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 estimation of cell kinetic parameters was made by simultaneous flow cytometric measurements of DNA and bromodeoxyuridine (BrdUrd) contents of cells. The procedure described in this paper involves the incorporation of BrdUrd by S phase cells, labeling the BrdUrd with an indirect immunofluorescent technique using a monoclonal anti-RrdUrd antibody, and staining DNA with propidium iodide (PI). The amount of incorporated RrdUrd in HeLa cells was proportional to that of synthesized DNA through S phase. For all cell lines examined, the pattern of BrdUrd incorporation was essentially the same and the rate of DNA synthesis during S phase was not constant. The bivariate BrdUrd/DNA distributions showed a horse-shoe pattern, maximum in the mid S phase and minimum in the early and late S phases. Furthermore, the durations of cell cycle Cl'c) and S phase CTs) were estimated from a FLSm (fraction of labeled cells in mid S phase) curve that was generated by plotting the percentage of BrdUrd pulselabeled cells in a narrow window defined in the mid S phase of the DNA histogram. The values of these parameters in NIH 3T3, HeLa S3, and HL-60 cells were in good accordance with the reported data. This FCM method using the monoclonal anti-BrdUrd antibody allows rapid determination of both cell cycle compartments and also Ts and Tc without the use of radioactive DNA precursors.Key terms: Dual-parameter FCM analysis, DNA synthesis rate, cell kinetics With the advent of flow cytometry (FCM), rapid quantitation of cellular DNA content has become feasible, and this technique has been increasingly employed in studying cell kinetics. Many mathematical methods have been reported in an attempt to resolve DNA distributions into the three compartments of cell cycle, G1, S, and G2M. For the more reliable estimation of cell kinetic parameters, knowledge of the DNA synthesis rate is a necessary and biologically interesting subject (2,3,13,14). However, the pattern of the DNA synthesis rate throughout the S phase is still a matter of controversy.Recently, a monoclonal antibody against bromodeoxyuridine (BrdUrd), which is a pyrimidine analogue of thymidine, was developed (11,lZ) Our attempt is to use a monoclonal anti-BrdUrd antibody for the rapid estimation of the durations of cell cycle (Tc) and S phase (Ts). These parameters can be estimated by the FLSm (fraction of labeled cells in the mid S phase) curve that is provided by plotting labeling indices in a narrow window against the time after BrdUrd pulse-labeling. Although the BrdUdDNA FCM Presented at the Kansai Flow Cytometry I11 Conference, Osaka, April 1985.
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