# Low-cost 300 mT Benchtop MRI Scanner and Custom MR Bioreactor for real-time multi-parametric assessment of 3D-bioprinted biological tissue constructs

Valernst Martial Gilmus, Yilbert Giménez, Tony Gerges, Jean-Lynce Gnanago, Philippe Lombard, Vincent Semet, Michel Cabrera, Christophe Marquette, Emma Petiot, Simon Auguste Lambert

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Valernst Martial Gilmus, Yilbert Giménez, Tony Gerges, Jean-Lynce Gnanago, Philippe Lombard, et al.. Low-cost 300 mT Benchtop MRI Scanner and Custom MR Bioreactor for real-time multi-parametric assessment of 3D-bioprinted biological tissue constructs. ESMRMB 2024 – 40th Annual Scientific Meeting, Oct 2024, Barcelone, Spain. 2024. [hal-05312609](https://hal.science/hal-05312609v1)

HAL Id: hal-05312609

https://hal.science/hal-05312609v1

Submitted on 13 Oct 2025

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Distributed under a Creative Commons Attribution 4.0 International License
## Introduction

Tissue engineering has made significant progress since the mid-1980s. New techniques, such as 3D bioprinting, have allowed for the creation of more complex and functional tissues. Today, tissue engineering is being used to develop a wide range of treatments for various conditions, from skin grafts and cartilage repair to bone regeneration¹,². So far, optical modalities have been the preferred method to inspect and characterize engineered tissues. However, with significant advances comes a need for more complex characterization tools as the parameters of interest multiply. Therefore, more versatile methods are crucial for evaluating advanced tissue-engineered constructs. These methods must be able to assess not only morphological but also functional and molecular information³. As a non-invasive and multi-parametric modality, MRI has long been identified as a strong candidate⁴,⁵. MRI enables real-time multi-parametric 3D characterization with a wide field of view (>cm) and no penetration depth limit. This gives access to a wide range of tissue development characteristics. However, primarily due to its cost and accessibility, it has yet to become the modality of choice for tissue-engineered construct characterization. Here, we propose a more accessible and cost-effective approach using a small 300 mT benchtop MRI and a custom-made MR Bioreactor with an integrated RF coil.

## Materials And Methods

### 300 mT Benchtop MRI

The MRI system used throughout this study was a custom-built 300 mT permanent magnet system from Pure Device (Fig.1) (130 kg / 310 x 400 x 270 mm) with a ¹H frequency of 13.03 MHz @ 29 °C and a maximum FOV of 40 x 40 x 60 mm. A shielded reference volume coil was provided by the MRI system manufacturer.

<figure><img src="image_3.png" /><figcaption>Figure 1: 300 mT low-cost portable Benchtop MRI from Pure Device (130 kg / 310 mm W 400 mm H 270 mm L)</figcaption></figure>

### Custom MR Bioreactor for 3D bioprinting

A dedicated bioreactor (Fig.2) (Ø 35 mm x 185 mm) was designed to fit inside the system and is comprised of a main cylindrical chamber (Ø 20 mm x 60 mm) to house the sample fed by its nutrient liquid through two inlets connected to an external peristaltic pump, and a piston for sterile tissue insertion with a flow distributor ("Sprinkler") to control the nutrient flow in the culture environment. All parts of the bioreactor were 3D printed using the autoclavable Formlabs High Temp V2 high precision resin.

<figure><img src="image_4.png" /><figcaption>Figure 2: A) CAD design exploded view of the MR-Bioreactor B) Picture of the final 3D printed bioreactor with integrated Ø 35 mm x 65 mm loop gap coil C) MR-Bioreactor Schematics illustrating the 3D-Bioprinting process and sterile tissue insertion.</figcaption></figure>

A T/R loop gap coil (Ø 34 mm x 65 mm) geometry was selected for maximum B1 field homogeneity and low susceptibility to coil detuning by sample coupling ⁶,⁷. The coil was directly deposited onto the outer surface of the bioreactor using a chemical copper plating method⁸ for an overall copper thickness >45. Two trimmer capacitors were added for precise tuning and matching. All of it was enclosed in a 59 x 180 x 220 mm 3D printed housing shielded using 25 µm thick cooper foil.

### Coil characterization and SNR Measurement

Quality factor measurements of both the 50Ω matched reference coil and the fabricated coil were performed on a Rohde and Schwarz ZNL6 – VNA and obtained from the frequency response of the reflection coefficient at the –3 dB.

$$Q = \frac{2\omega_0}{\Delta\omega}$$

To assess and compare the efficiency of both coils, SNR measurements were performed on a homogenous cylindrical saline phantom. A circular ROI incorporating most of the phantom while avoiding the edges was drawn over a uniform region of a coronal slice of the phantom to capture the signal, and four additional ROIs were drawn in the air regions, away from the phantom, to capture noise in areas where no object or structured noise at the corners of the image, to avoid phase-encoded ghosting or other artifacts that might propagate along the phase and frequency encoding directions.

<figure><img src="image_5.png" /><figcaption>Figure 3: Coronal slice of a 3D flash (TE=8 ms TR= 50 ms ) acquisition of a cylindrical (Ø 15 mm x 50 mm) homogenous saline phantom.</figcaption></figure>

$$SNR = 0.66 \times \frac{\text{mean Signal}}{\text{std Noise}}$$

### Preliminary results

#### Q- Factor and SNR Measurements

<table><thead><tr><td></td><td>Measured SNR</td><td>Estimated Q-Factor</td></tr></thead><tbody><tr><td>Reference Coil</td><td>34.6</td><td>132</td></tr><tr><td>MR-Bioreactor</td><td>48.2</td><td>150</td></tr></tbody></table>

#### First High-Resolution Images

A 3D-printed (Ø 20mm x 20mm) scaffold with 1 mm² square holes submerged in saline solution inside the perfused bioreactor was used as a test sample to obtain preliminary morphological results. Images were obtained using a 3D Spin Echo sequence (Repetition time (TR)=200ms, Echo time (TE)=20ms, 3 averages, Field-of-view (FOV)= 30 x 30 x 30 mm) for a 125 µm³ isotropic resolution.

<figure><img src="image_6.png" /><figcaption>Figure 4: A) Picture of 3D-printed (Ø 20mm x 20mm) scaffold with 1 mm² square holes. B) 3D Spin Echo (TR:200 ms, TE:20 ms, 3 averages, 125 µm³ Resolution, 2 h 43 min acquisition time) image of 3D-printed scaffold inside the perfused bioreactor. C) 3D reconstruction of 3D printed scaffold from image segmentation.</figcaption></figure>

### Discussion & Conclusions

The fabricated autoclavable perfused low-field MR bioreactor was bench characterized, and MRI tested using the 300 mT Pure Device portable benchtop MRI. The first high-resolution morphological images of plastic scaffold samples were obtained (Fig.4).

This work shows a definite first step towards the wider adoption of cost-effective MRI systems to characterize tissue-engineered constructs. The successful initial high-resolution morphological imaging of a 3D-printed scaffold validates the system's functionality. However, more work needs to be done to fully utilize the multiparametric aspect of MRI at low fields, such as the use of ADC for cellularity measurement as well as flow distribution measurements to obtain comparable results to those of higher field experiments ⁹,¹⁰.

### References

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4. Meadowcroft, M. D. et al. Direct magnetic resonance imaging of histological tissue samples at 3.0T. *Magn. Reson. Med.* **57**, 835–841 (2007).

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10. Gnanago, J.-L. & et al. (ISMRM 2022) 3D MRI characterization of 3D printed tumor tissue models using a plastronic MR-Bioreactor: Preliminary results. in Proceedings of the 30th International Society inMagnetic Resonance for Medecine Annual Meeting 2003. in (2022).

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