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REVIEW 3 major objections 5 minor 19 references

Comparison of Magnetic Field Characteristics among 3 Tesla MRI Scanners: An Experimental Measurement Study

T0 review · 3 major / 5 minor · reviewed 2026-08-06 · deepseek-v4-flash

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Pith's one-line read Measured fringe fields around three 3 T MRI scanners differ by up to 0.5 T between manufacturers and 0.17 T between same-brand units, so site-specific mapping, not vendor diagrams, is needed for safety assessment.

desk verdict Useful dataset showing fringe-field variability across 3T sites, but the headline same-manufacturer differences rest on mirrored and interpolated data and need a clear caveat. read the letter →

arxiv 2507.20818 v1 pith:NCR4EGUW submitted 2025-07-28 physics.med-ph

Francesco Girardello , Maria Antonietta D'Avanzo , Massimo Mattozzi , Victorian Michele Ferro , Giuseppe Acri , Valentina Hartwig This is my paper
classification physics.med-ph
keywords MRIfringefield3Teslascannercomparisonexperimentalmagneticmappingsite-specificdistributionsafetyoccupationalexposurestaticspatialgradient
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

The paper tries to establish that the magnetic fringe field around a 3 Tesla MRI scanner is an installation-specific quantity, not a fixed property of the magnet or its nominal field strength. The authors measured the field on a 10 cm grid beside three clinical scanners, fitted and interpolated the data into three-dimensional maps, and computed spatial gradients from those maps. They found maximum differences of 0.5 T in field strength and 1.64 T/m in spatial gradient between scanners of different manufacturers, and still 0.17 T and 0.5 T/m between two scanners of the same manufacturer. If the result is correct, manufacturer-supplied isogauss line plans cannot define the zones where staff are exposed to high fields or steep gradients; each installation would need its own post-installation measurement.

What carries the argument

The argument is carried by a measurement-plus-interpolation pipeline rather than by a single equation. A commercial magnetometer records the field magnitude on a $10 \times 10\,\mathrm{cm}$ grid on the right side of each scanner at three heights (waist, chest, and head/eyes); a nonlinear least-squares fitter selects among roughly ten parametric functions, including $f_{\mathrm{exp}}(\boldsymbol{b},x) = b_1 e^{-b_2 x} + b_3 e^{-b_4 x} + b_5 e^{-b_6 x}$ and variants with polynomial prefactors, using the reduced chi-squared $\chi^2_{\mathrm{red}}$ closest to unity. The fitted rows and columns are interpolated to volumetric maps, and the field is mirrored across the plane through the isocenter perpendicular to the patient table to double the number of available planes. The spatial gradient magnitude is then computed from partial derivatives of the interpolated field with a 1 cm step, and uncertainties are combined quadratically from instrumental, fitting, and interpolation errors. This pipeline is what turns sparse point samples into the comparative maps and into the reported maximum differences.

What would settle it

Measure the fringe field on both the left and right sides of one of the three scanners on the same $10 \times 10\,\mathrm{cm}$ grid at the same three heights; if field magnitudes at mirrored points differ by more than the combined uncertainty, the unmeasured half of the reported maps — and any maximum difference located there — is a model artifact rather than a measurement.

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Extended reading notes

Core claim

On the paper's own terms, the discovery is that two 3 T scanners from the same manufacturer, installed in different hospitals, produce measurably different fringe fields and spatial gradients, and that the differences are larger still between manufacturers. The largest measured field difference was 0.5 T and the largest gradient difference was 1.64 T/m between different manufacturers; for the same-manufacturer pair the maxima were 0.17 T and 0.5 T/m. These maxima sit close to the gantry, in the zones where radiographers work during patient positioning. The authors conclude that the fringe field and spatial gradient differed across all sites despite the same nominal $B_0 = 3\,\mathrm{T}$, and that the generic information provided by manufacturers is insufficient for assessing worker exposure.

Load-bearing premise

The load-bearing premise is that the magnetic field is mirror-symmetric across the plane through the isocenter perpendicular to the patient table, so the left half of every map is not measured but copied from the right; the authors acknowledge that room layout and structural features may break this symmetry, and if it breaks, every field and gradient value on the unmeasured side is a model artifact.

Editorial extensions

If this is right

  • Safety zones drawn from manufacturer isogauss projections can be wrongly sized or placed, so commissioning of a 3 T scanner should include post-installation field mapping.
  • Two scanners of the same model and manufacturer can expose staff to measurably different fields, meaning room design and shielding, not nominal field strength, set the real fringe field.
  • The largest observed discrepancies sit at the gantry edge, exactly where technologists position patients, so the worst-case exposure point is where generic diagrams are least informative.
  • The measurement and interpolation protocol generalizes to other MRI suites once a minimum $70 \times 70\,\mathrm{cm}$ measurement area is covered, allowing comparable maps and gradients to be produced elsewhere.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • If the reflection symmetry across the plane perpendicular to the patient table is broken by room structure, the mirrored half of every map is a model artifact; a two-sided measurement would show whether the reported maxima are real, overestimated, or underestimated.
  • A practical extension the authors do not pursue is to couple these static gradient maps with recorded staff movement paths, because the biological exposure is set by the time-varying field along the worker's trajectory, not by the static map alone.
  • The three-site sample cannot separate shielding type from room geometry; repeating the protocol at sites with active versus passive shielding, and with documented structural layouts, would be needed to isolate the cause of the inter-manufacturer differences.
  • Because the maps were built from only three heights on one side, vertical gradients between planes are less constrained than horizontal ones; denser height sampling would tighten the volumetric reconstruction and test the symmetry assumption directly.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

3 major / 5 minor

Summary. The paper reports an experimental mapping of the static magnetic fringe field and its spatial gradient around three 3 T MRI scanners installed at three Italian hospitals, two of which are from the same manufacturer. Measurements were taken on a 10×10 cm grid on the right side of the patient table at three heights, then extended to full-room volumetric maps using parametric fitting, interpolation, and mirroring about the y-axis. The authors compare pairwise field and gradient differences and report maximum differences of up to 0.5 T and 1.64 T/m between scanners of different manufacturers, and up to 0.17 T and 0.5 T/m between scanners of the same manufacturer (Tables 3 and 4). They conclude that manufacturer-provided isogauss lines are insufficient for site-specific safety assessments.

Significance. If the quantitative claims were fully supported, the paper would be a valuable addition to MRI safety literature, providing concrete evidence that fringe fields vary across installations even for identical nominal field strength. The study's qualitative conclusion that scanners differ in their fringe fields is credible and consistent with prior work, and the direct measurement protocol near the gantry is a useful contribution. The principal limitation is that the headline quantitative maxima—especially the same-manufacturer differences—are not direct measurements but are generated by parametric fitting and by mirroring measured data across a symmetry plane that the authors themselves concede may not hold. The manuscript also introduces interpolation-uncertainty constants without calibration. These issues undercut the quantitative strength of the central claim, though they can be addressed in revision by restricting claims to measured regions, providing left-side measurements, or presenting the maxima as model-dependent estimates.

major comments (3)
  1. [Section 3 (Data Processing) and Tables 3–4] The maximum same-manufacturer differences in Tables 3 and 4 occur at negative x coordinates (e.g., Table 3, MRI-2 vs MRI-3, XZ: x=-70, y=0, z=85; Table 4, MRI-2 vs MRI-3, XZ: x=-50, y=0, z=-74). These positions lie on the left side of the scanner, which per Section 3 was not measured but generated by mirroring the right-side measurements under the assumption of symmetry about the y-axis. Section 5 concedes that this assumption 'may not hold true due to the distinct configuration of the room and its structural characteristics.' Consequently, the quantitative support for the claim that same-manufacturer scanners differ is not based on direct measurements at the reported maxima. Additionally, the y=0 plane used in the XZ rows of Tables 3 and 4 is interpolated between the measured y=-5 and y=25 cm planes. The authors should either measure the left side at the reported maxima, or restrict the quantitative comparisons to the directly measured side and clearly label mirrored regions as model-dependent.
  2. [Section 3, Eqs. (5)–(6)] Equation (5) defines the interpolation uncertainty as σ_interp = σ_i + α × d_min with σ_i = 3% and α = 0.05%/cm, but these constants are asserted rather than derived or calibrated. They propagate into the total uncertainty in Eq. (6) and therefore into all error bars in Tables 3–6. Several reported maximum differences are comparable to or smaller than these uncertainties (e.g., Table 3, MRI-2 vs MRI-3, XZ: -0.17 ± 0.15 T; Table 4, MRI-2 vs MRI-3, YZ: 0.30 ± 0.17 T/m), so a different but equally plausible choice of σ_i or α could change which differences are statistically significant. The authors should justify the constants from data, for example through repeated measurements at varying distances, or provide a sensitivity analysis.
  3. [Section 3 (Model selection) and Section 4 (Tables 3–4)] The field and gradient maps used to compute the maximum differences are not raw measurements but outputs of a two-stage procedure: each row and column is fitted with one of about ten parametric functions with five or six free parameters, with the model chosen by reduced χ² closest to unity, and then the outermost regions are filled by interpolation and mirroring. The manuscript does not report the spatial distribution of fit residuals, nor does it validate the fitted maps against held-out measurements. The largest same-manufacturer difference in Table 3 occurs at x=-70, z=85, which is in the extrapolated/mirrored region. The qualitative result that scanners differ is supported by direct measurements near the gantry, but the quantitative maxima should be presented with explicit caveats about model dependence, or supported by independent validation measurements.
minor comments (5)
  1. [Section 4, Tables 3 and 4] Tables 3 and 4 appear to be mislabeled or displayed in reverse order: the data block with gradient values (labeled 'Table 4') appears before the data block with field values (labeled 'Table 3'), and both captions are printed consecutively before either table's data. Please reorder so that each table immediately follows its caption.
  2. [Section 5, Discussion item 3] Discussion item 3 refers to 'Tables 4 and 5' when the magnetic field and gradient differences are presented in Tables 3 and 4; please correct the cross-references.
  3. [Section 2, Methodology] The text states that a minimum of 120 data points were collected per plane on a 10×10 cm grid, but a 10×10 grid over the red box in Figure 1 would contain far more than 120 points unless the grid covers only a partial region; please clarify the actual grid extent and point count.
  4. [References] Reference 3 shares the same DOI as Reference 2 (10.1007/s11517-021-02435-6); please verify and correct the DOI for the 2022 paper by Hartwig et al.
  5. [Section 3, Eq. (4)] In Eq. (4), the symbol B_i is used without an explicit definition in the equation itself (it is defined only in the surrounding text); consider adding a notation explanation for clarity.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the study is an empirical measurement and interpolation comparison, with the symmetry assumption acknowledged as a limitation rather than a circular derivation.

full rationale

The paper reports an experimental mapping study: magnetic field values are measured with a gaussmeter on a grid, fitted to parametric functions, interpolated into volumetric maps, and then compared across three scanners. No claim is derived from a first-principles model whose output is equivalent to its input. The fitting functions (Eqs. 1–3) are chosen to represent the measured decay profiles, and the reduced chi-squared selection (Eq. 4) is a standard model-selection criterion; the fitted parameters are not later relabeled as a 'prediction' of an independent quantity. The maximum-difference values in Tables 3–6 are read off the constructed maps, so they are contingent on the fitting and interpolation procedure, but that is a normal property of any measurement-plus-interpolation study, not a circular reduction. The symmetry assumption used to mirror right-side measurements to the left side is explicitly stated and its failure is acknowledged in Section 5 ('this assumption may not hold true due to the distinct configuration of the room and its structural characteristics'). This is a correctness or robustness limitation concerning unmeasured regions, not a circular argument: the mirrored values are not used to justify the assumption itself. The uncertainty model in Eq. (5) contains free constants (3% intrinsic uncertainty, 0.05% per cm), but these are arbitrary parameter choices rather than circular inputs. Self-citations (e.g., Hartwig et al. for the measurement protocol) are used as methodological support, but the central comparison does not reduce to those references; the measurements were performed independently at three sites. No uniqueness theorem or ansatz is imported from the authors' prior work to force the conclusions. Overall, the derivation chain is empirical and self-contained; the main risks are assumption-validity and generalizability, not circularity.

Assumptions & free parameters 3 free parameters · 4 assumptions · 0 invented entities

The analysis introduces no new physical entities. It relies on modeling assumptions about field structure and symmetry, plus fitted coefficients and chosen uncertainty constants. The headline comparison numbers are products of these modeling choices rather than direct measurements.

free parameters (3)
  • Coefficients of parametric fitting functions (b1-b6, a1-a5) for Eqs. (1)-(3) and related functions = Not reported (fit per region and plane)
    Approximately 20 fits per measurement plane per scanner, each with 5-6 free parameters, are used to extrapolate the measured grid values to the entire room. These coefficients are fitted to the data, not derived.
  • Interpolation error constants sigma_i and alpha in Eq. (5) = 3 percent and 0.05 percent per cm
    These quantify how interpolation uncertainty grows with distance from measurement points. They are asserted without a calibration or formal derivation, so they are free parameters of the uncertainty model.
  • Model selection rule: reduced chi-squared closest to unity = n/a
    The choice among about ten candidate functions per spatial region is a modeling decision that affects the extrapolated field values and therefore the computed differences.
assumptions (4)
  • domain assumption The static magnetic fringe field in air can be represented as a scalar magnitude map and modeled by combinations of exponential and polynomial functions (Eqs. 1-3) over the whole room.
    Section 3 uses this to extend measurements beyond the measured grid. The candidate functions are not derived from magnetostatic theory and no independent validation is provided.
  • domain assumption The fringe field is symmetric about the y-axis (the plane through the isocenter perpendicular to the patient table).
    Section 3 leverages this to double the number of planes and fill the unmeasured side. Section 5 acknowledges the symmetry may be broken by room configuration.
  • domain assumption Three horizontal measurement planes (at approximately waist, chest, and head height) are sufficient to reconstruct the three-dimensional field by interpolation.
    Section 3 states a minimum of three complete planes is needed, but the accuracy of vertical interpolation between them is not assessed.
  • domain assumption The measurement protocol of Hartwig et al. (ref 9) is valid and applicable to these three sites.
    Section 2 says the acquisition followed that validated protocol, but no validation data or independent check is presented in this paper.

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Cite this review

Pith. "Pith review of Comparison of Magnetic Field Characteristics among 3 Tesla MRI Scanners: An Experimental Measurement Study." pith.science (2026). https://pith.science/paper/NCR4EGUW

@misc{pith2026250720818,
  author       = {Pith},
  title        = {Pith review of: Comparison of Magnetic Field Characteristics among 3 Tesla MRI Scanners: An Experimental Measurement Study},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/NCR4EGUW}},
  note         = {Machine review of arXiv:2507.20818}
}
read the original abstract

Magnetic resonance imaging (MRI) scanners have advanced significantly, with a growing use of highfield 3 T systems. This evolution gives rise to safety concerns for healthcare personnel working in proximity to MRI equipment. While manufacturers provide theoretical Gauss line projections, these are typically derived under ideal open-environment conditions and may not reflect real-world installations. For this reason, identical MRI models can produce markedly different fringe field distributions depending on shielding and room configurations. The present study proposes an experimental methodology for the mapping of the fringe magnetic field in the vicinity of three 3 T MRI scanners. Field measurements were interpolated to generate threedimensional magnetic field maps. A comparative analysis was conducted, which revealed notable differences among the scanners. These differences serve to highlight the influence of site-specific factors on magnetic field propagation.

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Reference graph

Works this paper leans on

19 extracted references · 17 canonical work pages

  1. [1]

    With regard to the magnetic field, it can be observed that there is a maximum difference of 0.5 T between scanners from different manufacturers, while the maximum difference is reduced to 0.17 T when comparing the two scanners from the same manufacturer. In both cases, the maximum observed difference was located at the edge of the gantry: in the first cas...

    work page

  2. [2]

    With regard to the spatial gradient, it can be observed that there is a maximum difference of 1.64 T/m between scanners from different manufacturers, while the maximum difference is reduced to 0.5 T/m when comparing the two scanners from the same manufacturer. As demonstrated in Figures 11 and 12, there is a significant disparity in the spatial gradient v...

    work page

  3. [3]

    In an effort to generalise, it can be stated that the most significant discrepancies in absolute terms are located in close proximity to the gantry

    As shown by Tables 4 and 5, the differences for the magnetic field and its spatial gradient are highly dependent on the location in the space around the MRI scanner. In an effort to generalise, it can be stated that the most significant discrepancies in absolute terms are located in close proximity to the gantry. By fixing the position of a specific point...

    work page

  4. [4]

    A comprehensive review on magnetic imaging techniques for biomedical applications

    Mukhatov A, Le T, Pham TT, Do TD. A comprehensive review on magnetic imaging techniques for biomedical applications. Nano Sel. 2023;4(3):213–30 https://doi.org/10.1002/nano.202200219

    doi:10.1002/nano.202200219 2023

  5. [5]

    Occupational exposure to electromagnetic fields in magnetic resonance environment: basic aspects and review of exposure assessment approaches

    Hartwig V, Romeo S, Zeni O. Occupational exposure to electromagnetic fields in magnetic resonance environment: basic aspects and review of exposure assessment approaches. Med Biol Eng Comput. 2018;56(4):531–45 https://doi.org/10.1007/s11517-021- 02435-6

    work page doi:10.1007/s11517-021- 2018

  6. [6]

    Occupational exposure to electromagnetic fields in magnetic resonance environment: an update on regulation, exposure assessment techniques, health risk evaluation, and surveillance

    Hartwig V, Virgili G, Mattei F, Biagini C, Romeo S, Zeni O, et al. Occupational exposure to electromagnetic fields in magnetic resonance environment: an update on regulation, exposure assessment techniques, health risk evaluation, and surveillance. Med Biol Eng Comput. 2022;60(2):297–320 https://doi.org/10.1007/s11517-021-02435-6

    work page doi:10.1007/s11517-021-02435-6 2022

  7. [7]

    dB/dt evaluation in MRI sites: Is ICNIRP threshold limit (for workers) exceeded? Int J Environ Res Public Health

    Acri G, Inferrera P, Denaro L, Sansotta C, Ruello E, Anfuso C, et al. dB/dt evaluation in MRI sites: Is ICNIRP threshold limit (for workers) exceeded? Int J Environ Res Public Health. 2018;15(7):1–13 https://doi.org/10.3390/ijerph15071298

    work page doi:10.3390/ijerph15071298 2018

  8. [8]

    Essentials of MRI safety

    McRobbie DW. Essentials of MRI safety. Hoboken, New Jersey, US: Wiley-Blackwell; 2020. 392 p

    work page 2020

Show all 19 references
  1. [9]

    Subjective symptoms in Magnetic Resonance Imaging operators: prevalence, short-term evolution and possible related factors

    Zanotti G, Ligabue G, Korpinen L, Gobba F. Subjective symptoms in Magnetic Resonance Imaging operators: prevalence, short-term evolution and possible related factors. Med del Lav. 2016;107(4):263–70 https://doi.org/10.23749/mdl.v107i4.5240

    2016 doi

  2. [10]

    Health complaints among nurses working near MRI scanners — A descriptive pilot study

    Wilén J, Vocht F De. Health complaints among nurses working near MRI scanners — A descriptive pilot study. Eur J Radiol. 2011;80(2):510–3 https://doi.org/10.1016/j.ejrad.2010.09.021

    2011 doi

  3. [11]

    The Procedure for Quantitative Characterization and Analysis of Magnetic Fields in Magnetic Resonance Sites for Protection of Workers: A Pilot Study

    Hartwig V, Biagini C, De Marchi D, Flori A, Gabellieri C, Virgili G, et al. The Procedure for Quantitative Characterization and Analysis of Magnetic Fields in Magnetic Resonance Sites for Protection of Workers: A Pilot Study. Ann Work Expo Heal. 2019;63(3):1–9 https://doi.org/...

    2019 doi

  4. [12]

    Assessment of Exposure to Spatially Varying Magnetic Fields in MRI Environments: Modeling Analysis for Simulation Tools

    Hartwig V, Cianfaglione M, Campanella F, D’Avanzo MA, Sansotta C, Acri G. Assessment of Exposure to Spatially Varying Magnetic Fields in MRI Environments: Modeling Analysis for Simulation Tools. IEEE Access. 2024;12(January):11492–9 https://doi.org/ 10.1109/ACCESS.2024.3355191

    2024

  5. [13]

    An Investigation into Occupational Exposure to Electromagnetic Fields for Personnel Working With and Around Medical Magnetic Resonance Imaging Equipment

    Capstick M, McRobbie D, Hand JW, Christ A, Kuhn S, Hansson K, et al. An Investigation into Occupational Exposure to Electromagnetic Fields for Personnel Working With and Around Medical Magnetic Resonance Imaging Equipment. 2008

    2008

  6. [14]

    The Concise Encyclopedia of Statistics

    Dodge Y. The Concise Encyclopedia of Statistics. The Concise Encyclopedia of Statistics. Springer New York; 2008

    2008

  7. [15]

    The propagation of uncertainty with calibration equations

    White DR, Saunders P. The propagation of uncertainty with calibration equations. Meas Sci Technol. 2007;18(7):2157–69 https://doi.org/10.1088/0957- 0233/18/7/047

    2007 doi

  8. [16]

    Anthropometric Calculator (Male) [Internet]

    OHCOW. Anthropometric Calculator (Male) [Internet]. [cited 2025 May 27]. Available from: https://www.ohcow.on.ca/resources/apps-tools- calculators/anthropometric-calculator-2024/en/male/

    2025

  9. [17]

    ACR guidance document on MR safe practices: Updates and critical information

    Greenberg TD, Hoff MN, Gilk TB, Jackson EF, Kanal E, McKinney AM, et al. ACR guidance document on MR safe practices: Updates and critical information

  10. [19]

    Safety Evaluation of MRI Magnetic Field Leakage from Different Configurations

    Hong YS, Aisyah S, Nordin M, Mustajfa M, Kechik A, Khalis M, et al. Safety Evaluation of MRI Magnetic Field Leakage from Different Configurations. J Mater Sci Radiat. 2025;1(1):7–14. Contribution of Individual Authors to the Creation of a Scientific Article (Ghostwriting Pol i...

    2025

  11. [2019]

    2020;51(2):331–8 https://doi.org/10.1002/jmri.26880

    J Magn Reson Imaging. 2020;51(2):331–8 https://doi.org/10.1002/jmri.26880

    2020 doi

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