MR Thermometry in Cerebrovascular Disease: Physiologic Basis, Hemodynamic Dependence, and a New Frontier in Stroke Imaging

Interactive Multi-Stage Robotic Positioner for Intra-Operative MRI-Guided Stereotactic Neurosurgery

Magnetic resonance imaging (MRI) demonstrates clear advantages over other imaging modalities in neurosurgery with its ability to delineate critical neurovascular structures and cancerous tissue in high-resolution 3D anatomical roadmaps. However, its application has been limited to interventions performed based on static pre/post-operative imaging, where errors accrue from stereotactic frame setup, image registration, and brain shift. To leverage the powerful intra-operative functions of MRI, e.g., instrument tracking, monitoring of physiological changes and tissue temperature in MRI-guided bilateral stereotactic neurosurgery, a multi-stage robotic positioner is proposed. The system positions cannula/needle instruments using a lightweight (203 g) and compact (Ø97 × 81 mm) skull-mounted structure that fits within most standard imaging head coils. With optimized design in soft robotics, the system operates in two stages: i) manual coarse adjustment performed interactively by the surgeon (workspace of ±30°), ii) automatic fine adjustment with precise (<0.2° orientation error), responsive (1.4 Hz bandwidth), and high-resolution (0.058°) soft robotic positioning. Orientation locking provides sufficient transmission stiffness (4.07 N/mm) for instrument advancement. The system's clinical workflow and accuracy is validated with lab-based (<0.8 mm) and MRI-based testing on skull phantoms (<1.7 mm) and a cadaver subject (<2.2 mm). Custom-made wireless omni-directional tracking markers facilitated robot registration under MRI.

MR Thermometry during Transcranial MR Imaging-Guided Focused Ultrasound Procedures: A Review

Interest in transcranial MR imaging-guided focused ultrasound procedures has recently grown. These incisionless procedures enable precise focal ablation of brain tissue using real-time monitoring by MR thermometry. This article will provide an updated review on clinically applicable technical underpinnings and considerations of proton resonance frequency MR thermometry, the most common clinically used MR thermometry sequence.

Continued Infarction Growth and Penumbral Consumption After Reperfusion in Vaccine-Naive Patients With COVID-19: A Case-Control Study

BACKGROUND. Neurologic sequelae of SARS-CoV-2 include potentially malignant cerebrovascular events arising from complex hemodynamic, hematologic, and inflammatory processes occurring in concert. OBJECTIVE. This study concerns the hypothesis that despite angiographic reperfusion COVID-19 promotes continued consumption of at-risk tissue volumes after acute ischemic stroke (AIS), yielding critical insights into prognostication and monitoring paradigms in vaccine-naive patients experiencing AIS. METHODS. This retrospective study compared 100 consecutive COVID-19 patients with AIS presenting between March 2020 and April 2021 with a contemporaneous cohort of 282 AIS patients without COVID-19. Reperfusion classes were dichotomized into positive (extended thrombolysis in cerebral ischemia [eTICI] score = 2c-3) and negative (eTICI score < 2c) groups. All patients underwent endovascular therapy after initial CT perfusion imaging (CTP) to document infarction core and total hypoperfusion volumes. RESULTS. Ten COVID-positive (mean age ± SD, 67 ± 12 years; seven men, three women) and 144 COVID-negative patients (mean age, 71 ± 16 years; 76 men, 68 women) undergoing endovascular reperfusion, with antecedent CTP and follow-up imaging, comprised the final dataset. Initial infarction core and total hypoperfusion volumes (mean ± SD) were 1.5 ± 18 mL and 85 ± 100 mL in COVID-negative patients and 30.5 ± 34 mL and 117 ± 80.5 mL in COVID-positive patients, respectively. Final infarction volumes were significantly larger in patients with COVID-19, with median volumes of 77.8 mL versus 18.2 mL among control patients (p = .01), as were normalized measures of infarction growth relative to baseline infarction volume (p = .05). In adjusted logistic parametric regression models, COVID positivity emerged as a significant predictor for continued infarct growth (OR, 5.10 [95% CI, 1.00-25.95]; p = .05). CONCLUSION. These findings support the potentially aggressive clinical course of cerebrovascular events in patients with COVID-19, suggesting greater infarction growth and ongoing consumption of at-risk tissues, even after angiographic reperfusion. CLINICAL IMPACT. SARS-CoV-2 infection may promote continued infarction progression despite angiographic reperfusion in vaccine-naive patients with large-vessel occlusion AIS. The findings carry potential implications for prognostication, treatment selection, and surveillance for infarction growth among revascularized patients in future waves of infection by novel viral strains.

Predicting brain temperature in humans using bioheat models: Progress and outlook

Brain temperature, regulated by the balance between blood circulation and metabolic heat generation, is an important parameter related to neural activity, cerebral hemodynamics, and neuroinflammation. A key challenge for integrating brain temperature into clinical practice is the lack of reliable and non-invasive brain thermometry. The recognized importance of brain temperature and thermoregulation in both health and disease, combined with limited availability of experimental methods, has motivated the development of computational thermal models using bioheat equations to predict brain temperature. In this mini-review, we describe progress and the current state-of-the-art in brain thermal modeling in humans and discuss potential avenues for clinical applications.

Magnetic Resonance Imaging for Guidance and Follow-up of Thoracic Needle Biopsies and Thermal Ablations

Magnetic resonance imaging (MRI) is used for the guidance and follow-up of percutaneous minimally invasive interventions in many body parts. In the thorax, computed tomography (CT) is currently the most used imaging modality for the guidance and follow-up of needle biopsies and thermal ablations. Compared with CT, MRI provides excellent soft tissue contrast, lacks ionizing radiation, and allows functional imaging. The role of MRI is limited in the thorax due to the low hydrogen proton density and many air-tissue interfaces of the lung, as well as respiratory and cardiac motion. Here, we review the current experience of MR-guided thoracic needle biopsies and of MR-guided thermal ablations targeting lesions in the lung, mediastinum, and the chest wall. We provide an overview of MR-compatible biopsy needles and ablation devices. We detail relevant MRI sequences and their relative advantages and disadvantages for procedural guidance, assessment of complications, and long-term follow-up. We compare the advantages and disadvantages of CT and MR for thoracic interventions and identify areas in need of improvement and additional research.

Portable, handheld, and affordable blood perfusion imager for screening of subsurface cancer in resource-limited settings

Existing procedures of screening subsurface cancers are either prohibitively resource-intensive and expensive or are unable to provide direct quantitative estimates of the relevant physiological parameters for accurate classification accommodating interpatient variabilities and overlapping clinical manifestations. Here, we introduce a handheld and inexpensive blood perfusion imager that provides a noninvasive in situ screening approach for distinguishing precancer, cancer, and normal scenarios by precise quantitative estimation of the localized blood circulation in the tissue over an unrestricted region of interest without any unwarranted noise in the data, augmented by machine learning–based classification. Clinical trials in minimally resourced settings have established the efficacy of the method in differentiating cancerous and precancerous stages of suspected oral abnormalities, as verified by gold-standard biopsy reports.

Precise information on localized variations in blood circulation holds the key for noninvasive diagnostics and therapeutic assessment of various forms of cancer. While thermal imaging by itself may provide significant insights on the combined implications of the relevant physiological parameters, viz. local blood perfusion and metabolic balance due to active tumors as well as the ambient conditions, knowledge of the tissue surface temperature alone may be somewhat inadequate in distinguishing between some ambiguous manifestations of precancer and cancerous lesions, resulting in compromise of the selectivity in detection. This, along with the lack of availability of a user-friendly and inexpensive portable device for thermal-image acquisition, blood perfusion mapping, and data integration acts as a deterrent against the emergence of an inexpensive, contact-free, and accurate in situ screening and diagnostic approach for cancer detection and management. Circumventing these constraints, here we report a portable noninvasive blood perfusion imager augmented with machine learning–based quantitative analytics for screening precancerous and cancerous traits in oral lesions, by probing the localized alterations in microcirculation. With a proven overall sensitivity >96.66% and specificity of 100% as compared to gold-standard biopsy-based tests, the method successfully classified oral cancer and precancer in a resource-limited clinical setting in a double-blinded patient trial and exhibited favorable predictive capabilities considering other complementary modes of medical image analysis as well. The method holds further potential to achieve contrast-free, accurate, and low-cost diagnosis of abnormal microvascular physiology and other clinically vulnerable conditions, when interpreted along with complementary clinically evidenced decision-making perspectives.

Monitoring and Prognostic Analysis of Severe Cerebrovascular Diseases Based on Multi-Scale Dynamic Brain Imaging

Severe cerebrovascular disease is an acute cerebrovascular event that causes severe neurological damage in patients, and is often accompanied by severe dysfunction of multiple systems such as breathing and circulation. Patients with severe cerebrovascular disease are in critical condition, have many complications, and are prone to deterioration of neurological function. Therefore, they need closer monitoring and treatment. The treatment strategy in the acute phase directly determines the prognosis of the patient. The case of this article selected 90 patients with severe cerebrovascular disease who were hospitalized in four wards of the Department of Neurology and the Department of Critical Care Medicine in a university hospital. The included cases were in accordance with the guidelines for the prevention and treatment of cerebrovascular diseases. Patients with cerebral infarction are given routine treatments such as improving cerebral circulation, protecting nutrient brain cells, dehydration, and anti-platelet; patients with cerebral hemorrhage are treated within the corresponding safe time window. We use Statistical Product and Service Solutions (SPSS) Statistics21 software to perform statistical analysis on the results. Based on the study of the feature extraction process of convolutional neural network, according to the hierarchical principle of convolutional neural network, a backbone neural network MF (Multi-Features)—Dense Net that can realize the fusion, and extraction of multi-scale features is designed. The network combines the characteristics of densely connected network and feature pyramid network structure, and combines strong feature extraction ability, high robustness and relatively small parameter amount. An end-to-end monitoring algorithm for severe cerebrovascular diseases based on MF-Dense Net is proposed. In the experiment, the algorithm showed high monitoring accuracy, and at the same time reached the speed of real-time monitoring on the experimental platform. An improved spatial pyramid pooling structure is designed to strengthen the network’s ability to merge and extract local features at the same level and at multiple scales, which can further improve the accuracy of algorithm monitoring by paying a small amount of additional computational cost. At the same time, a method is designed to strengthen the use of low-level features by improving the network structure, which improves the algorithm’s monitoring performance on small-scale severe cerebrovascular diseases. For patients with severe cerebrovascular disease in general, APACHEII1, APACHEII2, APACHEII3 and the trend of APACHEII score change are divided into high-risk group and low-risk group. The overall severe cerebrovascular disease, severe cerebral hemorrhage and severe cerebral infarction are analyzed, respectively. The differences are statistically significant.

Mild fever as a catalyst for consumption of the ischaemic penumbra despite endovascular reperfusion

Cerebrovascular ischaemia is potentiated by hyperthermia, and even mild temperature elevation has proved detrimental to ischaemic brain. Infarction progression following endovascular reperfusion relates to multiple patient-specific and procedural variables; however, the potential influence of mild systemic temperature fluctuations is not fully understood. This study aims to assess the relationship between systemic temperatures in the early aftermath of acute ischaemic stroke and the loss of at-risk penumbral tissues, hypothesizing consumption of the ischaemic penumbra as a function of systemic temperatures, irrespective of reperfusion status. A cross-sectional, retrospective evaluation of a single-institution, prospectively collected endovascular therapy registry was conducted. Patients with anterior circulation, large vessel occlusion acute ischaemic stroke who underwent initial CT perfusion, and in whom at least four-hourly systemic temperatures were recorded beginning from presentation and until the time of final imaging outcome were included. Initial CT perfusion core and penumbra volumes and final MRI infarction volumes were computed. Systemic temperature indices including temperature maxima were recorded, and pre-defined temperature thresholds varying between 37°C and 38°C were examined in unadjusted and adjusted regression models which included glucose, collateral status, reperfusion status, CT perfusion-to-reperfusion delay, general anaesthesia and antipyretic exposure. The primary outcome was the relative consumption of the penumbra, reflecting normalized growth of the at-risk tissue volume ≥10%. The final study population comprised 126 acute ischaemic stroke subjects (mean 63 ± 14.5 years, 63% women). The primary outcome of penumbra consumption ≥10% occurred in 51 (40.1%) subjects. No significant differences in baseline characteristics were present between groups, with the exception of presentation glucose (118 ± 26.6 without versus 143.1 ± 61.6 with penumbra consumption, P = 0.009). Significant differences in the likelihood of penumbra consumption relating to systemic temperature maxima were observed [37°C (interquartile range 36.5 − 37.5°C) without versus 37.5°C (interquartile range 36.8 − 38.2°C) with penumbra consumption, P = 0.001]. An increased likelihood of penumbra consumption was observed for temperature maxima in unadjusted (odds ratio 3.57, 95% confidence interval 1.65 − 7.75; P = 0.001) and adjusted (odds ratio 3.06, 95% confidence interval 1.33 − 7.06; P = 0.009) regression models. Significant differences in median penumbra consumption were present at a pre-defined temperature maxima threshold of 37.5°C [4.8 ml (interquartile range 0 − 11.5 ml) versus 21.1 ml (0 − 44.7 ml) for subjects not reaching or reaching the threshold, respectively, P = 0.007]. Mild fever may promote loss of the ischaemic penumbra irrespective of reperfusion, potentially influencing successful salvage of at-risk tissue volumes following acute ischaemic stroke.