[Quantitative evaluation of low contrast detectability in a brain computed tomography: investigation for the effect of window width on recognition of hyperacute ischemic stroke].

In diagnostic brain computed tomography (CT) imaging of hyperacute ischemic stroke, the recognition of subtle lesions is difficult and may be missed. The aim of this study was to evaluate quantitatively the effect of the window width on low contrast detectability by using digital phantom images intended for detection of hyperacute ischemic stroke, and clinical CT images. We first derived the digital phantom images by subtracting the simulated signal data (intensity=1-3 hounsfield units (HU), diameter=10-30 mm) from the water phantom images at various mAs values. Observer studies were then performed under the various window widths at 20, 40, 60, and 80 HU by using the 30 digital phantom images and the 30 water phantom images. In addition, observer studies on brain CT images with 30 abnormal cases and 30 normal cases were performed under the window widths at 20 and 80 HU. Studies were also performed under the simultaneous display of the set of brain CT images on each window width. As a result of evaluation by receiver operating characteristic analysis, narrowing of the window width can improve the low contrast detectability in CT images with noticeable noise, and can decrease the variation in the interpretation skills between observers in clinical CT images. Moreover, the interpretation accuracy was improved by displaying simultaneously the clinical CT image set on window widths at 20 and 80 HU.

[New method of estimating effective energy for X-ray CT scanners].

Because the exposure dose in X-ray computed tomography examinations is sometimes difficult to determine, it is important to be able to estimate the dose for these examinations. The effective energy of the X-ray CT scanner is required to estimate exposure dose. Although the half-value-layer (HVL) method has been used to calculate effective energy, it is not an easy method. This paper proposes a technique by which effective energy can be easily calculated. Certain details were found to cause change in effective energy, and the ratio (inner-metal center-air ratio: IMCAR) between air dose and dose in fixing the metallic pipe in the isocenter of an X-ray CT scanner was necessary. The IMCAR from a different X-ray CT scanner was required, and, when effective energy was calculated, it showed an error of less than 0.7% for the half-value-layer method. The effect of this error on dose estimation was slight (0.4%). This technique is useful, because effective energy can easily be calculated with a high degree of accuracy.

[Histological changes in the rabbit kidney induced by transarterial injection of a hypertonic sodium chloride solution].

PURPOSE: To evaluate histological changes in normal renal tissue induced by the injection of a hypertonic liquid. MATERIALS AND METHODS: Transarterial injection was performed in 17 healthy rabbits at various rates of infusion and amounts of isotonic and hypertonic (7%) sodium chloride solutions. In group 1, 10 cc of isotonic sodium chloride solution was injected. In groups 2 and 3, 1-10 cc of hypertonic solution was injected at rates of 1.0 cc/sec and 0.05 cc/sec, respectively. After 20 minutes of hemostasis, renal weight measurements and histological examinations were performed. In three rabbits that received 10 cc of 7% sodium chloride, lung samples were also obtained, and histological changes were reviewed. RESULTS: There was no tissue injury in group 1, and in groups 2 and 3 the histological changes for infusions of 4-10 cc were greater than those of 1-3 cc. There was no vascular endothelial cell damage in any case. None of the histological changes were dose dependent, and the lungs showed no clear histological alterations. CONCLUSION: Higher doses of a hypertonic sodium chloride solution cause irreversible histological changes in the rabbit kidney.

[Comparative evaluation of absorbed dose and image quality in X-ray head CT scanning for hospital facilities in Gunma.].

Recently, the number of scans for X-ray computed tomography (CT) examinations has been rising due to the wide-spread use of multi-slice CT (MSCT) scanners. There is a concern that the total medical exposures will be increased by these examinations. In order to lower exposures, routine parameters for head CT examinations done at several hospitals in Gunma were investigated. In this study, the computed tomography dose index (CTDI(100, C)), noise, and low contrast resolution were measured. The CTDI(100, C) for all the hospitals exceeded the guideline (40mGy) suggested by the Japan Association of Radiological Technologists (JART). Low contrast resolution showed the coefficient of variation of +/-5% between hospitals. In conclusion, it was proposed that the technologists should reconsider the parameters of the head X-ray CTs, in cases where their output dose far exceeds the standard.

[Fundamental study of DSA images using gadolinium contrast agent].

Most contrast agents used in digital subtraction angiography (DSA) are non-ionic iodinated contrast agents, which can cause severe side effects in patients with contraindications for iodine or allergic reactions to iodine. Therefore, DSA examinations using carbon dioxide gas or examinations done by magnetic resonance imaging (MRI) and ultrasound (US) were carried out in these patients. However, none of these examinations provided images as clear as those of DSA with an iodinated contrast agent. We experienced DSA examination using a gadolinium contrast agent in a patient contraindicated for iodine. The patient had undergone MRI examination with a gadolinium contrast agent previously without side effects. The characteristics of gadolinium and the iodinated contrast agent were compared, and the DSA images obtained clinically using these media were also evaluated. The signal-to-noise (SN) ratio of the gadolinium contrast agent was the highest at tube voltages of 70 to 80 kilovolts and improved slightly when the image intensifier (I.I.) entrance dose was greater than 300 microR (77.4 nC/kg). The dilution ratios of five iodinated contrast agents showed the same S/N value as the undiluted gadolinium contrast agent. Clinically, the images obtained showed a slight decrease in contrast but provided the data necessary to make a diagnosis and made it possible to obtain IVR without any side effects. DSA examinations using a gadolinium contrast agent have some benefit with low risk and are thought to be useful for patients contraindicated for iodine.