Three-dimensional Gradient-echo is Effective in Suppressing Radiofrequency Shielding by a Titanium Mesh

Assessing the radiofrequency shielding effect of titanium mesh on diffusion-weighted imaging: a comparative study of the twice-refocused spin-echo and Stejskal-Tanner sequences

This study compared twice-refocused spin-echo sequence (TRSE) and Stejskal-Tanner sequence (ST) to evaluate their respective effects on the image quality of magnetic resonance (MR) diffusion-weighted imaging in the presence of radiofrequency (RF) shielding effect of titanium mesh in cranioplasty. A 1.5-T MR scanner with a Head/Neck coil 20 channels and a phantom simulating the T2 and apparent diffusion coefficient (ADC) value of the human brain were used. Imaging was performed with and without titanium mesh placed on the phantom in TRSE and ST, and normalized absolute average deviation (NAAD), Dice similarity coefficient (DSC), and ADC values were calculated. The NAAD values were significantly lower for TRSE than for ST in the area below the titanium mesh, and the drop rates due to titanium mesh were 14.1% for TRSE and 9.8% for ST. The DSC values were significantly lower for TRSE than for ST. The ADC values were significantly higher for TRSE than for ST without titanium mesh. The ADC values showed no significant difference between TRSE and ST with titanium mesh. The ST had a lower RF shielding effect of titanium mesh than the TRSE.

Can magnetic resonance imaging after cranioplasty using titanium mesh detect brain tumors?

This study determined the dependence of the concentration and position of contrast-enhanced tumors on the radio frequency (RF)-shielding effect of titanium mesh using the contrast-to-noise ratio (CNR) in magnetic resonance imaging (MRI). A phantom was constructed by filling a plastic container with manganese chloride tetrahydrate and agar. Four cellophane cylindrical containers were arranged from the end of the plastic container, and the brain tumor model was filled with gadobutrol diluted with NaCl, with molarity values of 0.2-1.0 mmol/L. The titanium mesh board was set on the left side of the phantom. Images were acquired using a 1.5-T MRI as well as two-dimensional spin-echo (2D SE) and three-dimensional fast spoiled gradient echo (3D FSPGR) sequences. CNR was calculated using the signal intensity values of the tumor model, surrounding area of the brain model, and background noise. Furthermore, the fractional change in CNR was calculated using values of CNR with and without the mesh. Moreover, a profile of CNR was created. The fractional change in CNR decreased at the brain tumor positions present near the mesh and at a contrast medium concentration of approximately ≤ 0.5 mmol/L in 2D SE and ≤ 0.25 mmol/L in 3D FSPGR. According to the CNR profiles, directly under the mesh, almost all contrast concentrations in 2D SE was unrecognizable; however, at a concentration of ≥ 0.5 mmol/L in 3D FSPGR was recognizable.

[Features of modeling a polymer implant for closing a defect after decompressive craniotomy]

BACKGROUND

Individual polymer implants are widespread for bone reconstruction after decompressive craniectomy. Despite the availability of customized titanium products, various specialists and hospitals prefer polymer implants.

OBJECTIVE

To compare the methods of modeling and manufacturing the polymethylmethacrylate implants and identify the features affecting the quality of reconstruction.

MATERIAL AND METHODS

We analyzed 14 patients with extensive skull defects after installation of polymethyl methacrylate implants. Software used for modeling of individual implants by different specialists was compared.

RESULTS

Satisfactory reconstruction result was obtained in all cases. There were no infectious complications. The authors outlined certain important aspects for modeling of individual polymer products: local use of anatomical thickness of the implant, leaving safe spaces, prevention of temporal retraction, template-based resection before reconstruction.

CONCLUSION

To date, skull defect closure with polymeric materials remains relevant, and even has certain advantages over customized titanium products.

Echo-planar imaging is superior to fast spin-echo diffusion-weighted imaging for cranioplasty using titanium mesh in brain magnetic resonance imaging: a phantom study

This study aimed to compare the radiofrequency (RF) shielding effects of titanium mesh of echo-planar imaging (EPI) versus fast spin-echo (FSE) diffusion-weighted imaging (DWI) to establish a suitable sequence for patients who undergo cranioplasty and for whom titanium mesh was used in brain magnetic resonance imaging (MRI). A 1.5-T MRI scanner with clinical setting sequences was used. A phantom for the examination constructed using a sucrose solution in a plastic container was used to compare the signal attenuation (SA) ratio, area of RF shielding effect (Area), normalized absolute average deviation (NAAD), and apparent diffusion coefficient (ADC) between EPI and FSE-DWI. EPI provided significantly better SA ratio, Area, and NAAD (P < 0.01). When the number of slices increased, the RF shielding became more negative. There was no significant difference in the ADC. Regardless of the k-trajectory, EPI-DWI had a lower RF shielding effect than FSE-DWI in patients undergoing cranioplasty.