AI Scientific Evidence - Healthcare IT

Emergency department triage: Artificial Intelligence’s gateway to radiology

The earliest adoption of artificial intelligence (AI) within clinical workflows has emerged within the emergency setting where it can manage priority for interpretation of imaging studies. In this triage role, AI does not commit to a diagnosis; rather it offers a binary decision as to whether the image contains a specific finding. The goal is to expedite the interpretation of the most critical cases, ultimately leading to improved patient outcomes.

Stroke workflow, primed for optimization
One clinical domain particularly suited to workflow optimization, due to its time critical nature, is acute stroke. Advances in treatment have resulted in continually shifting guidelines, adding complexity to the time pressured decisions. With several key imaging features involved in stroke triage, it lends itself to the current focus on narrow AI solutions.

Intracranial Hemorrhage (ICH) detection
ICH is a medical emergency and timely diagnosis is critical as nearly half of resulting mortalities occur within the first 24 hours. The speed of interpretation is dependent on the priority assigned to the scan request, which is a particular risk when symptoms can be vague. Automated ICH detection, as implemented by Canon Medical Systems’ Stroke CT Package, can address this problem by automatically detecting ICH and pushing the results to the neurointerventionalist. A case example is shown in Figure 1.

Performance of this algorithm, assessed in a validation cohort of 200 ICH positive and 102 non-ICH patients, yielded the following results (Table 1): a sensitivity of 0.93, specificity of 0.93, Positive Predictive Value (PPV) of 0.85 and Negative Predictive Value (NPV) of 0.98. Of note, where the algorithm performance is challenged is in cases of small volume hemorrhages. The author notes that ensemble methods using multimodal data may be used to address this limitation in the future.

All (n = 258)Small ICH (n = 93)Medium ICH (n = 117)Large ICH (n = 48)
ICH volume (mL)17.2 ± 2.71.7 ± 0.313.2 ± 1.257.3 ± 6.1
Accuracy0.94 ± 0.010.94 ± 0.020.93 ± 0.020.95 ± 0.02
Sensitivity0.93 ± 0.030.89 ± 0.050.94 ± 0.040.99 ± 0.01
Specificity0.93 ± 0.010.94 ± 0.020.92 ± 0.020.92 ± 0.04
Positive predictive value0.85 ± 0.020.81 ± 0.050.86 ± 0.030.91 ± 0.04
Negative predictive value0.98 ± 0.010.98 ± 0.010.98 ± 0.010.99 ± 0.01
F1 score0.86 ± 0.030.81 ± 0.060.87 ± 0.040.94 ± 0.02
Matthews correlation coefficient0.87 ± 0.020.83 ± 0.040.87 ± 0.030.90 ± 0.04
Proper triage as ICH positive, % (n)95 (245)92.5 (86)94.9 (111)100.0 (48)
Table 1. 95% Confidence Intervals for ICH volume, accuracy, sensitivity, specificity, positive predictive value, negative predictive value, F1 score, and Matthews correlation metrics corresponding to the ICH detection algorithm for all, small (≤5 mL), medium (>5 and <30 mL), and large (≥30 mL) ICHs. The percentage of times the algorithm correctly detects an ICH is also indicated.
Figure 1: Stroke CT Package was used to detect and segment the hemorrhage regions from the non contrast computed tomography (NCCT) image. The top left image shows an axial slice from the NCCT volume which is processed by the software. The boundary of the detected hemorrhagic region is shown in top right for the same axial slice*. Automatic detection is performed throughout entire volume. Bottom left image shows the segmented hemorrhage in purple (using Vitrea Advanced Visualization), with a manually adjustable outline in red. The bottom right image displays an volume view of the segmented hemorrhage (using Vitrea Advanced Visualization) along with the automated volume measurement and mean Hounsfield unit (HU).

* Not available in all geographies.

Reference
Rava et al. | Assessment of an Artificial Intelligence Algorithm for Detection of Intracranial Hemorrhage | World Neurosurgery (2021)
https://pubmed.ncbi.nlm.nih.gov/33684578/
Large Vessel Occlusion (LVO) detection
With the introduction of endovascular clot retrieval to routine clinical workflows, the identification of those patients who would benefit from the treatment quickly became top priority in stroke workflows. Implementing the automated detection of large vessel occlusions (LVO) in CTA, as provided by Canon Medical Systems’ Stroke CT Package, addresses this triage need.

The performance of this LVO detection solution was assessed in a cohort of 202 acute ischemic patients, 100 of whom had an occlusion within the Internal Carotid Artery (ICA), M1 or M2 regions of the Middle Cerebral Artery (MCA) and 102 patients with no occlusion. Analysis including all patients produced the following metrics (Table 1): a sensitivity of 0.73, specificity of 0.98, PPV of 0.99 and NPV of 0.64. As with ICH detection, it seems size matters. As the occlusions become more distal, within the MCA M2 region, they decrease in size and a drop off in performance is seen, with sensitivity falling to 0.5. With any such automated detection task there is a trade off in sensitivity versus specificity, however in this clinical scenario this algorithm, for all vessel locations, may benefit from further weighting to improve sensitivity. Figure 1 shows a clinical case example with detected LVO.

These triage applications of narrow AI have become a reality within acute stroke workflows and now the discussion of the effectiveness of these solutions is coming to the fore. It’s clear that further improvement is needed to address the challenges around the smaller, more subtle examples of pathologies, which will be tackled by additional training examples and techniques such as ensemble learning.

All (n = 303)ICA (n = 160)MCA M1 (n = 183)MCA M2 (n = 162)
Accuracy0.810.950.890.80
Sensitivity0.730.900.770.51
Specifi city0.980.980.980.98
Positive predictive value0.990.960.970.94
Negative predictive value0.640.940.840.77
F1 score0.840.930.860.66
Matthews correlation coefficient0.670.890.780.59
Table 1. Accuracy, sensitivity, specificity, positive predictive value, negative predictive value, F1 score and Matthews correlation metrics corresponding to the LVO detection algorithm for all and each occlusion site.
Figure 1: Correctly predicted large vessel occlusion (LVO) in case with right middle cerebral artery (MCA) occlusion. Top row shows coronal and axial views of the correctly labeled LVO, as indicated by the red box*. Bottom row shows the same case with 2D MIP subtraction and 3D MIP subtraction (right) where you can visualize the lack of contrast distal to the occlusion.

* Not available in all geographies.

Reference
Rava et al. | Validation of an Artificial Intelligence Driven Large Vessel Occlusion Detection Algorithm for Acute Ischemic Stroke Patients | The Neuroradiology Journal (2021)
https://pubmed.ncbi.nlm.nih.gov/33657922/

Healthcare Information Technology

  • Rava et al. | Assessment of an Artificial Intelligence Algorithm for Detection of Intracranial Hemorrhage | World Neurosurgery (2021)
    https://pubmed.ncbi.nlm.nih.gov/33684578/
  • Rava et al. | Validation of an Artificial Intelligence Driven Large Vessel Occlusion Detection Algorithm for Acute Ischemic Stroke Patients | The Neuroradiology Journal (2021)
    https://pubmed.ncbi.nlm.nih.gov/33657922/
  • Rava et al. | Assessment of a Bayesian Vitrea CT Perfusion Analysis to Predict Final Infarct and Penumbra Volumes in Patients with Acute Ischemic Stroke: A Comparison with RAPID | American Journal of Neuroradiology (AJNR) (2020)
    https://pubmed.ncbi.nlm.nih.gov/31948951/
  • Rava et al. | Assessment of computed tomography perfusion software in predicting spatial location and volume of infarct in acute ischemic stroke patients: a comparison of Sphere, Vitrea, and RAPID | Journal of NeuroInterventional Surgery (JNIS) (2020)
    https://pubmed.ncbi.nlm.nih.gov/32457224/
  • Rava et al. | Enhancing performance of a computed tomography perfusion software for improved prediction of final infarct volume in acute ischemic stroke patients | The Neuroradiology Journal (2021)
    https://pubmed.ncbi.nlm.nih.gov/33472519/
  • Ohno et al. | Machine learning for lung CT texture analysis: Improvement of inter-observer agreement for radiological finding classification in patients with pulmonary diseases | Eur J Radiol. (2021)
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X-Ray

Nuclear Medicine and Molecular Imaging

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