Local diagnostic reference levels for intraoral dental radiography in the public hospitals of Cyprus.

PURPOSE: The purpose of this study was to determine local DRLs for children and adults undergoing intraoral dental examinations at the intraoral radiology units of the public hospitals in Cyprus. METHODS: Measurements were made on all the twenty intraoral X-ray units of the public hospitals in Cyprus with the intention to establish the local DRLs for all the possible intraoral X-ray examinations for children and adults. All units are film based. The measurements were made by a Dose Area Product (DAP) meter (GAMMEX RMI 841-RD) placed at the surface of the dental unit's X-ray shaping cone (FSD 20cm). A diagnostic radiology dosimeter (Dosimax Plus A) was also placed at an FSD of 100cm to compare the dose reading between the two dosimeters. RESULTS: DRLs were established at the 3rd quartile for 7 exposure settings corresponding to 12 types of teeth (Adult and children mandibular and maxillary incisor, premolar and molar) with values of 197, 163, 128, 102, 81, 65 and 49mGycm-2 and 7.23, 5.94, 4.75, 3.68, 3.10, 2.41 and 1.88mGy for benchmark nominal exposure times of 1000, 800, 640, 500, 400, 320 and 250ms respectively, at a nominal exposure voltage of 70kVp. CONCLUSIONS: The local DRLs of the present study compare well with other similar published DRLs.

Indicator dilution models for the quantification of microvascular blood flow with bolus administration of ultrasound contrast agents.

Indicator dilution methods have a long history in the quantification of both macro- and microvascular blood flow in many clinical applications. Various models have been employed in the past to isolate the primary pass of an indicator after an intravenous bolus injection. The use of indicator dilution techniques allows for the estimation of hemodynamic parameters of a tumor or organ and thus may lead to useful diagnostic and therapy monitoring information. In this paper, we review and discuss the properties of the lognormal function, the gamma variate function, the diffusion with drift models, and the lagged normal function, which have been used to model indicator dilution curves in different fields of medicine. We fit these models to contrast-enhanced ultrasound time-intensity curves from liver metastases and the ovine corpora lutea. We evaluate the models' performance on the image data and compare their predictions for hemodynamic-related parameters such as the area under the curve, the mean transit time, the full-width at half-maximum, the time to the peak intensity, and wash-in time. The models that best fit the experimental data are the lognormal function and the diffusion with drift.

Investigation of the relationship of nonlinear backscattered ultrasound intensity with microbubble concentration at low MI.

The aim of this study was to measure the relationship of image intensity with contrast agent concentration. In vitro experiments were performed with a flow phantom and a sulphur hexafluoride filled microbubble contrast agent (SonoVue) at different concentrations (0.004 per thousand to 4 per thousand) covering the range commonly encountered in clinical practice. The concentration of microbubbles in the contrast agent solutions was confirmed optically. Images were collected with a diagnostic ultrasound system (iU22, Phillips Medical Systems, Bothell, WA, USA) and with a nonlinear imaging technique (power modulation) at low mechanical index (MI=0.05) to avoid bubble destruction. The mean intensity within a region of interest was measured to produce time-intensity curves from linearized (absolute scale) data. The relationship of linearized image intensity to contrast agent concentration was found to be linear up to 1 per thousand and reached a plateau at approximately 2 per thousand. To operate in the linear range of the intensity-concentration relationship the contrast agent dose should be adjusted to avoid those high values in vivo and the highest dynamic range of the ultrasound system should be used to avoid unnecessary signal saturation.

Quantification of tumor microvascularity with respiratory gated contrast enhanced ultrasound for monitoring therapy.

The aim of this feasibility study was to evaluate the response to cytotoxic and antiangiogenic treatment of colorectal liver metastasis using respiratory gated contrast enhanced ultrasonography. Seven patients were monitored with contrast enhanced ultrasound. Sulfur hexafluoride filled microbubbles (SonoVue; Bracco S.P.A., Milan, Italy) were used as contrast agent and the scans were performed with a nonlinear imaging technique (power modulation) at low transmit power (MI=0.06). The mean image intensity in the metastatic lesion and in the normal liver parenchyma were measured as a function of time and time-intensity curves from linearized image data were formed. A novel respiratory gating technique was utilized to minimize the effects of respiratory motion on the images. A reference position of the diaphragm (or other echogenic interface) was selected and all frames where the diaphragm deviated from that position were rejected. The wash-in time (start of enhancement to peak) of metastasis and adjacent normal liver parenchyma was measured from time-intensity curves. The ratio of wash-in time of the lesion to that of the normal parenchyma (WITR) was used to compare the perfusion rate. In a reproducibility study (five patients), the average deviation of WITR was found to be 9%. There was an increase in the WITR for patients responding to treatment (mean WITR increase of 17% after first dose of treatment and 75% at the end of the therapy). In four out of five patients (80%) responding to therapy WITR predicted their response from the first treatment. All six patients that responded to therapy by the end of the therapy cycle (6-9 doses) were correctly predicted by using WITR. The WITR may be a new surrogate marker indicative of early tumor response for colorectal cancer patients undergoing cytotoxic and antiangiogenic therapy. (E-mail: maverk@ucy.ac.cy).