High energy probe for detecting lymph node metastases with 18F-FDG in patients with head and neck cancer.

AIM: of this study was to validate a newly developed high energy probe (positron emission probe, PEP) optimised for localising PET tracers in vivo. PATIENTS AND METHODS: Physical investigations included determination of full width at half maximum (FWHM) values at a distance of 1 cm and angular resolution using different point sources. Values obtained with the new probe were compared to those of a conventional gamma probe (CGP). Additionally, PET studies were performed in 36 patients (6 women, 30 men) with proven head and neck cancer and suspected lymph node metastases (Axis, Marconi/Philips) after administering 250-320 MBq (18)F-FDG. Subsequent to PET investigations (18)F-FDG uptake in cervical regions was measured using the PEP. PEP investigations were carried out bilaterally in 5 lymph node (LN) levels (Robbins' classification of the neck). Results of probe studies were correlated with visual and semiquantitative PET evaluations, US and histological findings. RESULTS: FWHM of the new probe was 7 mm (CGP 22 mm) at 662 keV ((137)Cs) and angular resolution resulted in 8 degrees (CGP 60 degrees ). In 29 out of 36 patients LN metastases were suspected due to ultrasound investigations. After neck dissection, histology confirmed LN metastases in 21 patients. Sensitivity (sens.) of US amounted to 95% and specificity to 40%. In 18/21 patients LN metastases were detected by PET (sens. 86%). PET scans failed to diagnose the LN status correctly in 6/36 patients (accuracy 83%). Employing the PEP probe in 20/21 patients LN metastases were identified (sens. 95%), and LN status was determined accurately in 29/36 patients (accuracy 81%). Tumour/background ratios of PEP measurement and results of semiquantitative PET analyses were comparable. CONCLUSIONS: PEP measurement is a promising method for preoperative planning of the extent of neck dissection in patients with head and neck cancer and further for radioguided localising PET tracer accumulation during surgery.

Radiofrequency dielectric properties of animal tissues as a function of time following death.

The dielectric properties of three bovine tissues, liver, kidney and spleen, as a function of time following death, were measured in the frequency range from 20 kHz to 100 MHz using an automatic network analyser and an end-of-the-line sensor. The dielectric constant of kidney and spleen decreases as a function of time following death, particularly at frequencies below 1 MHz. However, all tissues measured show a characteristic increase in the frequency-independent ionic conductivity. This is believed to reflect changes in the conductivity of the extracellular region of tissues after death. The dielectric parameters, i.e. the static dielectric constant, the relaxation time and the coefficient of the relaxation time distribution, obtained by a curve-fitting process, do not change within the first 10 h following death in the case of liver, whereas early changes occur for both kidney and spleen. High initial values of the static dielectric constant for these tissues decrease significantly within a few hours following death. Similarly, the relaxation time which is relatively long for kidney and spleen, as compared with liver, decreases with time. Our data compare favourably with those reported by several investigators for similar tissues in other species (dog, cat, swine and cattle).

Dielectric properties of human B and T lymphocytes at frequencies from 20 kHz to 100 MHz.

Dielectric properties of the human B and T lymphocytes were measured. The experiments were performed at frequencies from 20 kHz to 100 MHz for different cell concentrations at 24 and 37 degrees C. An end of the line capacitive sensor and a computer-controlled automatic network analyser were utilised. Cole-Cole dielectric parameters were determined by curve fitting using a computer program. Specific membrane capacitances (Cm) were calculated from the experimental data (assuming a membrane charging mechanism) to be 0.77 and 2.89 microF cm-2 for the T and B lymphocytes, respectively. The fitted relaxation time is located in the centre of the calculated relaxation time distribution spectrum for the B lymphocytes, while it is shifted towards higher values of the relaxation time equivalent to the larger cells for the T lymphocytes. The distribution of the relaxation times was estimated on the basis of the Maxwell-Wagner dispersion reflecting membrane-charging processes.

In vitro dielectric properties of human tissues at radiofrequencies.

In vitro permittivity measurements of excised human liver, spleen, kidney and cardiac muscle at frequencies from 10 kHz to 100 MHz are described. An end-of-the-line capacitive sensor and a computer-controlled network analyser HP 3577 were employed. The results were compared with human data reported by other investigators as well as with the animal (cat) data obtained earlier in this laboratory. It was found that the conductivity of most of the human tissues tested was significantly higher than that of the animal tissues for the test frequencies. The dielectric constants for human kidney and spleen are higher than the corresponding animal (cat) tissues at frequencies from 10 kHz to approximately 1 MHz and at around 100 MHz. However, the values for liver do not differ significantly between the two species in the same frequency range.

In vivo and in vitro dielectric properties of feline tissues at low radiofrequencies.

The dielectric constant and conductivity of muscle, liver, spleen and kidney of cats in vivo and in situ immediately following the animal's death were measured at frequencies from 10 kHz to 100 MHz. A novel multi-ring capacitive sensor and a computer-controlled automatic network analyser (ANA) were employed. The results were compared with the data available from literature for the same species in the frequency range between 10 and 100 MHz. It was found that at frequencies from 10 to 100 kHz the in vitro dielectric constant for all tissues except spleen was smaller than the in vivo one. In contrast, in the range from 1 to 100 MHz the in vitro dielectric constant was larger than the in vivo one. At intermediate frequencies from 0.1 to 1 MHz both the dielectric constant in vivo and in vitro were the same within the experimental uncertainty. The dielectric constant of the spleen in vivo was quite similar to that in vitro. The in vivo conductivity of all tissues appeared to be higher than in vitro from 10 kHz to 10 MHz, while at frequencies above 10 MHz the two conductivities were within the experimental uncertainty.

A simple method for the determination of DNA molecular weight distribution.

A method is described for the molecular weight distribution of DNA which is determined from sedimentation-velocity analysis. Knowing the distribution of sedimentation coefficients for a single DNA concentration it is possible to extrapolate such a distribution to infinite dilution of the solute in a simple way. Two versions (using two or three terms of a series) of extrapolating equations are considered and discussed in detail. The sedimentation coefficients distribution calculated from these equations differs only insignificantly with that obtained in a conventional way.

Utilization of a commercial prostate brachytherapy planning system for 3D treatment planning of ophthalmic tumors.

The 3D brachytherapy transperineal ultrasound implant (B3DTUI) program by the Multimedia Medical System has been adopted for eye plaque treatment planning. The post op CT digitization option was selected to enter the actual seed coordinates present in the eye plaque. Although the B3DTUI algorithm is designated to calculate a permanent dose values, the described procedure allows determination of the dose distribution as the dose rate values. The dose computation program utilizes updated source quantities recommended by the AAPM TG-43 formalism, such as air kerma strength, dose rate constant, radial dose function, and anisortopy factor function. As a result, more accurate dose distribution in the target is obtained than by using traditional dose computation formalism.

Heating characteristics of the TRIPAS hyperthermia system for deep seated malignancy.

A deep heating hyperthermia device TRIPAS (a triapplicator system) consisting of three independent, dielectrically loaded horn applicators operating in phase at 300 MHz was investigated. The heating characteristics produced by this hyperthermia system were analyzed by means of thermochromic liquid-crystal cards and a modified CDRH (Center for Devices and Regulatory Health) elliptical phantom. Both homogenous and inhomogeneous phantoms were used, simulating high and low permittivity tissues (muscle and lung). These equivalent tissues were made of polyacrylamide gel. The semiquantitative heating pattern analysis showed a central heating of 1/3 of maximum heating at a depth of 10 cm in both homogenous (muscle) and heterogenous (muscle/fat) phantoms. Also more uniform temperature/SAR distributions were generated in muscle equivalent material than those in lung.

[Latent iron-binding capacity of normal serum proteins by means of Fe-59]. / Badania utajonej zdolnosci wiazania zelaza przez bialka prawidlowej surowicy krwi przy pomocy 59Fe.

Experimental investigations were carried out for confirming the possibility of saturation of the basic serum components with exogenous iron (not only transferin). In gel chromatography, paper electrophoresis and acetate cellulose electrophoresis it was demonstrated that the latent capacity for iron saturation is a feature of not only transferrin belonging to beta1 globulins, but also to some extent of albumins and alpha-globulins. Iron distribution was studied after 59Fe administration. The iron-binding capacity of alpha-globulins was many times higher than that of albumins.

Simulated biological materials for electromagnetic radiation absorption studies.

For the study of electromagnetic dosimetry and hyperthermia, it is necessary to simulate human biological materials. This can be done by chemical mixtures that are described in this paper. Formulas are presented for simulating bone, lung, brain, and muscle tissue in the frequency range of 100 MHz to 1 GHz. By using these preparations a realistic equivalent to the human body can be constructed.

Use of the loss-tangent function in dielectric spectroscopy.

A new method for finding the dielectric parameters of biological substances is presented. The method makes use of the loss-tangent as a function of frequency to identify the dominating relaxation process. The method was tested for a few cell suspensions (blood and lymphocytes) and two tissues (liver and spleen). The obtained parameters agree well with those calculated from Maxwell-Wagner theory (beta dispersion).

Postmortem changes of the dielectric properties of bovine brain tissues at low radiofrequencies.

The dielectric properties of the bovine brain grey and white matter in the frequency range from 20 kHz to 100 MHz were measured at different times following animal death. Changes in the dielectric parameters versus time are interpreted in terms of the reduction of the cell volume fraction that results from either cell disintegration or cell size reduction. Good agreement between the computer fitted parameters and the values calculated from the Maxwell-Wagner model of the static dielectric constants was found. At frequencies above 1 MHz the changes of the dielectric properties are less pronounced, confirming earlier observations made by other investigators for different species.

Utilization of a multilayer polyacrylamide phantom for evaluation of hyperthermia applicators.

A muscle-stimulating material made of polyacrylamide gel (PAG) for testing various kinds of hyperthermia applicators was investigated. The permittivity and conductivity dispersion of PAG, as well as an internal wavelength and penetration depth, were in good agreement with those of actual muscle at frequencies between 500 MHz and 3 GHz. A single formula for PAG covering three ISM bands, most commonly used for hyperthermia, 433, 915 and 2450 MHz, is presented. The physical properties of the PAG phantom allow any desired form or shape to be moulded, including shapes conforming to the actual geometry of an interstitial or intracavitary applicator. Utilization of a multilayer phantom makes possible the generation of experimental three-dimensional specific absorption rate (SAR) distributions composed from several two-dimensional SAR images at different depths or radial distances from the applicator. Spatial resolution of 1 mm can be achieved. The two-dimensional SAR distributions at different depth values for commercial superficial applicator, an interstitial antenna and a new oesophageal applicator are presented.

Dielectric properties of mouse MCA1 fibrosarcoma at different stages of development.

The in vitro bulk electrical properties of MCA1 fibrosarcoma induced in C57B1/6 male mice were measured at frequencies of 10 kHz to 100 MHz, with some tissues measured to 2 GHz. The properties of normal surrounding tissue also were measured. A comparison of the dielectric properties between three different stages of tumor development as well as that between various locations within the tumor is reported. Statistical analysis of the experimental results revealed statistically significant differences in the dielectric constant and conductivity of the tumor tissues at various stages of development as measured at frequencies below 10 MHz. Conductivity values at different stages also differ at a frequency of 100 MHz. At other frequencies these differences were found to be statistically insignificant.