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Use of a radio frequency shield during 1.5 and 3.0 Tesla magnetic resonance imaging: experimental evaluation.

Favazza CP, King DM, Edmonson HA, Felmlee JP, Rossman PJ, Hangiandreou NJ, Watson RE, Gorny KR - Med Devices (Auckl) (2014)

Bottom Line: Attenuation, by as much as 35 dB, of RF field power was found inside the RF shield.These results were supported by temperature measurements of metallic leads placed inside the shield, in which no measurable RF heating was found.These results suggest that the RF shield could be a valuable tool for clinical MRI practices.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiology, Mayo Clinic, Rochester, MN, USA.

ABSTRACT
Radiofrequency (RF) shields have been recently developed for the purpose of shielding portions of the patient's body during magnetic resonance imaging (MRI) examinations. We present an experimental evaluation of a commercially available RF shield in the MRI environment. All tests were performed on 1.5 T and 3.0 T clinical MRI scanners. The tests were repeated with and without the RF shield present in the bore, for comparison. Effects of the shield, placed within the scanner bore, on the RF fields generated by the scanner were measured directly using tuned pick-up coils. Attenuation, by as much as 35 dB, of RF field power was found inside the RF shield. These results were supported by temperature measurements of metallic leads placed inside the shield, in which no measurable RF heating was found. In addition, there was a small, simultaneous detectable increase (∼1 dB) of RF power just outside the edges of the shield. For these particular scanners, the autocalibrated RF power levels were reduced for scan locations prescribed just outside the edges of the shield, which corresponded with estimations based on the pick-up coil measurements. Additionally, no significant heating during MRI scanning was observed on the shield surface. The impact of the RF shield on the RF fields inside the magnet bore is likely to be dependent on the particular model of the RF shield or the MRI scanner. These results suggest that the RF shield could be a valuable tool for clinical MRI practices.

No MeSH data available.


Schematic of the experimental set-up used to measure heating of the surface of the RF shield.Notes: The dashed lines represent the temperature probes positioned on the interior surface of the shield. The solid lines represent the temperature probes positioned on the exterior surface of the shield.Abbreviation: RF, radiofrequency.
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f3-mder-7-363: Schematic of the experimental set-up used to measure heating of the surface of the RF shield.Notes: The dashed lines represent the temperature probes positioned on the interior surface of the shield. The solid lines represent the temperature probes positioned on the exterior surface of the shield.Abbreviation: RF, radiofrequency.

Mentions: To evaluate RF heating of the shield’s surface, the shield was tightly wrapped around the ASTM phantom, and four fluoroptic probes were attached to the shield at selected locations. Probe pairs were placed 2 cm from the superior edge and in the center of the shield, with one probe on each of the exterior and interior surfaces. The set-up was placed directly on the scanner bed and advanced into the bore with the superior edge of the shield positioned 15.5 cm from the isocenter. The probe positions and experimental set-up are shown in Figure 3. A 4-echo RF spin echo pulse sequence was performed. The relevant pulse sequence parameters were the same as listed in Table 1. TG was held constant at each field strength, 14.0 dB at 1.5 T and 13.1 dB at 3.0 T. Temperature history at each probe location was sampled at one-second intervals.


Use of a radio frequency shield during 1.5 and 3.0 Tesla magnetic resonance imaging: experimental evaluation.

Favazza CP, King DM, Edmonson HA, Felmlee JP, Rossman PJ, Hangiandreou NJ, Watson RE, Gorny KR - Med Devices (Auckl) (2014)

Schematic of the experimental set-up used to measure heating of the surface of the RF shield.Notes: The dashed lines represent the temperature probes positioned on the interior surface of the shield. The solid lines represent the temperature probes positioned on the exterior surface of the shield.Abbreviation: RF, radiofrequency.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4219642&req=5

f3-mder-7-363: Schematic of the experimental set-up used to measure heating of the surface of the RF shield.Notes: The dashed lines represent the temperature probes positioned on the interior surface of the shield. The solid lines represent the temperature probes positioned on the exterior surface of the shield.Abbreviation: RF, radiofrequency.
Mentions: To evaluate RF heating of the shield’s surface, the shield was tightly wrapped around the ASTM phantom, and four fluoroptic probes were attached to the shield at selected locations. Probe pairs were placed 2 cm from the superior edge and in the center of the shield, with one probe on each of the exterior and interior surfaces. The set-up was placed directly on the scanner bed and advanced into the bore with the superior edge of the shield positioned 15.5 cm from the isocenter. The probe positions and experimental set-up are shown in Figure 3. A 4-echo RF spin echo pulse sequence was performed. The relevant pulse sequence parameters were the same as listed in Table 1. TG was held constant at each field strength, 14.0 dB at 1.5 T and 13.1 dB at 3.0 T. Temperature history at each probe location was sampled at one-second intervals.

Bottom Line: Attenuation, by as much as 35 dB, of RF field power was found inside the RF shield.These results were supported by temperature measurements of metallic leads placed inside the shield, in which no measurable RF heating was found.These results suggest that the RF shield could be a valuable tool for clinical MRI practices.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiology, Mayo Clinic, Rochester, MN, USA.

ABSTRACT
Radiofrequency (RF) shields have been recently developed for the purpose of shielding portions of the patient's body during magnetic resonance imaging (MRI) examinations. We present an experimental evaluation of a commercially available RF shield in the MRI environment. All tests were performed on 1.5 T and 3.0 T clinical MRI scanners. The tests were repeated with and without the RF shield present in the bore, for comparison. Effects of the shield, placed within the scanner bore, on the RF fields generated by the scanner were measured directly using tuned pick-up coils. Attenuation, by as much as 35 dB, of RF field power was found inside the RF shield. These results were supported by temperature measurements of metallic leads placed inside the shield, in which no measurable RF heating was found. In addition, there was a small, simultaneous detectable increase (∼1 dB) of RF power just outside the edges of the shield. For these particular scanners, the autocalibrated RF power levels were reduced for scan locations prescribed just outside the edges of the shield, which corresponded with estimations based on the pick-up coil measurements. Additionally, no significant heating during MRI scanning was observed on the shield surface. The impact of the RF shield on the RF fields inside the magnet bore is likely to be dependent on the particular model of the RF shield or the MRI scanner. These results suggest that the RF shield could be a valuable tool for clinical MRI practices.

No MeSH data available.