{
  "abstract": "Purpose: To demonstrate how diffusion blurs the longitudinal magnetization in steady-state gradient-echo imaging, quantify resolution dependence on flip angle and repetition time, and the effects on relaxometry at microscopic resolution. Methods: Diffusion was incorporated into the Bloch-Torrey equation in $k$ space to determine how the point spread function (PSF) of $T_1$-weighted spoiled gradient-echo images varies with flip angle. Theoretical predictions were validated numerically and extended to b-SSFP. Results: Diffusion acts as a low-pass filter whose width depends on the diffusion rate ($D$), repetition time (TR), $T_1$ and flip angle ($α$). The blurring length spans from $\\sqrt{D \\cdot \\mathrm{TR}/2}$ at large $α$ to $\\sqrt{D T_1}$ as $α\\rightarrow 0$, equaling $\\sqrt{D T_1/2}$ at the Ernst angle. Consequently, multi-angle acquisitions have mismatched resolution (PSF widths of 39 $μ$m at $α= 10^\\circ$ versus 11 $μ$m at $α= 80^\\circ$ for TR = 50 ms). For the flip-angle pair optimizing variable-flip-angle $T_1$ mapping, the effective resolutions differ by a factor of 2.4. In simulated DESPOT1 maps the $R_1$ of a 30 $μ$m feature is reduced to 1.80 s$^{-1}$ (true value 2.00 s$^{-1}$). In b-SSFP, blurring depends on $T_1$, $T_2$, and $α$ but is independent of TR, with a minimum of $\\sqrt{D T_2}$. Conclusion: The PSF of a steady-state sequence depends on the flip angle and $T_1$. Combining images acquired at different flip angles implicitly assumes identical spatial resolution, but that is not valid at microscopic scales, affecting the accuracy of quantitative relaxometry. The theory identifies a new limitation on the ultimate resolution of MRI set by diffusion.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.02132",
  "author_total": 2,
  "authors": [
    {
      "name": "Bibek Dhakal"
    },
    {
      "name": "John C. Gore"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/f8n3fz1fakeym.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.02132",
  "fulltext_url": null,
  "id": "f8n3fz1fakeym",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.02132",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "physics.med-ph"
    ],
    [
      "openalex",
      "2741|Advanced MRI Techniques and Applications"
    ]
  ],
  "openalex": "W7219155413",
  "pdf_url": "https://arxiv.org/pdf/2610.02132",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-02",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/f8n3fz1fakeym.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:26:45Z",
      "native_id": "2610.02132",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.02132"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:physics.med-ph",
      "subfield": "biological-medical"
    }
  ],
  "title": "Diffusion broadening of the point spread function in steady-state MRI",
  "title_text": "Diffusion broadening of the point spread function in steady-state MRI",
  "type": "preprint",
  "updated_at": "2026-10-30T12:26:45Z",
  "url": "https://research.draconitic.com/paper/f8n3fz1fakeym",
  "venue": "arXiv",
  "versions": []
}