[論文レビュー] Time-Resolved Multi-Spectral X-ray Computed Tomography of Cryoprotectant Diffusion Into Biomimetic Material

Alaa M. Ali, Jason T. Parker+5 more|arXiv (Cornell University)|Jan 29, 2026

Reproductive Biology and Fertility被引用数 0

ひとこと要約

The paper introduces time-resolved multi-spectral X-ray CT (MSCT) with an energy-bin optimization to decompose multi-component cryoprotectant cocktails as they diffuse into a tissue-mimicking hydrogel, enabling component-resolved, contrast-agent-free measurements and revealing heterogeneous diffusion.

ABSTRACT

Cryopreservation via vitrification requires loading cryoprotective cocktails. Insufficient loading may lead to freezing, precluding successful recovery; overloading is toxic. Yet, existing in situ measurements of cryoprotectant permeation remain largely unvalidated and do not resolve individual cryoprotectant concentrations. We introduce multi-spectral X-ray computed tomography (MSCT) to noninvasively quantify the spatiotemporal distribution of cryoprotectants diffusing into a tissue mimicking phantom. A developed photon-energy bin selection algorithm achieves sensitivity to low contrast cryoprotectants without contrast agents or fluorescence edges. The technique is validated with a dimethyl sulfoxide, glycerol, and water solution, resolving cryoprotectant volume fractions to within 5% accuracy. We observe heterogeneous diffusion of the cryoprotectants into the tissue mimicking hydrogel, a phenomenon not observable with conventional techniques. MSCT improves upon existing X ray CT methods because it is not underdetermined for multicomponent solutions and does not implicitly assume homogeneous diffusion. These advancements enable the systematic development of cryoprotectant loading protocols and provide diagnostics to assess vitrifiability before cryopreservation.

研究の動機と目的

• Develop a non-invasive MSCT method to quantify spatiotemporal distributions of multi-component cryoprotectants (CPAs) without contrast agents.
• Validate MSCT by decomposing a DMSO–glycerol–water solution and achieving accurate component volume fractions (within 5%).
• Demonstrate heterogeneous CPA diffusion into a tissue-mimicking hydrogel and compare MSCT results to conventional energy-integrating CT.
• Provide diagnostics to inform rational CPA loading protocols for vitrification and discuss broader applicability to multi-component diffusion systems.

提案手法

• Use a polychromatic X-ray source with an energy-resolving photon counting detector (ME3) capable of up to 128 energy bins.
• Develop and apply an energy-bin selection algorithm (balanced strategy) to maximize multi-component contrast while preserving photon flux.
• Decompose the voxel-wise attenuation into component volume fractions using a regularized least-squares approach (Aφ = R, with φ summing to 1 and 0≤φ≤1; regularization with parameter λ).
• Validate the method on binary/ternary CPA solutions to quantify accuracy (mean errors and comparison to true fractions).
• Apply MSCT to diffusion experiments in a tissue-mimicking hydrogel to obtain time-resolved, component-resolved concentration maps without contrast agents.

Figure 1 : (a) The X-ray source is a tungsten-target YXLON FXE225.99 X-ray source with the directional head installed. The source emits a polychromatic cone beam with a 15° angle. The detector in this study is a Detection Technologies X-Card ME3 line detector capable of up to 128 photon energy bins.

実験結果

リサーチクエスチョン

• RQ1 MSCTは対比剤を使用せずに多成分CPA溶液を個々の成分に分解できるか？
• RQ2 三元溶液における各CPA成分の真の体積分率をMSCTはどれだけ正確に回復できるか？
• RQ3 CPAsはハイドロゲル内で不均一に拡散するか、そしてこれが従来のCTと比較して拡散測定の解釈にどのように影響するか？
• RQ4 エネルギー-bin最適化戦略は、検証シナリオ全体で最大フラックス戦略・最大コントラスト戦略と比較して分解性能を向上させるか？

主な発見

• MSCTの三成分CPA溶液の分解は5%以内の誤差を達成（例：溶液1でDMSOの平均誤差1.9%、グリセロール0.6%、水2.5%； 溶液2で0.8%、3.5%、2.7%）。
• バランス型エネルギー-bin戦略は、検証された溶液全体で成分分解において最大フラックス戦略および最大コントラスト戦略を上回った。
• ハイドロゲル拡散実験は不均一拡散を示し、グリセロールはDMSOおよび水より速く拡散し、CPAsが拡散するにつれて濃度が低下し、ゲル内部で分布が非一様である。
• MSCTは結合溶質の減衰が一定でないことを示し、エネルギー統合CTでは捉えられない不均一なCPA分布を示す。
• 拡散スキャン（1回あたり15分、合計約1時間）は、CPA灌流およびガラス化プロトコルを知らせるのに適した時系列・成分分解マップを可能にする。

(a) Solution 1