest with applications to small animal imaging. As a technique it is sensitive to endogenous optical contrast present in tissues and, contrary to diffuse optical imaging, it promises to bring high resolution imaging for in vivo studies at midrange depths (3-10 mm). Because of the limited amount of radiation tissues can be exposed to, existing reconstruction algorithms for circular tomography require a great number of measurements and averaging, implying long acquisition times. Time-resolved PA imaging is therefore possible only at the cost of complex and expensive electronics. This paper suggests a new reconstruction strategy using the compressed sensing formalism which states that a small number of linear projections of a compressible image contain enough information for reconstruction. By directly sampling the image to recover in a sparse representation, it is possible to dramatically reduce the number of measurements needed for a given quality of reconstruction.

Comparison of compact gamma cameras with 1.3- and 2.0-mm quantized elements for dedicated emission mammotomography

In an effort to image smaller breast lesions, two compact gamma cameras with different intrinsic NaI(Tl) pixel sizes are evaluated for use in the application specific emission tomography (ASET) system for dedicated mammotomographic emission imaging. Comparison measurements were made with two scintillator arrays having 1.3/spl times/1.3/spl times/6 mm/sup 3/ or 2.0/spl times/2.0/spl times/6 mm/sup 3/ elements on exactly the same set of PMTs, electronics and control/processing hardware. Uniformity, sensitivity and energy resolution were assessed with flood field phantoms. Spatial resolution measurements included: a /sup 99m/Tc (140 keV) activity filled capillary tube imaged in planar mode from 1-10 cm distance; two such tubes separated by 2 cm were also imaged with simple circular tomography from 3-7 cm radii-of-rotation (RORs); and a /sup 99m/Tc filled mini cold-rod phantom was imaged at 5 cm ROR with a simple circular orbit. Finally, a freely suspended and uniformly filled 950 mL breast phantom containing four fillable lesions (4-10 mm dia) was imaged with a lesion-to-uniform-background activity concentration ratio of 15:1, using simple and complex three-dimensional (3-D) orbits and minimal RORs. The measured sensitivity varied by the crystal fill-factor; uniformity had <4% variability; and mean energy resolutions of each camera were /spl les/12% full-width at half-maximum (FWHM). The planar spatial resolutions correspond to calculated values, with smaller pixels yielding 2%-13% better resolution with decreasing separation distance; tomographic results ranged from 3.2-5.2 mm FWHM at 3-7 cm, with nominally better contrast-resolution for the smaller pixel camera. Consistent with signal detection characteristics for these measurement conditions, quantitative SNRs and contrasts from lesion imaging with the uniform breast background illustrate better overall performance under nearly all conditions and for all lesions for the larger pixel camera.

Radiologic evaluation of dens fracture. Role of plain radiography and tomography.

A retrospective study of 50 dens fractures was performed. In 47 of 50 cases (94%), plain radiographs disclosed the fracture. Initial cross-table lateral view alone showed the fracture in 43 cases. In the remaining four cases, routine plain films revealed the fracture: open-mouth view in three cases and lateral skull view in one case. In 3 of 50 cases (6%), plain films were negative, and fractures were seen only on tomography. Conventional circular tomography was performed in 26 cases; results were divided into 3 categories according to the significance of the findings: Category I, tomography confirmed plain radiographic findings, but added no further information; Category II, tomography detected additional findings or showed the extent of injury better than plain radiography; Category III, fracture was only seen by tomography. There were 19 cases in Category I, 4 in Category II, and 3 in Category III. Careful evaluation of plain radiographs remains the primary method for diagnosis of dens fractures. Tomography should be performed whenever plain radiographs or clinical symptoms are suspicious for dens fracture. In addition, tomography is useful to define the fracture level and pattern, which are important factors in the management of these injuries.

Fast Circular Tomography Device for Cardiac Imaging: Image Deflection Mechanism and Evaluation

A circular tomography system for cardiac imaging is described and measurements of the detector system are presented. Fast tomographic motion is obtained with a custom-made rotating focal spot X-ray tube combined with servo-operated scanning mirrors that deflect the optical image between a large field of view image intensifier and television camera. The motion of the deflection mirrors is locked in frequency and phase to the position of the focal spot with precision analog electronics. Initial measurements on the system components indicate that circular tomograms of the beating heart can be obtained in 1/60 s at rates as high as 30/s. Image degradation due to focal spot tracking error is minimal; however, the optical temporal lag of a P-20 type image intensifier output phosphor results in a factor of three contrast loss for millimeter-sized objects. A linear system analysis in conjunction with the measured temporal step response of the phosphor is in good agreement with the magnitude of this contrast loss.

Selective plane removal in limited angle tomographic imaging.

A method of improving a planar image in limited angle tomography by removing blurred image information from selected out-of-focus planes is discussed. Focused tomosynthesized images rather than individual projections are used. The necessary equations for removing the information from either two or four adjacent planes, produced with a symmetrical, but otherwise arbitrary blurring function, are developed and specialized to the geometry of circular tomography. Results of a phantom experiment illustrating the technique are presented.

Rheumatoid arthritis of temporo-mandibular joint.

In a detailed study of 100 consecutive cases of rheumatoid arthritis, clinical abnormalities were present in the temporomandibular joints in 71.0 per cent of patients compared with 41.1 per cent of a group of matched controls. This difference is highly significant (P < 0.0005). Circular tomography was used to study the joints radiologically. By this technique, which does not appear to have been used previously in a study of this nature, 78.7 per cent of the rheumatoid patients' joints showed abnormalities compared with 33.9 per cent of the control joints. This difference is also highly significant (P < 0.0005). Certain clinical and radiological features appeared to be almost specific for rheumatoid arthritis and to correlate with increasing severity of the disease. Rheumatoid arthritis appears to affect the temporomandibular joint more commonly than was at one time thought.

Rheumatoid Arthritis of the Temporomandibular Joint

Abstract In a detailed study of 100 consecutive cases of rheumatoid arthritis, clinical abnormalities were present in the temporomandibular joints in 71.0 per cent of patients compared with 41.1 per cent of a group of matched controls. This difference is highly significant (P &amp;lt; 0.0005). Circular tomography was used to study the joints radiologically. By this technique, which does not appear to have been used previously in a study of this nature, 78.7 per cent of the rheumatoid patients' joints showed abnormalities compared with 33.9 per cent of the control joints. This difference is also highly significant (P &amp;lt; 0.0005). Certain clinical and radiological features appeared to be almost specific for rheumatoid arthritis and to correlate with increasing severity of the disease. Rheumatoid arthritis appears to affect the temporomandibular joint more commonly than was at one time thought.

Circular tomography of the temporomandibular joint: A critical evaluation of the accuracy and reproducibility of the technique

Circular tomography has been applied to the study of the temporomandibular joint. In order to assess the method, two sets of radiographs were obtained in twenty-one subjects, including patients suffering from different joint diseases. The results showed that the radiologic technique was reproducible and that accurate measurements could be made from the radiographs.

Radiology of the temporomandibular joint: A comparison of circular tomography with orthopantomography and lateral transcranio-oblique radiography

Circular tomography of the temporomandibular joint is compared with two established techniques, orthopantomography and lateral transcranio-oblique radiography. A high degree of concordance is demonstrated in the delineation of features of the joint, and circular tomography produces fewer radiographs than do the other two techniques in which these features are obscured. Circular tomography appears to be the best technique available at the present time for the study of the temporomandibular joint in patients with articular diseases.

Clinical experience with circular angiotomography.

Circular tomography has been used during cerebral angiography in patients with various pathological conditions in an effort to improve visualization of the brain and its blood vessels. Useful additional information was obtained in 7 of 24 patients studied; in one patient, the angiotornograrn showed a small metastasis that was not visible on the routine angiographic views. The blush over the cerebral hemispheres can be visualized, which should be useful in differentiating extra-axial and superficial intra-axial tumors and infarcts.

Polytome-encephalography in the investigation of pituitary tumours

Thirty-seven patients suffering from various types of pituitary tumours have been examined by pneumoencephalography combined with tomography using the Philips polytome. The technique described uses careful premedication by phenoperidine and haloperidol. Circular tomography in sagittal and coronal planes showed suprasellar anatomy in 39 out of 40 examinations. Fourteen patients had suprasellar extensions of tumour and three patients showed intrasellar air. The importance of accurate anatomical assessment of pituitary tumours is discussed. Suprasellar extension could not be predicted from the shape of the sella. Suprasellar extension may exist in the absence of visual field defects.

側頭骨断層撮影

The fine structural detail of the temporal bone is difficult to demonstrate in any direction by mean of ordinary roentgenography. Therefore, the tomography of the temporal bone has many advantages as postulated by Lemahieu (1952) for routine examination comparing to ordinary method. Curvilinear tomography, i.e, tomography with circular or similar symmetical movements, will give particularly good results in the examination of bone due to greater blurring of image other than focal plane and etc. Six projections of lateral, frontal, axial, Stenver's Owen's and Schuller's are selected for the precent study of the temporal bone by circular tomography. The best results were obtained in stenver's and axial projection for the three ossicles, in frontal projection for vestibule and internal auditory canal, in Owen's projection for canal, in Stenver's projection for pharyngo tympanic tube and in axial projection for temporal bone.

Polytome tomography

<h2>Summary</h2> Circular tomography has practical as well as theoretical advantages over linear tomography especially for examination of the skeleton. The Massiot-Philips Polytome has been found a satisfactory and convenient machine for performing both linear and circular tomography. It is easy to use, but a fully satisfactory examination can only be carried out if the radiography is either done by the radiologist himself or is done under very close supervision by the radiologist. In a large department the ability to choose a particular tomographic technique is a great asset, but just as tomography can never replace conventional radiography, the Polytome will not replace more simple tomographic attachments for routine daily use in most x-ray departments.