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Temperature measurement on neurological pulse generators during MR scans.

Kainz W, Neubauer G, Uberbacher R, Alesch F, Chan DD - Biomed Eng Online (2002)

Bottom Line: Temperature increases in other locations were low compared to the one at the lead tip.The measured temperature increase of 2.1 degrees C can not be considered as harmful to the patient.Comparison with the results of other studies revealed the avoidance of loops as a practical method to reduce heating during MRI procedures.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Mobile Communications Safety, ARC Seibersdorf Research, Austria. kainz@gmx.com

ABSTRACT
According to manufacturers of both magnetic resonance imaging (MRI) machines, and implantable neurological pulse generators (IPGs), MRI is contraindicated for patients with IPGs. A major argument for this restriction is the risk to induce heat in the leads due to the electromagnetic field, which could be dangerous for the surrounding brain parenchyma. The temperature change on the surface of the case of an ITREL-III (Medtronic Inc., Minneapolis, MN) and the lead tip during MRI was determined. An anatomical realistic and a cubic phantom, filled with phantom material mimicking human tissue, and a typical lead configuration were used to imitate a patient who carries an IPG for deep brain stimulation. The measurements were performed in a 1.5 T and a 3.0 T MRI. 2.1 degrees C temperature increases at the lead tip uncovered the lead tip as the most critical part concerning heating problems in IPGs. Temperature increases in other locations were low compared to the one at the lead tip. The measured temperature increase of 2.1 degrees C can not be considered as harmful to the patient. Comparison with the results of other studies revealed the avoidance of loops as a practical method to reduce heating during MRI procedures.

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Related in: MedlinePlus

Phantom used in the 1.5 T MRI
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Figure 1: Phantom used in the 1.5 T MRI

Mentions: The temperature measurements were performed in vitro using a phantom especially developed for examinations with the ITREL-III (Medtronic Inc., Minneapolis, MN). The examinations were carried out on one implant, with standard electrodes (Medtronic Type # 3387) and leads with a length of 51 centimeter (cm). The neurostimulator was placed in the upper left quadrant of the thorax portion of the phantom. The placement was within 1 cm of the phantom surface. During the measurements the ITREL-III was set to the "off" mode (i.e. no stimulation output). The extensions were connected to the neurostimulator and the excess lengths were wrapped once around the implant case. The lead was positioned with a small single loop (3.5 cm in diameter) at the skull and 7 cm deep into the head perpendicular to the surface of the skull. This positioning corresponds to a typical placement of the ITREL-III in deep brain stimulation. The phantom consisted of three parts: the skull, the trunk and the skull-trunk connecting tube (see Fig. 1). The skull-trunk connection tube of the phantom established the electrical connection between the two liquid phantom materials (brain and muscle liquid) without mixing the liquids. The inside diameter of the connection tube measured 44 mm and was filled with a jelly phantom material imitating muscle tissue. The skull and trunk was filled with phantom materials mimicking brain and muscle tissue. The ingredients of the phantom materials are listed in Table 1. Temperature measurements in a radio frequency environment require materials that have the following characteristics: correct dielectric properties and correct specific thermal constant. New phantom materials [9] were developed for brain and muscle tissue. They were liquid and mixed according to the dielectric properties given for 63.6 MHz. This frequency corresponded to the frequency of the frequently used 1.5 T MRI. The parameters of the phantom liquids (the permittivity, the conductivity and the specific thermal constant) were all within an acceptable range. The dielectric properties of human tissue were taken from [7]. Properties of the phantom liquids were measured with the "Dielectric Probe Measurement System" HP 85070 from Hewlett Packard. The thermal constant was measured by a method described in [8]. Table 2. summarizes the dielectric properties of human tissue and phantom materials.


Temperature measurement on neurological pulse generators during MR scans.

Kainz W, Neubauer G, Uberbacher R, Alesch F, Chan DD - Biomed Eng Online (2002)

Phantom used in the 1.5 T MRI
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC130994&req=5

Figure 1: Phantom used in the 1.5 T MRI
Mentions: The temperature measurements were performed in vitro using a phantom especially developed for examinations with the ITREL-III (Medtronic Inc., Minneapolis, MN). The examinations were carried out on one implant, with standard electrodes (Medtronic Type # 3387) and leads with a length of 51 centimeter (cm). The neurostimulator was placed in the upper left quadrant of the thorax portion of the phantom. The placement was within 1 cm of the phantom surface. During the measurements the ITREL-III was set to the "off" mode (i.e. no stimulation output). The extensions were connected to the neurostimulator and the excess lengths were wrapped once around the implant case. The lead was positioned with a small single loop (3.5 cm in diameter) at the skull and 7 cm deep into the head perpendicular to the surface of the skull. This positioning corresponds to a typical placement of the ITREL-III in deep brain stimulation. The phantom consisted of three parts: the skull, the trunk and the skull-trunk connecting tube (see Fig. 1). The skull-trunk connection tube of the phantom established the electrical connection between the two liquid phantom materials (brain and muscle liquid) without mixing the liquids. The inside diameter of the connection tube measured 44 mm and was filled with a jelly phantom material imitating muscle tissue. The skull and trunk was filled with phantom materials mimicking brain and muscle tissue. The ingredients of the phantom materials are listed in Table 1. Temperature measurements in a radio frequency environment require materials that have the following characteristics: correct dielectric properties and correct specific thermal constant. New phantom materials [9] were developed for brain and muscle tissue. They were liquid and mixed according to the dielectric properties given for 63.6 MHz. This frequency corresponded to the frequency of the frequently used 1.5 T MRI. The parameters of the phantom liquids (the permittivity, the conductivity and the specific thermal constant) were all within an acceptable range. The dielectric properties of human tissue were taken from [7]. Properties of the phantom liquids were measured with the "Dielectric Probe Measurement System" HP 85070 from Hewlett Packard. The thermal constant was measured by a method described in [8]. Table 2. summarizes the dielectric properties of human tissue and phantom materials.

Bottom Line: Temperature increases in other locations were low compared to the one at the lead tip.The measured temperature increase of 2.1 degrees C can not be considered as harmful to the patient.Comparison with the results of other studies revealed the avoidance of loops as a practical method to reduce heating during MRI procedures.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Mobile Communications Safety, ARC Seibersdorf Research, Austria. kainz@gmx.com

ABSTRACT
According to manufacturers of both magnetic resonance imaging (MRI) machines, and implantable neurological pulse generators (IPGs), MRI is contraindicated for patients with IPGs. A major argument for this restriction is the risk to induce heat in the leads due to the electromagnetic field, which could be dangerous for the surrounding brain parenchyma. The temperature change on the surface of the case of an ITREL-III (Medtronic Inc., Minneapolis, MN) and the lead tip during MRI was determined. An anatomical realistic and a cubic phantom, filled with phantom material mimicking human tissue, and a typical lead configuration were used to imitate a patient who carries an IPG for deep brain stimulation. The measurements were performed in a 1.5 T and a 3.0 T MRI. 2.1 degrees C temperature increases at the lead tip uncovered the lead tip as the most critical part concerning heating problems in IPGs. Temperature increases in other locations were low compared to the one at the lead tip. The measured temperature increase of 2.1 degrees C can not be considered as harmful to the patient. Comparison with the results of other studies revealed the avoidance of loops as a practical method to reduce heating during MRI procedures.

Show MeSH
Related in: MedlinePlus