Calorimetric calibration of head coil SAR estimates displayed on a clinical MR scanner

Krzysztof R. Gorny, Matthew A Bernstein, Joel P. Felmlee, Heidi A. Ward, Kiaran Patrick McGee, Diana M. Lanners, Kendall H Lee

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

Calorimetric measurements were performed to determine the average specific absorption rates (SAR) resulting from MRI head examinations. The data were compared with average head coil SAR estimates displayed by the MR scanner in order to refine the imaging protocols used in imaging patients with implanted deep brain stimulators (DBS). The experiments were performed using transmit-receive (TR) head coil on clinical 1.5 T General Electric MR scanners running 11.0 M4 revision software. The average applied SAR was derived from temperature increases measured inside a head phantom, due to deposition of RF energy during MRI scanning with a spin echo imaging sequence. The measurements were repeated for varied levels of RF transmit gain (TG) and analyzed with a range of entered patient weights. The measurements demonstrate that the ratio of the actual average head SAR to the scanner-displayed value (coil correction factor) decreases for decreasing TG or for increasing patient weight and may vary between 0.3 and 2.1. An additional retrospective patient study, however, shows that not all combinations of TG and patient weight are encountered clinically and, instead, TG generally increases with the patient weight. As a result, a much narrower range of coil correction factors (e.g., typically 0.5-1.0) will be encountered in practice. The calorimetric method described in this work could aid the physicians and technologists in refinement of the model-dependent SAR estimates displayed by the MR scanner, and in selection of imaging parameters for MR head examinations within allowable SAR safety levels.

Original languageEnglish (US)
Pages (from-to)2565-2576
Number of pages12
JournalPhysics in Medicine and Biology
Volume53
Issue number10
DOIs
StatePublished - May 21 2008

Fingerprint

Calibration
scanners
coils
Head
Imaging techniques
estimates
Magnetic resonance imaging
Weights and Measures
examination
Brain
physicians
Scanning
Weight Gain
brain
safety
echoes
Software
Retrospective Studies
Magnetic Resonance Imaging
computer programs

ASJC Scopus subject areas

  • Biomedical Engineering
  • Radiology Nuclear Medicine and imaging
  • Physics and Astronomy (miscellaneous)
  • Radiological and Ultrasound Technology

Cite this

Calorimetric calibration of head coil SAR estimates displayed on a clinical MR scanner. / Gorny, Krzysztof R.; Bernstein, Matthew A; Felmlee, Joel P.; Ward, Heidi A.; McGee, Kiaran Patrick; Lanners, Diana M.; Lee, Kendall H.

In: Physics in Medicine and Biology, Vol. 53, No. 10, 21.05.2008, p. 2565-2576.

Research output: Contribution to journalArticle

Gorny, Krzysztof R. ; Bernstein, Matthew A ; Felmlee, Joel P. ; Ward, Heidi A. ; McGee, Kiaran Patrick ; Lanners, Diana M. ; Lee, Kendall H. / Calorimetric calibration of head coil SAR estimates displayed on a clinical MR scanner. In: Physics in Medicine and Biology. 2008 ; Vol. 53, No. 10. pp. 2565-2576.
@article{c96fe23a172345e98748ea617dc8d91f,
title = "Calorimetric calibration of head coil SAR estimates displayed on a clinical MR scanner",
abstract = "Calorimetric measurements were performed to determine the average specific absorption rates (SAR) resulting from MRI head examinations. The data were compared with average head coil SAR estimates displayed by the MR scanner in order to refine the imaging protocols used in imaging patients with implanted deep brain stimulators (DBS). The experiments were performed using transmit-receive (TR) head coil on clinical 1.5 T General Electric MR scanners running 11.0 M4 revision software. The average applied SAR was derived from temperature increases measured inside a head phantom, due to deposition of RF energy during MRI scanning with a spin echo imaging sequence. The measurements were repeated for varied levels of RF transmit gain (TG) and analyzed with a range of entered patient weights. The measurements demonstrate that the ratio of the actual average head SAR to the scanner-displayed value (coil correction factor) decreases for decreasing TG or for increasing patient weight and may vary between 0.3 and 2.1. An additional retrospective patient study, however, shows that not all combinations of TG and patient weight are encountered clinically and, instead, TG generally increases with the patient weight. As a result, a much narrower range of coil correction factors (e.g., typically 0.5-1.0) will be encountered in practice. The calorimetric method described in this work could aid the physicians and technologists in refinement of the model-dependent SAR estimates displayed by the MR scanner, and in selection of imaging parameters for MR head examinations within allowable SAR safety levels.",
author = "Gorny, {Krzysztof R.} and Bernstein, {Matthew A} and Felmlee, {Joel P.} and Ward, {Heidi A.} and McGee, {Kiaran Patrick} and Lanners, {Diana M.} and Lee, {Kendall H}",
year = "2008",
month = "5",
day = "21",
doi = "10.1088/0031-9155/53/10/008",
language = "English (US)",
volume = "53",
pages = "2565--2576",
journal = "Physics in Medicine and Biology",
issn = "0031-9155",
publisher = "IOP Publishing Ltd.",
number = "10",

}

TY - JOUR

T1 - Calorimetric calibration of head coil SAR estimates displayed on a clinical MR scanner

AU - Gorny, Krzysztof R.

AU - Bernstein, Matthew A

AU - Felmlee, Joel P.

AU - Ward, Heidi A.

AU - McGee, Kiaran Patrick

AU - Lanners, Diana M.

AU - Lee, Kendall H

PY - 2008/5/21

Y1 - 2008/5/21

N2 - Calorimetric measurements were performed to determine the average specific absorption rates (SAR) resulting from MRI head examinations. The data were compared with average head coil SAR estimates displayed by the MR scanner in order to refine the imaging protocols used in imaging patients with implanted deep brain stimulators (DBS). The experiments were performed using transmit-receive (TR) head coil on clinical 1.5 T General Electric MR scanners running 11.0 M4 revision software. The average applied SAR was derived from temperature increases measured inside a head phantom, due to deposition of RF energy during MRI scanning with a spin echo imaging sequence. The measurements were repeated for varied levels of RF transmit gain (TG) and analyzed with a range of entered patient weights. The measurements demonstrate that the ratio of the actual average head SAR to the scanner-displayed value (coil correction factor) decreases for decreasing TG or for increasing patient weight and may vary between 0.3 and 2.1. An additional retrospective patient study, however, shows that not all combinations of TG and patient weight are encountered clinically and, instead, TG generally increases with the patient weight. As a result, a much narrower range of coil correction factors (e.g., typically 0.5-1.0) will be encountered in practice. The calorimetric method described in this work could aid the physicians and technologists in refinement of the model-dependent SAR estimates displayed by the MR scanner, and in selection of imaging parameters for MR head examinations within allowable SAR safety levels.

AB - Calorimetric measurements were performed to determine the average specific absorption rates (SAR) resulting from MRI head examinations. The data were compared with average head coil SAR estimates displayed by the MR scanner in order to refine the imaging protocols used in imaging patients with implanted deep brain stimulators (DBS). The experiments were performed using transmit-receive (TR) head coil on clinical 1.5 T General Electric MR scanners running 11.0 M4 revision software. The average applied SAR was derived from temperature increases measured inside a head phantom, due to deposition of RF energy during MRI scanning with a spin echo imaging sequence. The measurements were repeated for varied levels of RF transmit gain (TG) and analyzed with a range of entered patient weights. The measurements demonstrate that the ratio of the actual average head SAR to the scanner-displayed value (coil correction factor) decreases for decreasing TG or for increasing patient weight and may vary between 0.3 and 2.1. An additional retrospective patient study, however, shows that not all combinations of TG and patient weight are encountered clinically and, instead, TG generally increases with the patient weight. As a result, a much narrower range of coil correction factors (e.g., typically 0.5-1.0) will be encountered in practice. The calorimetric method described in this work could aid the physicians and technologists in refinement of the model-dependent SAR estimates displayed by the MR scanner, and in selection of imaging parameters for MR head examinations within allowable SAR safety levels.

UR - http://www.scopus.com/inward/record.url?scp=42649121625&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=42649121625&partnerID=8YFLogxK

U2 - 10.1088/0031-9155/53/10/008

DO - 10.1088/0031-9155/53/10/008

M3 - Article

C2 - 18441413

AN - SCOPUS:42649121625

VL - 53

SP - 2565

EP - 2576

JO - Physics in Medicine and Biology

JF - Physics in Medicine and Biology

SN - 0031-9155

IS - 10

ER -