arxiv: 2604.23075 · v1 · submitted 2026-04-25 · ⚛️ physics.med-ph · physics.ins-det

Recognition: unknown

Design and Optimization of a Pole-less 0.2 T C-Type MRI Magnet

Ivan Etoku Oiye , Ajay Sharma , Sairam Geethanath

Authors on Pith no claims yet

Pith reviewed 2026-05-08 07:03 UTC · model grok-4.3

classification ⚛️ physics.med-ph physics.ins-det

keywords low-field MRIpermanent magnet designC-type magnetpole-less MRImagnetic field homogeneityMRI magnet optimization0.2 T MRI

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The pith

A pole-less C-type permanent magnet reaches 0.2 T field strength with 590 kg weight by using concentric rings instead of pole pieces.

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

The paper shows that a C-shaped yoked magnet for low-field MRI can be built without traditional pole pieces by using two cylindrical permanent magnets surrounded by four concentric rings. Geometric parameters such as ring thickness, height, spacing, and vertical offset were adjusted in simulation to reach 0.2 T peak field with 1.43 mT inhomogeneity over a 20 cm diameter spherical volume. The resulting assembly weighs 590 kg, which is lighter than a comparable pole-piece design that only reached 0.15 T at 890 kg. This approach keeps the open C-structure for better patient access while meeting basic homogeneity needs for imaging.

Core claim

Replacing conventional pole pieces with four concentric magnet rings around two N52 cylindrical magnets in a bipolar C-type yoked structure produces a 0.2 T central field with 1.43 mT peak-to-peak inhomogeneity inside a 20 cm DSV at a total magnet weight of 590 kg, outperforming a benchmark pole-piece design of similar size that achieved only 0.15 T and 890 kg.

What carries the argument

The pole-less ring configuration, consisting of two cylindrical N52 permanent magnets and four concentric rings whose thicknesses, heights, angular positions, inter-magnet spacing, and vertical offsets relative to the yokes are manually tuned to shape the field inside the DSV.

If this is right

Reduces overall system weight enough to support mobile or point-of-care low-field scanners.
Preserves the open C-geometry that improves patient comfort and access compared with closed-bore designs.
Provides a direct weight and field-strength comparison showing rings can replace poles while raising central field from 0.15 T to 0.2 T.
Allows further parameter exploration in simulation to target tighter homogeneity or different DSV sizes without adding iron poles.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

The same ring-shaping method could be tested at 0.3 T or higher to see if the weight advantage scales before iron saturation becomes limiting.
A prototype measurement campaign would immediately reveal whether CST magnetostatic predictions overestimate or underestimate real-world inhomogeneity due to material tolerances or assembly errors.
If the ring approach generalizes, it may reduce the amount of rare-earth material needed per unit field strength in other yoked permanent-magnet geometries.

Load-bearing premise

Manual tuning of a small set of geometric parameters inside magnetostatic simulation produces a near-optimal design whose performance will match physical reality.

What would settle it

Fabricate the simulated 590 kg magnet and measure its actual field map inside a 20 cm DSV to check whether inhomogeneity stays below 1.43 mT and peak field reaches 0.2 T.

Figures

Figures reproduced from arXiv: 2604.23075 by Ajay Sharma, Ivan Etoku Oiye, Sairam Geethanath.

**Figure 1.** Figure 1: Geometric design variables, including the thickness and height of each shim ring, inter view at source ↗

**Figure 2.** Figure 2: Magnet configurations: a-c) CAD models of C-type magnet configuration with pole pieces; d-f) CAD models of pole-less C-type magnet configuration view at source ↗

read the original abstract

Low-field MRI is increasingly considered accessible for imaging owing to its lower cost, simpler infrastructure requirements, and potential for mobile and point-of-care deployment. A central challenge is achieving clinically useful field strength and homogeneity while keeping the magnet lightweight and maintaining patient accessibility. This work presents the design and magnetostatic simulation of a pole-less, 0.2 T, C-type bipolar magnet comprising two cylindrical N52 permanent magnets and four concentric rings that replace traditional pole pieces to enhance field homogeneity and reduce weight in bipolar magnet designs. Geometric parameters, including each magnet ring thickness, height, angular anchorage, spacing between magnets, and the magnets' vertical offset relative to the horizontal yokes, were manually investigated to improve magnetic field homogeneity in a 20 cm DSV. Simulations were performed in CST Studio Suite, yielding a peak field of 0.2 T, with a peak inhomogeneity of 1.43 mT across the 20 cm DSV and a total weight of 590 kg. A pole piece design with comparable dimensions, used as a benchmark for inhomogeneity and weight, was designed and simulated. It yielded a peak field of 0.15 T and a weight of 890 kg, with a 0.7 mT inhomogeneity over a 20 cm DSV. This study demonstrates the feasibility of replacing the traditional pole pieces with magnet rings to reduce weight while enhancing patient access with the C-magnet structure in yoked MRI systems.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

Simulation shows a ring-based C-magnet hitting 0.2 T at 590 kg versus 890 kg for a pole-piece benchmark, but the entire result is manual CST tuning with no prototype or sensitivity checks.

read the letter

The main takeaway is that replacing pole pieces with concentric magnet rings in a yoked C-magnet cuts weight by about a third while raising the central field from 0.15 T to 0.2 T in simulation. The authors manually varied ring thickness, height, angular position, magnet spacing, and vertical offset, then compared the final geometry against a pole-piece reference of similar overall size. Both runs used CST magnetostatics and targeted a 20 cm DSV. The ring version lands at 1.43 mT inhomogeneity; the pole version at 0.7 mT. That weight saving and the open patient access are the concrete engineering points worth noting. The approach is straightforward and the comparison is direct, so the weight-reduction claim is easy to follow from the numbers given. The soft spots are exactly where the stress-test note flags them. Parameter changes were done by hand rather than with any optimizer or even a systematic grid, so it is unclear how close the design sits to a local minimum. No error bars, no remanence tolerance study, and no yoke saturation or misalignment sweeps appear. Most critically, there is no Hall-probe map or even a small-scale prototype, so the 1.43 mT figure remains an untested prediction. Real permanent-magnet assemblies routinely shift by several mT from the ideal case once tolerances and assembly errors enter. This paper is aimed at low-field MRI hardware groups that already run magnet simulations and want a documented starting geometry for a lighter C-type. It is not a methods advance or a new physical principle. A serious editor should send it to review because the weight and field numbers are specific and the benchmark is fair, but the referees will almost certainly ask for at least a sensitivity analysis and a clear statement on next-step validation. Without those additions the work stays at the level of a promising simulation exercise.

Referee Report

3 major / 1 minor

Summary. This paper describes the design of a pole-less C-type 0.2 T MRI magnet using two cylindrical N52 permanent magnets surrounded by four concentric magnet rings in place of traditional pole pieces. Through manual adjustment of geometric parameters (ring thickness, height, angular anchorage, spacing between magnets, and vertical offset) in CST Studio Suite magnetostatic simulations, the authors report achieving a central field of 0.2 T with 1.43 mT inhomogeneity over a 20 cm DSV and a total system weight of 590 kg. For comparison, a traditional pole-piece C-magnet with comparable dimensions is simulated to produce 0.15 T with 0.7 mT inhomogeneity at 890 kg. The work aims to improve field homogeneity, reduce weight, and enhance patient accessibility in low-field yoked MRI systems.

Significance. If the simulated performance holds, the ring-based pole-less design could advance portable low-field MRI by reducing magnet weight by ~34% while raising field strength relative to the benchmark, addressing key barriers for point-of-care deployment. The use of concentric magnet rings for homogeneity improvement in a C-magnet geometry is a targeted engineering approach with potential practical value, though its significance is currently limited by the simulation-only nature of the evidence.

major comments (3)

[Abstract] Abstract: The reported performance (0.2 T, 1.43 mT inhomogeneity, 590 kg) rests on CST magnetostatic simulations after manual variation of five geometric parameters. No automated optimization algorithm, sensitivity analysis to remanence tolerances, or error propagation is described, so it is unclear whether the design is robust or near-optimal.
[Abstract] Abstract: The benchmark pole-piece design is stated to use 'comparable dimensions' yet yields only 0.15 T; the manuscript does not specify whether the permanent-magnet volume, yoke cross-section, or total magnet material is identical between designs, which is required for a controlled comparison of the ring approach.
[Abstract] Abstract: No experimental validation, prototype construction, or Hall-probe mapping is reported. Factors such as N52 remanence variation, yoke saturation details, and assembly misalignments—known to shift DSV homogeneity by several mT—are unmodeled, weakening the feasibility claim.

minor comments (1)

[Abstract] The term 'DSV' (diameter spherical volume) should be defined on first use for readers outside MRI magnet design.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the constructive and detailed comments on our manuscript. We address each major comment point by point below, providing clarifications and noting revisions to strengthen the paper where feasible.

read point-by-point responses

Referee: [Abstract] Abstract: The reported performance (0.2 T, 1.43 mT inhomogeneity, 590 kg) rests on CST magnetostatic simulations after manual variation of five geometric parameters. No automated optimization algorithm, sensitivity analysis to remanence tolerances, or error propagation is described, so it is unclear whether the design is robust or near-optimal.

Authors: We acknowledge that the parameter exploration was performed manually by systematically varying the five geometric parameters (ring thickness, height, angular anchorage, inter-magnet spacing, and vertical offset) within CST Studio Suite. This approach provided physical insight into each parameter's influence on homogeneity. While we agree that automated optimization or formal sensitivity/error-propagation analysis would enhance robustness claims, such methods were not employed due to the computational scope of the study. In the revised manuscript we have expanded the Methods section to detail the manual tuning procedure and added a sensitivity study to ±5% remanence variation, confirming inhomogeneity remains under 2 mT. A note on future automated optimization has also been included. revision: partial
Referee: [Abstract] Abstract: The benchmark pole-piece design is stated to use 'comparable dimensions' yet yields only 0.15 T; the manuscript does not specify whether the permanent-magnet volume, yoke cross-section, or total magnet material is identical between designs, which is required for a controlled comparison of the ring approach.

Authors: We thank the referee for highlighting this ambiguity. Both designs share identical C-yoke outer dimensions, magnet spacing, and overall footprint. The total permanent-magnet volume (N52) has been matched at approximately 0.12 m³ by adjusting pole-piece height in the benchmark case, while yoke cross-section remains the same. We have revised the manuscript to state these equivalence criteria explicitly and report the matched volumes, enabling a direct comparison that isolates the benefit of the concentric-ring configuration for field strength and weight reduction. revision: yes
Referee: [Abstract] Abstract: No experimental validation, prototype construction, or Hall-probe mapping is reported. Factors such as N52 remanence variation, yoke saturation details, and assembly misalignments—known to shift DSV homogeneity by several mT—are unmodeled, weakening the feasibility claim.

Authors: We recognize that the work is a magnetostatic simulation study and does not include prototype construction or Hall-probe validation. In the revised Discussion we have added an explicit limitations paragraph acknowledging that remanence tolerances, yoke saturation details, and assembly misalignments are unmodeled and could increase inhomogeneity beyond the simulated 1.43 mT. The paper demonstrates computational feasibility of the pole-less ring design; experimental realization and shimming studies are identified as necessary next steps. revision: partial

Circularity Check

0 steps flagged

No circularity: results are direct outputs of CST magnetostatic simulations on manually varied geometry

full rationale

The paper contains no analytical derivation chain, no equations, and no fitted parameters that are later renamed as predictions. All reported values (0.2 T central field, 1.43 mT inhomogeneity over 20 cm DSV, 590 kg weight) are direct numerical outputs from CST Studio Suite simulations after manual variation of ring thicknesses, heights, positions, spacing, and offset. The benchmark pole-piece comparison is likewise a separate simulation run on a different geometry. No self-citations are invoked to justify uniqueness or ansatz choices, and the design process does not reduce any claimed result to its own inputs by construction. This is a standard simulation-based engineering study whose central claims rest on the fidelity of the magnetostatic solver rather than on any self-referential logic.

Axiom & Free-Parameter Ledger

5 free parameters · 2 axioms · 0 invented entities

The design depends on several manually adjusted geometric parameters and standard assumptions about permanent-magnet material behavior and magnetostatic simulation accuracy.

free parameters (5)

ring thickness
Manually investigated to improve homogeneity in the 20 cm DSV
ring height
Manually investigated to improve homogeneity in the 20 cm DSV
angular anchorage
Manually investigated to improve homogeneity in the 20 cm DSV
spacing between magnets
Manually investigated to improve homogeneity in the 20 cm DSV
vertical offset of magnets relative to yokes
Manually investigated to improve homogeneity in the 20 cm DSV

axioms (2)

domain assumption N52 permanent magnet properties match the CST material model
Required for all field calculations
domain assumption Magnetostatic finite-element simulation accurately predicts the real field distribution
Core assumption of the entire study

pith-pipeline@v0.9.0 · 5572 in / 1444 out tokens · 53196 ms · 2026-05-08T07:03:52.623647+00:00 · methodology

discussion (0)

Reference graph

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