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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 for RF heating of metallic lead measurements, which shows the positions of the copper wires relative to the phantom, RF shield, and fluoroptic temperature probes.Abbreviation: RF, radiofrequency.
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f2-mder-7-363: Schematic of the experimental set-up for RF heating of metallic lead measurements, which shows the positions of the copper wires relative to the phantom, RF shield, and fluoroptic temperature probes.Abbreviation: RF, radiofrequency.

Mentions: Suppression of the RF field inside the shield should translate into a reduction of RF-induced heating of metallic leads. To investigate this, we measured temperature increases at the tips of metallic leads placed in a head-and-torso ASTM phantom (ASTM F2182-11) filled with gelled saline.14 Three 18-gauge, 40 cm long, straight copper wires were placed parallel to the scanner z-axis, positioned 20 cm apart, and completely submerged in the ASTM phantom, as depicted in Figure 2. The wires were fully insulated except for the 5 mm long bare tips. Fluoroptic temperature probes (STF-2, model 750; LumaSense Inc., Santa Clara, CA, USA) were positioned at the tip of each of the wires and a fourth probe was used to monitor the ambient temperature of the phantom. A 4-echo spin echo pulse sequence was subsequently executed for 6 minutes and 25 seconds to generate RF heating. The relevant pulse sequence parameters are listed in Table 1. TG was held constant at each field strength, 15.8 dB at 1.5 T and 13.3 dB at 3.0 T.


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 for RF heating of metallic lead measurements, which shows the positions of the copper wires relative to the phantom, RF shield, and fluoroptic temperature probes.Abbreviation: RF, radiofrequency.
© Copyright Policy
Related In: Results  -  Collection

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

f2-mder-7-363: Schematic of the experimental set-up for RF heating of metallic lead measurements, which shows the positions of the copper wires relative to the phantom, RF shield, and fluoroptic temperature probes.Abbreviation: RF, radiofrequency.
Mentions: Suppression of the RF field inside the shield should translate into a reduction of RF-induced heating of metallic leads. To investigate this, we measured temperature increases at the tips of metallic leads placed in a head-and-torso ASTM phantom (ASTM F2182-11) filled with gelled saline.14 Three 18-gauge, 40 cm long, straight copper wires were placed parallel to the scanner z-axis, positioned 20 cm apart, and completely submerged in the ASTM phantom, as depicted in Figure 2. The wires were fully insulated except for the 5 mm long bare tips. Fluoroptic temperature probes (STF-2, model 750; LumaSense Inc., Santa Clara, CA, USA) were positioned at the tip of each of the wires and a fourth probe was used to monitor the ambient temperature of the phantom. A 4-echo spin echo pulse sequence was subsequently executed for 6 minutes and 25 seconds to generate RF heating. The relevant pulse sequence parameters are listed in Table 1. TG was held constant at each field strength, 15.8 dB at 1.5 T and 13.3 dB at 3.0 T.

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.