Proposed system for ultrafast computed tomography

Construction of a new ultrafast scanner system suitable for dynamic computed tomography is now under consideration, with development soon to begin. This system will be characterized by an electronically controlled X-ray generator with wide angle double diffraction, which will permit transverse axial images to be taken in times as short as 0.01 second.     

A film phantom for routine film dosimetry in the clinical environment

This paper describes a new film phantom we have designed that eliminates many of the problems found in phantoms used in film dosimetry. This phantom employs two sheets of solid water attached with nylon hinges and aligned with pins. It is made light-impermeable through the use of nylon hook-and-loop fasteners. This new design shows good agreement with ion-chamber measurements over the full depth of electron penetration.     

Gonadal thermoluminiscence dosimetry in cranial computed tomography with the EMI scanner

Summary A cranial computed tomographic examination (CT) consisting of four scans with the water bag equipped Mark I EMI scanner will expose the adult male gonads to a radiation dose of approximately 2 milliröntgen (mR).     

A protocol for the use of contrast enhancement in cranial computed tomography

There is some confusion regarding the indications for and methodology of the use of contrast material in cranial computed tomography. Some authors recommend a nonenhanced scan in all cases, followed by an enhanced scan if indicated by the symptoms or the appearance of the unenhanced scan. Others have questioned the value of the nonenhanced scan in patients with tumor. The authors offer a protocol for the use of contrast material. Possible tumor patients are scanned with contrast material alone; other patients are scanned either (a) without contrast material or (b) both with and without contrast material, depending upon the most likely clinical diagnosis.     

Preoperative use of computed tomography for foreign bodies

Computed tomography, with the possibility of density determination, makes possible the detection of foreign bodies that are not visible when using conventional techniques. The possibilities of localization are improved by the fact that tomograms are free of shadows and that distances can be measured exactly. These advantages provide important information in those cases in which surgical operation is planned.     

Comparison of dosimetry and image quality in computed and conventional tomography.

Comparison was made of tomograms of a phantom head and a normal adult cadaver head on GE CT/T, Delta 50, EMI 5005, and CGR Stratomatic units. Image quality was ranked as follows: First, GE CT/T 8800 system; second, EMI; third, GE CT/T 7800 and Delta. The GE CT/T 7800 imaged 3.7 line pairs at high contrast with an exposure to the head phantom of 2.5 R (6.5 X 10(-4) C kg-1). The EMI exposure level was 5 R (13 X 10(-4) C kg-1) in the fast mode and 12 R (31 X 10(-4) C kg-1) in the slow mode, while the Delta 50 exposure level was fixed at 2 R (5.2 X 10(-4) C kg-1). The GE CT/T 8800 could image 6.1 line pairs/cm in a high-contrast phantom with exposures as low as 100 mR (25.8 muC/kg) but a typical operating exposure would be about 1--2 R (2.58 -5.2 X 10 (-4) C kg-1). Dosimetry ranged from 1.1 to 5.5 R/scan section (2.8--14.2 x 10(-4) C kg-1) in the CT units but never increased by a factor of more than 2, irrespective of the number of sections scanned. In conventional tomography, however, exposure increased almost arithmetically with the number of contiguous sections scanned.     

Monte Carlo modeling of a conventional X-ray computed tomography scanner for gel dosimetry purposes

Our purpose in the current study was to model an X-ray CT scanner with the Monte Carlo (MC) method for gel dosimetry. In this study, a conventional CT scanner with one array detector was modeled with use of the MCNPX MC code. The MC calculated photon fluence in detector arrays was used for image reconstruction of a simple water phantom as well as polyacrylamide polymer gel (PAG) used for radiation therapy. Image reconstruction was performed with the filtered back-projection method with a Hann filter and the Spline interpolation method. Using MC results, we obtained the dose–response curve for images of irradiated gel at different absorbed doses. A spatial resolution of about 2 mm was found for our simulated MC model. The MC-based CT images of the PAG gel showed a reliable increase in the CT number with increasing absorbed dose for the studied gel. Also, our results showed that the current MC model of a CT scanner can be used for further studies on the parameters that influence the usability and reliability of results, such as the photon energy spectra and exposure techniques in X-ray CT gel dosimetry.     

High-resolution gel dosimetry using flat-panel detector cone-beam computed tomography: Preliminary study

This study compares the dose response of irradiated polymer gel with acrylic and styrofoam housing while applying multi-detector CT (MDCT) and cone-beam CT (CBCT). The dose response for MDCT and CBCT, while using an acrylic phantom is 1.34 and 0.67 ΔHU Gy^?1, respectively, and becomes 1.54 and 0.84 ΔHU Gy^?1 while using styrofoam, suggesting styrofoam is the better housing material. While the dose response of MDCT is better than that of CBCT, CBCT is yet a promising 3D dosimetry technique, given its potentially better spatial resolution and sensitive dose interpretation capability.     

Rationales for the use of intravenous contrast medium in computed tomography

There are currently many computed tomographic units with differing performance capabilities, resulting in confusion over protocols for contrast medium usage. Additionally, the development of the safer but more expensive low osmolar contrast agents has increased interest in evolving clearer indications for contrast medium usage in C.T. scanning. Rationales for the use of intravenous agents in C.T. scanning are proposed. These include the labelling of normal structures for anatomic clarification, the assessment of perfusion, the characterisation of a specific lesion, CT Angiography, demonstration of defects in the blood brain barrier and the phenomenon of neovascularity. The logical use of contrast agents should involve the deliberate invocation of one or more of these mechanisms coupled with the appropriate technique of administration.     

Comparison of image validity between cone beam computed tomography for dental use and multidetector row helical computed tomography

OBJECTIVES: To evaluate and compare the image validity of a cone beam CT machine for dental use (3DX) and the latest medical CT system, multidetector row helical CT (MDCT). METHODS: A dried right maxilla of an Asian adult was used as a phantom. It was cut from the zygomatic process towards the midline, parallel to the midline plane, into eight slices of 2 mm thickness. This phantom was imaged with the 3DX and MDCT machines. Images were evaluated by comparing them with one selected bone slice from the phantom. In this comparison, two types of MDCT images were used: one with the window level (WL) and window width (WW) suitable for observing teeth (MDCT tooth image), and the other appropriate for observing bone (MDCT bone image). Three dentists and one radiographer then used our reported subjective five-level scale to evaluate and compare images generated by the two systems in terms of validity. Cancellous bone as well as enamel, dentin, pulp cavity, periodontal ligament space, lamina dura and overall impression were evaluated. RESULTS: Statistically significant differences (P<0.05) were found for almost all observation items. Our subjective evaluation clarified that 3DX was superior to MDCT in terms of image validity. Few significant intra- or interevaluator errors were found. CONCLUSIONS: Our subjective evaluation of image validity clarified 3DX as being superior to MDCT. Taken together with the low skin dose we previously reported for 3DX, the results demonstrate 3DX to be beneficial for imaging diagnosis of hard tissues in the maxillofacial region.     

Radiochromic胶片剂量计

Radiochromic胶片剂量计可用来测量工业和医学领域中的电离辐射剂量。在医学领域,对这种剂量计的刻度方法、黑度剂量系统和应用原则还未做过详细的报道。现综述了医学领域中应用的剂量计的原理、胶片类型和材料组成、胶片特性、刻度方法、黑度扫描计系统及医学应用。