Agarose Gel Phantoms Research Articles

Magnetic resonance imaging of agarose gel phantom for assessment of three-dimensional dose distribution in linac radiosurgery

An agarose gel phantom is used to evaluate the spatial distribution of the dose delivered by a linac radiosurgery device. Dependence of the absorbed dose on the T1 relaxation time is checked. T1 magnetic resonance images show the close correspondence between the actual absorbed dose distribution and the dose distribution expected by the treatment planning.

Three-Dimensional Triple-Quantum-Filtered Imaging of 0.012 and 0.024 M Sodium-23 Using Short Repetition Times

The gradient-selected triple-quantum-filtered (GS3Q) esperiment, developed to improve the contrast in NMR imaging of sodium-23 (23Na) in the human brain, is limited by low signal-to-noise ratio (SNR). We have analyzed the GS3Q experiment and show here that the improvement in GS3Q-filtered 32Na SNR as the repetition time (TR) decreases is accompanied by the appearance of spurious one-quantum (1Q) 23Na signals. An improved filter with better suppression of spurious 1Q 23Na signals is obtained by adding a preparatory crusher gradient and two-step phase cycling to a conventional GS3Q filter. The relative contributions of 3Q coherence and spurious 1Q coherences to the conventional and modified-GS3Q-filtered signals are calculated, providing a measure of the effectiveness of each GS3Q filter. The filters were implemented on a 2.35 T medium-bore spectrometer and their predicted properties verified. SNR measurements from GS3Q-filtered three-dimensional images of an agarose gel phantom indicate that 0.012 M23Na images in the human brain can be acquired with 8 cm3 voxels and SNR of 10 in 30 minutes at 2.35 T, assuming similar relaxation times.

Nickel-Doped Agarose Gel Phantoms in MR Imaging

A method for the production of a tissue-mimicking phantom material for MR imaging is described. The material consists of a nickel-doped agarose gel. The T1 and T2 values of the gel can be varied independently by changing the relative amounts of nickel and agarose. Practically any T1 and T2 combination of clinical interest can be obtained. The long-term stability was studied and found to be good. The relaxation times were estimated using an MR analyzer. The accuracy and the reproducibility of these measurements were evaluated and found to be reassuring. Gel phantoms were also scanned in an MR unit. The signal strength of an inversion recovery sequence was evaluated using the gel phantoms in order to verify their usefulness. These measurements were compared to theory with good agreement. Furthermore, tissue-equivalent phantoms were made. Gels resembling gray matter, white matter, and CSF were scanned. Comparisons with clinical in vivo scans, as well as calculated levels were made. It is anticipated that the gel phantoms described here will be useful in quality assurance as well as in pulse sequence optimization.

Nickel-Doped Agarose Gel Phantoms in MR Imaging

A method for the production of a tissue-mimicking phantom material for MR imaging is described. The material consists of a nickel-doped agarose gel. The T1 and T2 values of the gel can be varied independently by changing the relative amounts of nickel and agarose. Practically any T1 and T2 combination of clinical interest can be obtained. The long-term stability was studied and found to be good. The relaxation times were estimated using an MR analyzer. The accuracy and the reproducibility of these measurements were evaluated and found to be reassuring. Gel phantoms were also scanned in an MR unit. The signal strength of an inversion recovery sequence was evaluated using the gel phantoms in order to verify their usefulness. These measurements were compared to theory with good agreement. Furthermore, tissue-equivalent phantoms were made. Gels resembling gray matter, white matter, and CSF were scanned. Comparisons with clinical in vivo scans, as well as calculated levels were made. It is anticipated that the gel phantoms described here will be useful in quality assurance as well as in pulse sequence optimization.