A new tissue-equivalent MRI phantom based on carrageenan gel was developed. Carrageenan gel is an ideal solidifying agent for making large, strong phantoms in a wide variety of shapes. GdCl 3 was added as a T 1 modifier and agarose as a T 2 modifier. The relaxation times of a very large number of samples were estimated using 1.5-T clinical MRI equipment. The developed phantom was found to have a T 1 value of 202-1904 ms and a T 2 value of 38 -423 ms when the GdCl 3 concentration was varied from 0 -140 mol/kg and the agarose concentration was varied from 0 -1.6% in a carrageenan concentration that was fixed at 3%. The range of measured relaxation times covered those of all types of human tissue. Empirical formulas linking the relaxation time with the concentration of the modifier were established to enable the accurate and easy calculation of the modifier concentration needed to achieve the required relaxation times. This enables the creation of a phantom having an arbitrary combination of MRI phantoms are useful for calibrating and checking imaging equipment, developing new systems and pulse sequences, and training MRI operators. To be useful in these roles, the material used to make MRI phantoms should 1) have relaxation times similar to those of human tissue; 2) provide uniform relaxation times throughout the phantom itself; 3) be strong enough to enable the fabrication of a "torso" without the use of physical reinforcements; 4) allow the production of phantoms in the shapes and sizes of human organs; 5) be easy to handle; and, 6) remain chemically and physically stable over extended periods.There have been several attempts to create solid materials for MRI phantoms. Former candidates have included agarose (1-5), agar (6,7), polyvinyl alcohol (PVA) (8), gelatin (9,10), TX-150 (11), TX-151 (12), and polyacrylamide (13). These gel phantoms usually contained additives such as paramagnetic ions to control the T 1 relaxation times. The most versatile phantoms are probably the paramagnetically doped gels that are based on agarose (1-5) or agar (6,7). In these systems, the T 1 relaxation times can be easily modulated by varying the concentrations of the paramagnetic ions, whereas the T 2 relaxation times are primarily a function of the gelling agent concentration. In a phantom that is based on polyacrylamide gel (13), both the T 1 and T 2 relaxation times can be modulated simultaneously by varying the concentration of the gel without the paramagnetic ions. These phantoms are easy to prepare and can be made with a wide range of T 1 and T 2 relaxation times including those of human tissue. To create a phantom with a human-like T 2 relaxation time of about 40 -150 ms, however, the concentration of agar, agarose, and polyacrylamide must be about 1.5-3.0, 0.8 -4.0, and 17-30%, respectively. To create a phantom having a long T 2 relaxation time, the concentration would be so low that the gel would not solidify sufficiently. A PVA gel phantom can offer the appropriate physical characteristics because it is as hard as the st...

We previously developed two new MRI phantoms (called the CAG phantom and the CAGN phantom), with T1 and T2 relaxation times equivalent to those of any human tissue at 1.5 T. The conductivity of the CAGN phantom is equivalent to that of most types of human tissue in the frequency range of 1 to 130 MHz. In this paper, the relaxation times of human tissues are summarized, and the composition of the corresponding phantoms are provided in table form. The ingredients of these phantoms are carrageenan as the gelling agent, GdCl3 as a T1 modifier, agarose as a T2 modifier, NaCl (CAGN phantom only) as a conductivity modifier, NaN3 as an antiseptic, and distilled water. The phantoms have T1 values of 202-1904 ms and T2 values of 38-423 ms when the concentrations of GdCl3 and agarose are varied from 0-140 micromol/kg, and 0%-1.6%, respectively, and the CAGN phantom has a conductivity of 0.27-1.26 S/m when the NaCl concentration is varied from 0%-0.7%. These phantoms have sufficient strength to replicate a torso without the use of reinforcing agents, and can be cut by a knife into any shape. We anticipate the CAGN phantom to be highly useful and practical for MRI and hyperthermia-related research.

An increased systemic production of oxygen-free radicals by activated inflammatory cells is thought to be involved in the pathophysiology of asthma. The aim of this study is to evaluate the clinical effects of radon and thermal therapy on asthma in relation to antioxidant enzymes and lipid peroxide. Radon and thermal therapy were performed once a week. All subjects went to a hot bathroom with a high concentration of radon, and nasal inhalation of vapor from a hot spring was performed for 40 min once a day under conditions of high humidity. The room temperature was 48 degrees C; the room radon concentration was 2,080 Bq/m3. Blood samples were collected at 2 h, 14, and 28 days after the first therapy. A blood sample also was collected before the first therapy (at body temperature and background radon level) to be used as the control. The forced expiratory volume in one second (%FEV1) was significantly increased 28 days after the first therapy. On day 28, the catalase (CAT) activity was significantly increased in comparison with the control. The superoxide dismutase (SOD) activity was significantly increased compared to the control after first inhalation. On days 14 and 28, the lipid peroxide level was significantly decreased in comparison with the control. In conclusion, the present pilot study has shown that radon and thermal therapy improved the pulmonary function of asthmatics by increasing the reduced activities of antioxidant enzymes.

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The catalase activities in blood and organs of the acatalasemic (C3H/AnLCs(b)Cs(b)) mouse of C3H strain are lower than those of the normal (C3H/AnLCs (a)Cs(a)) mouse. We examined the effects of prior low-dose (0.5 Gy) X-ray irradiation, which reduced the oxidative damage under carbon tetrachloride-induced hepatopathy in the acatalasemic or normal mice. The acatalasemic mice showed a significantly lower catalase activity and a significantly higher glutathione peroxidase activity compared with those in the normal mice. Moreover, low-dose irradiation increased the catalase activity in the acatalasemic mouse liver to a level similar to that of the normal mouse liver. Pathological examinations and analyses of blood glutamic oxaloacetic and glutamic pyruvic transaminase activity and lipid peroxide levels showed that carbon tetrachloride induced hepatopathy was inhibited by low-dose irradiation. These findings may indicate that the free radical reaction induced by the lack of catalase and the administration of carbon tetrachloride is more properly neutralized by high glutathione peroxidase activity and low-dose irradiation in the acatalasemic mouse liver.

This is the first report to provide radiation doses, arising from inhalation of radon itself, in mice and rats. To quantify absorbed doses to organs and tissues in mice, rats, and humans, we computed the behavior of inhaled radon in their bodies on the basis of a physiologically based pharmacokinetic (PBPK) model. It was assumed that radon dissolved in blood entering the gas exchange compartment is transported to any tissue by the blood circulation to be instantaneously distributed according to a tissue/blood partition coefficient. The calculated concentrations of radon in the adipose tissue and red bone marrow following its inhalation were much higher than those in the others, because of the higher partition coefficients. Compared with a previous experimental data for rats and model calculation for humans, the present calculation was proved to be valid. Absorbed dose rates to organs and tissues were estimated to be within the range of 0.04-1.4 nGy (Bq m À3 ) À1 day À1 for all the species. Although the dose rates are not so high, it may be better to pay attention to the dose to the red bone marrow from the perspective of radiation protection. For more accurate dose assessment, it is necessary to update tissue/blood partition coefficients of radon that strongly govern the result of the PBPK modeling.

The radioactive and thermal effects of radon hot spring were biochemically compared under a sauna room or hot spring conditions with a similar chemical component, using the parameters that are closely involved in the clinic for radon therapy. The results showed that the radon and thermal therapy enhanced the antioxidation functions, such as the activities of superoxide dismutase (SOD) and catalase, which inhibit lipid peroxidation and total cholesterol produced in the body. Moreover the therapy enhanced concanavalin A (ConA)-induced mitogen response and increased the percentage of CD4 positive cells, which is the marker of helper T cells, and decreased the percentage of CD8 positive cells, which is the common marker of killer T cells and suppressor T cells, in the white blood cell differentiation antigen (CD8/CD4) assay. Furthermore, the therapy increased the levels of alpha atrial natriuretic polypeptide (alpha ANP), beta endorphin, adrenocorticotropic hormone (ACTH), insulin and glucose-6-phosphate dehydrogenase (G-6-PDH), and it decreased the vasopression level. The results were on the whole larger in the radon group than in the thermal group. The findings suggest that radon therapy contributes more to the prevention of life-style-related diseases related to peroxidation reactions and immune suppression than to thermal therapy. Moreover, these indicate what may be a part of the mechanism for the alleviation of hypertension, osteoarthritis (pain), and diabetes mellitus brought about more by radon therapy than by thermal therapy.

The authors developed a phantom, designated as the CAGN phantom, compatible for MRI and hyperthermia that is useful in the fundamental studies of non-invasive MR thermometry. The ingredients of this phantom are carrageenan, GdCl3 as a T1 modifier, agarose as a T2 modifier, NaCl as a conductivity modifier, NaN3 as an antiseptic and distilled water. Another phantom that was developed, the CAG phantom, has relaxation times that are adjustable to those of any human tissue. To use this phantom for electromagnetic heating, NaCl was added to change the conductivity of the phantom and clarified the relationship between the conductivity and NaCl concentration. This study examined the relationship between relaxation times and NaCl concentration of the CAGN phantom. The results showed that both T1 and T2 values were affected by NaCl and the experimental results led to the empirical formulae expressing the relationship between the relaxation rates (1/T1, 1/T2) and the concentrations of GdCl3, agarose and NaCl. The appropriate concentrations of T1 and T2 modifiers were calculated from these empirical formulae when making a specified phantom that has the required relaxation times and NaCl concentration.