span>
<span id="cb7-3"><a href="#cb7-3" tabindex="-1"></a></span>
<span id="cb7-4"><a href="#cb7-4" tabindex="-1"></a><span class="co"># Convert ROI to sparse volume</span></span>
<span id="cb7-5"><a href="#cb7-5" tabindex="-1"></a>sparse_roi <span class="ot">&lt;-</span> <span class="fu">as.sparse</span>(roi)</span>
<span id="cb7-6"><a href="#cb7-6" tabindex="-1"></a></span>
<span id="cb7-7"><a href="#cb7-7" tabindex="-1"></a><span class="co"># Compare memory usage (convert original ROI to dense for baseli