Fabio Tanzi

Relationship between a genetic predisposition to hypertension, blood pressure levels and pain sensitivity

INTRODUCTION The aim of this study was to determine whether the degree of blood pressure elevation and/or a genetic predisposition to hypertension have a major role in determining a reduced pain perception in hypertensives. The reasons underlying the relationship between blood pressure elevation and pain perception mechanisms are not completely understood. METHODS One hundred and four untreated hypertensive patients (65 subjects with and 39 without a positive parental history of hypertension) together with a control group of 42 subjects (20 normotensive offspring of normotensive parents, and 22 normotensive offspring of hypertensive parents) were submitted to standard blood pressure evaluation, 24-h blood pressure monitoring and dental pain perception evaluation. RESULTS Both pain threshold and tolerance were found to be higher in hypertensive than normotensive subjects (P < 0.0001 and P < 0.015, respectively). Positive significant correlations were found between both 24-h systolic and diastolic pressure and the pain perception variables. When a 2 x 2 ANOVA test was performed, factoring for the effects of both blood pressure status and family history of hypertension on pain sensitivity, a significant effect was revealed only for blood pressure status. Moreover, after controlling for blood pressure by a covariate analysis, no significant difference was found between the subjects with or without hypertensive parents as regards pain perception variables. CONCLUSIONS Pain sensitivity is correlated to blood pressure levels whereas the parental history of hypertension per se does not affect the pain perception pattern. Thus, the degree of blood pressure elevation, more than a genetic predisposition to hypertension may influence the mechanisms leading to hypalgesia in hypertension.

Dosimetric and image quality assessment of different acquisition protocols of a novel 64-slice CT scanner

Dose and image quality assessment in computed tomography (CT) are almost affected by the vast variety of CT scanners (axial CT, spiral CT, low-multislice CT (2-16), high-multislice CT (32-64)) and imaging protocols in use. Very poor information is at the moment available on 64 slices CT scanners. Aim of this work is to assess image quality related to patient dose indexes and to investigate the achievable dose reduction for a commercially available 64 slices CT scanner. CT dose indexes (weighted computed tomography dose index, CTDIw and Dose Length Product, DLP) were measured with a standard CT phantom for the main protocols in use (head, chest, abdomen and pelvis) and compared with the values displayed by the scanner itself. The differences were always below 7%. All the indexes were below the Diagnostic Reference Levels defined by the European Council Directive 97/42. Effective doses were measured for each protocol with thermoluminescent dosimeters inserted in an anthropomorphic Alderson Rando phantom and compared with the same values computed by the ImPACT CT Patient Dosimetry Calculator software code and corrected by a factor taking in account the number of slices (from 16 to 64). The differences were always below 25%. The effective doses range from 1.5 mSv (head) to 21.8 mSv (abdomen). The dose reduction system of the scanner was assessed comparing the effective dose measured for a standard phantom-man (a cylinder phantom, 32 cm in diameter) to the mean dose evaluated on 46 patients. The standard phantom was considered as no dose reduction reference. The dose reduction factor range from 16% to 78% (mean of 46%) for all protocols, from 29% to 78% (mean of 55%) for chest protocol, from 16% to 76% (mean of 42%) for abdomen protocol. The possibility of a further dose reduction was investigated measuring image quality (spatial resolution, contrast and noise) as a function of CTDIw. This curve shows a quite flat trend decreasing the dose approximately to 90% and a sharp fall below that value. A significant decrease in the effective dose to the patient, around 40%, was found; image quality analysis shows a further 10% dose reduction possibility.

A new sonographic method for the evaluation of skin permeability changes after irradiation with low-frequency ultrasound

The irradiation of the skin with low-frequency ultrasound (42 MHz) increases the skin permeability, allowing the US stimulated drug delivery (sonophoresis). The changes in the skin permeability is generally demonstrated with the measurement of corneometry and transepidermal water loss (TEWL). A novel ultrasound scanner with a 50 MHz probe was used for acquiring images of the skin (penetration depth few millimeters). The images show the different epidermal and dermis layers. A specially designed plexiglas basin containing an US transducer was used. Water was used as matching medium. The transducer was set to generate a 42 MHz continuous wave US beam with an intensity of 150 mW/cm2 for a chosen preset time. Ninety healthy volunteers were submitted to exposure of the back of the hand. The back of the hand of each person was scanned at 50 MHz before the irradiation and after 1, 15 and 60 minutes. A significant variation of the stratum corneum and the derma on the sonographic image was found. A particular software code was developed in order to quantify the amount of the variation in the image, using different parameters (entropy, energy, skewness, kurtosis, etc.) related to the pixel value in different regions of interest and to the cumulated profile along lines perpendicular to the skin surface. The variations in the parameters so defined were demonstrated to be statistically significant and with a sensibility much higher than corneometry and TEWL. This new approach allow to better understand the mechanism and quantify the changes in the skin permeability.

3D imaging of radioactivity in man measured with a whole body counter

In the Medical Physics Department of the University of Insubria, Varese, Italy, a whole body counter is in use, for clinical and radioprotection measurements. It consists of a scanning bed, four opposite (anterior-posterior and laterallateral) NaI(Tl) detectors and a shielding based on the shadow-shield principle. By moving the bed on which the patient lies in the supine position, the longitudinal profiles of the counts measured by each probe along the patient axis are obtained. Making the assumption that radioactivity is distributed in N voxel sources located in N selected positions in the patient, this distribution is calculated by solving an over-determined system of linear equations. The solution can be calculated using different methods. An iterative method and a regularization technique are presented. The algorithm proposed allows the evaluation of the distribution of the radioactivity in 3D in voxels with dimensions ranging from 15 to 20 mm, depending on the size of the patient. The 3D distribution of the radioactivity and the knowledge of the time of the intake allow the assessment of the effective dose.

Accuracy of mechanical index displayed on ultrasound scanners

The harmonic behavior of a ultrasound contrast agent (2nd generation) begins at a peak negative pressure of 10 kPa and finishes approximately at 60 kPa with the rupture of the contrast agents bubble. Moreover, increasing the power of the ultrasound pulse, the tissue begins to have a har-monic response too, affecting the imaging of the contrast agent. The survival of the bubbles is affected by different parameters; the most important is the intensity of the ultrasound beam which can be related to several index: peak negative pressure, acoustic intensity (Ispta) and the mechanical index (MI). Therefore with harmonic imaging it is important to use low power pulses with a good accuracy and reproducibility; in order to optimize this technique is necessary to find a good index of the probability of destruction of the bubbles. Most of the scanners use the display of the mechanical index as the parameter associated to the harmonic behavior of the contrast agent. A special phantom was realized in order to measure the MI of different probes of different scanners with a hydrophone. Aim of this study is to evaluate the accuracy of the MI displayed by different scanners and to verify its correlation with the others parameter related to the microbubbles persistence.

Fast treatment planning with IVUS imaging in intravascular brachytherapy

The planned target volume in intracoronary brachytherapy is the vessel wall. The success of the treatment is based on the need of delivering doses possibly not lower than 8 and not higher than 30 Gy. An automatic procedure in order to acquire intravascular ultrasound images of the whole volume to be irradiated is pointed out; a motor driven pullback device, with velocity of the catheter of 0.5 and 1 mm/s allows to acquire the entire target volume of the vessel with a number of slices normally ranging from 400 to 1600. A semiautomatic segmentation and classification of the different structures in each slice of the vessel is proposed. The segmentation and the classification of the structures allows the calculation of their volume; this is very useful in particular for plaque volume assessment in the follow-up of the patients. A 3D analyser tool was developed in order to visualize the walls and the lumen of the vessel. The knowledge, for each axial slice, of the position of the source (in the centre of the catheter) and the position of the target (vessel walls) allows the calculation of a set of source-target distances. Given a time of irradiation, and a type of source a dose volume histogram (DVH) describing the distribution of the doses in the whole target can be obtained. The whole procedure takes few minutes and then is compatible with a safe treatment of the patient, giving an important indication about the quality of the radiation treatment selected.