diff --git a/atlas/templates/atlas/case_display_block.html b/atlas/templates/atlas/case_display_block.html
index 884a4781..4449701f 100755
--- a/atlas/templates/atlas/case_display_block.html
+++ b/atlas/templates/atlas/case_display_block.html
@@ -1016,7 +1016,8 @@
         let dicomViewerLoaded = false;
         dicomDetails.addEventListener("toggle", function() {
             if (!dicomViewerLoaded && dicomDetails.open) {
-                window.mountDicomViewers();
+                // Use safe mount helper to avoid arbitrary timeouts
+                try { mountDicomViewersSafely(); } catch (e) { if (window.mountDicomViewers) try { window.mountDicomViewers(); } catch (er) { console.warn(er); } }
                 dicomViewerLoaded = true;
             }
         });
@@ -1162,25 +1163,23 @@
                         } else {
                             viewer_element_3d = null;
                         }
-                            // We have a slight delay to allow the viewer to load
-                        setTimeout(function () {
-                                // Then we load the annotation and viewport
-                            window.mountDicomViewers();
-                            if (load_3d) {
-                                console.log("loading 3d")
-
-                                    //setTimeout(function () {
-                                    //    console.log("loading 3d annotation")
-                                    //    importAnnotations_root(annotationjson3d)
-                                    //    importViewerState_root(viewerState);
-                                    //}, 1000);
-                            } else {
-                                console.log("not loading 3d")
+                            // Initialize viewer deterministically after injecting HTML
+                        (async function(){
+                            try {
+                                await mountDicomViewersSafely();
+                                if (load_3d) {
+                                    console.log("loading 3d");
+                                    // deferred 3D import can be handled here if needed
+                                } else {
+                                    console.log("not loading 3d");
+                                }
+                            } catch(e){
+                                console.warn('Viewer init error:', e);
                             }
-                        }, 200);
+                        })();
 
                         document.getElementById("reload-finding").addEventListener("click", function () {
-                            window.mountDicomViewers();
+                            mountDicomViewersSafely();
                         });
 
         // Initialize the DICOM viewer with the images and annotations
@@ -1201,6 +1200,36 @@
         const dsFullscreenModal = new bootstrap.Modal(document.getElementById("displaysetFullscreenModal"));
 
         // Loader functions: can be called directly on reload
+        // Helper: wait for mount function and mount the viewers safely
+        function waitForMountFn(timeout = 5000) {
+            if (window.mountDicomViewers) return Promise.resolve(window.mountDicomViewers);
+            return new Promise((resolve, reject) => {
+                const start = Date.now();
+                function poll() {
+                    if (window.mountDicomViewers) return resolve(window.mountDicomViewers);
+                    if (Date.now() - start > timeout) return reject(new Error('mountDicomViewers not available'));
+                    requestAnimationFrame(poll);
+                }
+                poll();
+            });
+        }
+
+        async function mountDicomViewersSafely(timeout = 5000) {
+            try {
+                // wait for layout to stabilise
+                await new Promise(r => requestAnimationFrame(() => requestAnimationFrame(r)));
+                const mountFn = await waitForMountFn(timeout);
+                try { mountFn(); } catch (e) { console.warn('mountDicomViewers failed', e); }
+                // allow any async render to settle then force a resize event
+                requestAnimationFrame(() => {
+                    try { window.dispatchEvent(new Event('resize')); } catch (e) {}
+                    if (typeof window.resizeDicomViewers === 'function') try { window.resizeDicomViewers(); } catch (e) {}
+                });
+            } catch (err) {
+                console.warn('Viewer initialization deferred/fallback:', err);
+            }
+        }
+
         async function loadDisplaysetModal(url, dsId) {
             if (!url && dsId) url = `/atlas/${dsId}/display_sets/modal`;
             if (!url) return;
@@ -1217,7 +1246,8 @@
                     }
                 } catch (e) { console.warn(e); }
                 try { setUrlParam('displayset', dsId); } catch (e) {}
-                setTimeout(function () { try { window.mountDicomViewers(); } catch (e) { console.warn('mountDicomViewers not available', e); } }, 500);
+                // Initialize viewer deterministically after injecting HTML
+                mountDicomViewersSafely();
                 dsModal.show();
             } catch (error) {
                 console.error('Error loading display set details:', error);
@@ -1249,7 +1279,8 @@
                 document.getElementById('displaysetFullscreenRight').innerHTML = tmp.innerHTML;
                 try { if (dsId) { setUrlParam('displayset', dsId); setUrlParam('displayset_full', '1'); } } catch (e) {}
                 dsFullscreenModal.show();
-                setTimeout(function () { try { window.mountDicomViewers(); } catch (e) { console.warn('mountDicomViewers not available for fullscreen', e); } }, 500);
+                // Ensure viewer is mounted and resized after moving into fullscreen
+                mountDicomViewersSafely();
             } catch (error) {
                 console.error('Error loading fullscreen display set:', error);
                 document.getElementById('displaysetFullscreenLeft').innerHTML = '<p style="color:#fff; padding:1rem;">Failed to load viewer</p>';
@@ -1266,11 +1297,12 @@
                 const resp = await fetch(url);
                 const html = await resp.text();
                 modalBody.innerHTML = html;
-                setTimeout(function () { try { window.mountDicomViewers(); } catch (e) { console.warn('mountDicomViewers not available', e); } }, 200);
+                // Ensure viewers mount after content injection
+                mountDicomViewersSafely();
                 try { setUrlParam('finding', findingId); } catch (e) {}
                 const modal = new bootstrap.Modal(document.getElementById('findingModal'));
                 modal.show();
-                document.getElementById('reload-finding')?.addEventListener('click', function () { window.mountDicomViewers(); });
+                document.getElementById('reload-finding')?.addEventListener('click', function () { mountDicomViewersSafely(); });
             } catch (e) {
                 console.error('Error loading finding details:', e);
                 modalBody.innerHTML = '<p>Failed to load finding details.</p>';
diff --git a/atlas/templates/atlas/case_displaysets.html b/atlas/templates/atlas/case_displaysets.html
index c12aa629..11fb2655 100755
--- a/atlas/templates/atlas/case_displaysets.html
+++ b/atlas/templates/atlas/case_displaysets.html
@@ -38,20 +38,48 @@
 {% block js %}
     <script>
         document.addEventListener("DOMContentLoaded", function () {
-            // Delay mounting slightly to ensure viewer assets and DOM are ready
-            setTimeout(function() { window.mountDicomViewers(); }, 500);
+            // Helper: wait for mount function and mount the viewers safely
+            function waitForMountFn(timeout = 5000) {
+                if (window.mountDicomViewers) return Promise.resolve(window.mountDicomViewers);
+                return new Promise((resolve, reject) => {
+                    const start = Date.now();
+                    function poll() {
+                        if (window.mountDicomViewers) return resolve(window.mountDicomViewers);
+                        if (Date.now() - start > timeout) return reject(new Error('mountDicomViewers not available'));
+                        requestAnimationFrame(poll);
+                    }
+                    poll();
+                });
+            }
+
+            async function mountDicomViewersSafely(timeout = 5000) {
+                try {
+                    await new Promise(r => requestAnimationFrame(() => requestAnimationFrame(r)));
+                    const mountFn = await waitForMountFn(timeout);
+                    try { mountFn(); } catch (e) { console.warn('mountDicomViewers failed', e); }
+                    requestAnimationFrame(() => { try { window.dispatchEvent(new Event('resize')); } catch (e) {} });
+                } catch (err) {
+                    console.warn('Viewer initialization deferred/fallback:', err);
+                }
+            }
+
+            // Initialize viewers deterministically
+            mountDicomViewersSafely();
 
 
             {% if selected_displayset %}
-                setTimeout(function() {
-                    importAnnotations_main_viewer({{ selected_displayset.annotations|safe }});
-                    importViewerState_main_viewer({{ selected_displayset.viewerstate|safe }});
-                    // Highlight the selected displayset row
-                    var selectedRow = document.getElementById("displayset-{{ selected_displayset.pk }}");
-                    if (selectedRow) {
-                        selectedRow.style.border = "2px solid #ffc107";
-                    }
-                }, 1000);
+                (async function(){
+                    try {
+                        await mountDicomViewersSafely();
+                        importAnnotations_main_viewer({{ selected_displayset.annotations|safe }});
+                        importViewerState_main_viewer({{ selected_displayset.viewerstate|safe }});
+                        // Highlight the selected displayset row
+                        var selectedRow = document.getElementById("displayset-{{ selected_displayset.pk }}");
+                        if (selectedRow) {
+                            selectedRow.style.border = "2px solid #ffc107";
+                        }
+                    } catch (e) { console.warn('failed to import selected displayset state', e); }
+                })();
 
                 {% if edit %}
                     var editButton = document.getElementById("displayset-{{ selected_displayset.pk }}-edit-btn");
diff --git a/atlas/templates/atlas/viewer_local.html b/atlas/templates/atlas/viewer_local.html
index 45ce1a3a..bc46503e 100644
--- a/atlas/templates/atlas/viewer_local.html
+++ b/atlas/templates/atlas/viewer_local.html
@@ -91,6 +91,29 @@
                 function hideResourceLocal(){ const disp=document.getElementById('resourceDisplay'); const inner=document.getElementById('resourceInner'); if(disp) disp.style.display='none'; if(inner) inner.innerHTML=''; }
                 (function(){ const disp=document.getElementById('resourceDisplay'); if(!disp) return; disp.addEventListener('click', function(e){ const close = e.target.closest && e.target.closest('#resourceClose'); if (close) hideResourceLocal(); }); })();
 
+                // Helper to safely mount the DICOM viewers (waits for bundle and layout)
+                function waitForMountFn(timeout = 5000) {
+                    if (window.mountDicomViewers) return Promise.resolve(window.mountDicomViewers);
+                    return new Promise((resolve, reject) => {
+                        const start = Date.now();
+                        function poll() {
+                            if (window.mountDicomViewers) return resolve(window.mountDicomViewers);
+                            if (Date.now() - start > timeout) return reject(new Error('mountDicomViewers not available'));
+                            requestAnimationFrame(poll);
+                        }
+                        poll();
+                    });
+                }
+
+                async function mountDicomViewersSafely(timeout = 5000) {
+                    try {
+                        await new Promise(r => requestAnimationFrame(() => requestAnimationFrame(r)));
+                        const mountFn = await waitForMountFn(timeout);
+                        try { mountFn(); } catch (e) { console.warn('mountDicomViewers failed', e); }
+                        requestAnimationFrame(() => { try { window.dispatchEvent(new Event('resize')); } catch (e) {} });
+                    } catch (err) { console.warn('Viewer initialization deferred/fallback:', err); }
+                }
+
                 bc.onmessage = (event) => {
                     // Ensure any existing overlay is closed on new load
                     try { hideResourceLocal(); } catch(_) {}
@@ -182,7 +205,7 @@
                         delete document.getElementById("root").dataset.annotationjson;
                     }
 
-                    window.mountDicomViewers();
+                    mountDicomViewersSafely();
                     bc.postMessage({"type": "open-complete-local"});
                 }
             };