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.
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.
We have developed a software, which allows to do non conventional percent quantitative analysis on scintigraphic polar map obtained from conventional processing of gated-SPECT acquisitions. Polar maps are 8 bit images of perfusion, motion, ejection fraction (EF) and thickening, of the heart.
The software is written in Matlab, analyses the whole polar map and four ROIs corresponding to the theoretical LAD, LCX, RCA territories (perfused by these arteries) and extra-ROIs region. An intensity segmentation is performed. The area corresponding to pixels lower and higher than a varying cut-off are calculated on the whole image and for each ROI. The software calculates an intensity-area histogram, which is the analogous of the Dose-Volume Histogram used in radiation therapy: in this case, the histogram has the meaning of a Perfusion- or a Motion-Volume histogram. Then, the software applies the Lyman-Wolbarst algorithm, to calculate the area equivalent histogram reduction (e.g. the perfused area in the hypothesis that all pixels are perfused at 100%.). The makes a direct comparison between two different polar maps by choice. The comparison between the numerical quantification of motion and perfusion maps, allows the physicians to get a clinical evaluation of the stunned myocardium.
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.
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 agent's 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.
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.