MR Phantoms
What does an MR phantom look like?
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ACR large phantom |
The American College of Radiology (ACR) large MR phantom is an 8" diameter acrylic cylinder filled with a solution of 45 mM NaCl and 10 mM NiCl2 to simulate biological conductivity. Various internal structures are present made of glass or plastic. These include: 1) a central grid to assess geometric accuracy and linearity/distortion; 2) a uniform region to assess signal intensity; 3) wedges for slice position measurement; 4) ramps for slice thickness measurement; 5) shallow holes for low contrast detectability/measurement; 6) small holes for spatial resolution; 7) a vial of concentrated NiCl2 solution with different T1 and T2 values; and 8) a vial of vegetable fat. Typical images obtained through various parts of the phantom are shown below:
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Image through grid
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T1 sagittal
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T1 axial
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T2 axial
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Resolution image
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The ACR also offers a small (4.5-inch diameter) MRI phantom designed to fit within the scanner's standard knee coil and having similar construction to the larger phantom.
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Especially popular in Europe is the Eurospin II Test System, a set of 5 short cylindrical phantoms each designed to measure specific quality parameters: TO1 (uniformity, SNR, ghosting), TO2 (slice profile, width, geometric distortion), TO3 (slice position and warp), TO4 (resolution via bar pattern and modulation transfer function), and TO5 (a chamber with 12 cavities into which vials of tissue-mimicking gels can be inserted to measure T1/T2 precision, accuracy, and contrast).
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Eurospin II Test System Phantoms
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A variety of other specialized MR phantoms can be found. A few are pictured below.
Surface coil phantom
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Breast phantom
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Phantom from National Institute of Standards and Technology (NIST)
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In the future we may expect to see many more generalized and special purpose phantoms including structural brain phantoms, dynamic contrast enhanced perfusion phantoms, diffusion and diffusion tensor phantoms, flow phantoms, spectroscopy phantoms, and fat fraction phantoms.
References
American College of Radiology. Phantom test guidance for use of the large MRI phantom for the ACR accreditation program, 2018.
American College of Radiology. Phantom test guidance for use of the small MRI phantom for the ACR accreditation program, 2018.
Keenan KE, Ainslie M, Barker AJ, et al. Quantitative magnetic resonance imaging phantoms: a review and the need for a system phantom. Magn Reson Med 2018; 79:48-61. [DOI Link]
Lerski RA. Trial of modifications to Eurospin MRI test objects. Magn Reson Imaging 1993; 11:835-839. [DOI Link]
Ultrasound Enterprises Ltd. Product specifications for Eurospin II Test System. (downloaded July 2020)
American College of Radiology. Phantom test guidance for use of the large MRI phantom for the ACR accreditation program, 2018.
American College of Radiology. Phantom test guidance for use of the small MRI phantom for the ACR accreditation program, 2018.
Keenan KE, Ainslie M, Barker AJ, et al. Quantitative magnetic resonance imaging phantoms: a review and the need for a system phantom. Magn Reson Med 2018; 79:48-61. [DOI Link]
Lerski RA. Trial of modifications to Eurospin MRI test objects. Magn Reson Imaging 1993; 11:835-839. [DOI Link]
Ultrasound Enterprises Ltd. Product specifications for Eurospin II Test System. (downloaded July 2020)