scholarly journals Ablation dynamics of subsequent thermal doses delivered to previously heat-damaged tissue during magnetic resonance–guided laser-induced thermal therapy

2019 ◽  
Vol 131 (6) ◽  
pp. 1958-1965 ◽  
Author(s):  
Sean M. Munier ◽  
Eric L. Hargreaves ◽  
Nitesh V. Patel ◽  
Shabbar F. Danish
Keyword(s):  
Magnetic Resonance ◽  
Thermal Damage ◽  
Total Duration ◽  
Ablation Rate ◽  
Thermal Therapy ◽  
Similar Amount ◽  
Thermal Dose ◽  
Surgical Indications ◽  
Maximum Area ◽  
Mri Guided

OBJECTIVEIntraoperative dynamics of magnetic resonance–guided laser-induced thermal therapy (MRgLITT) have been previously characterized for ablations of naive tissue. However, most treatment sessions require the delivery of multiple doses, and little is known about the ablation dynamics when additional doses are applied to heat-damaged tissue. This study investigated the differences in ablation dynamics between naive versus damaged tissue.METHODSThe authors examined 168 ablations from 60 patients across various surgical indications. All ablations were performed using the Visualase MRI-guided laser ablation system (Medtronic), which employs a 980-nm diffusing tip diode laser. Cases with multiple topographically overlapping doses with constant power were selected for this study. Single-dose intraoperative thermal damage was used to calculate ablation rate based on the thermal damage estimate (TDE) of the maximum area of ablation achieved (TDEmax) and the total duration of ablation (tmax). We compared ablation rates of naive undamaged tissue and damaged tissue exposed to subsequent thermal doses following an initial ablation.RESULTSTDEmax was significantly decreased in subsequent ablations compared to the preceding ablation (initial ablation 227.8 ± 17.7 mm2, second ablation 164.1 ± 21.5 mm2, third ablation 124.3 ± 11.2 mm2; p = < 0.001). The ablation rate of subsequent thermal doses delivered to previously damaged tissue was significantly decreased compared to the ablation rate of naive tissue (initial ablation 2.703 mm2/sec; second ablation 1.559 mm2/sec; third ablation 1.237 mm2/sec; fourth ablation 1.076 mm/sec; p = < 0.001). A negative correlation was found between TDEmax and percentage of overlap in a subsequent ablation with previously damaged tissue (r = −0.164; p < 0.02).CONCLUSIONSAblation of previously ablated tissue results in a reduced ablation rate and reduced TDEmax. Additionally, each successive thermal dose in a series of sequential ablations results in a decreased ablation rate relative to that of the preceding ablation. In the absence of a change in power, operators should anticipate a possible reduction in TDE when ablating partially damaged tissue for a similar amount of time compared to the preceding ablation.

Characterization of Magnetic Resonance Thermal Imaging Signal Artifact During Magnetic Resonance Guided Laser-Induced Thermal Therapy

2020 ◽  
Vol 19 (5) ◽  
pp. 619-624
Author(s):  
Sean M Munier ◽  
Allison S Liang ◽  
Akshay N Desai ◽  
Jose K James ◽  
Shabbar F Danish
Keyword(s):  
Magnetic Resonance ◽  
Patient Outcomes ◽  
Thermal Imaging ◽  
Thermal Damage ◽  
Invasive Procedure ◽  
Thermal Therapy ◽  
Surgical Indications ◽  
Ablation Procedure ◽  
Future Studies

Abstract BACKGROUND Magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) is a minimally invasive procedure that utilizes intraoperative magnetic resonance thermal imaging (MRTI) to generate a thermal damage estimate (TDE) of the ablative area. In select cases, the MRTI contains a signal artifact or defect that distorts the ablative region. No study has attempted to characterize this artifact. OBJECTIVE To characterize MRTI signal the artifact in select cases to better understand its potential relevance and impact on the ablation procedure. METHODS All ablations were performed using the Visualase magnetic resonance imaging-guided laser ablation system (Medtronic). Patients were included if the MRTI contained signal artifact that distorted the ablative region during the first thermal dose delivered. Ablation artifact was quantified using MATLAB version R2018a (Mathworks Inc, Natick, Massachusetts). RESULTS A total of 116 patients undergoing MRgLITT for various surgical indications were examined. MRTI artifact was observed in 37.0% of cases overall. Incidence of artifact was greater at higher powers (P &lt; .001) and with longer ablation times (P = .024), though artifact size did not correlate with laser power or ablation duration. CONCLUSION MRTI signal artifact is common during LITT. Higher powers and longer ablation times result in greater incidence of ablation artifact, though artifact size is not correlated with power or duration. Future studies should aim to evaluate effects of artifact on postoperative imaging and, most notably, patient outcomes.

Magnetic Resonance Imaging Conditionally Safe Neurostimulation Leads

Neurosurgery ◽  
2013 ◽  
Vol 74 (2) ◽  
pp. 215-225 ◽  
Author(s):  
Robert J. Coffey ◽  
Ron Kalin ◽  
James M. Olsen
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Animal Studies ◽  
Thermal Damage ◽  
Neurological Injury ◽  
Cns Injury ◽  
Thermal Dose ◽  
Rf Heating ◽  
Resonance Imaging ◽  
Increased Risk

Abstract BACKGROUND: Magnetic resonance imaging (MRI) is preferred for imaging the central nervous system (CNS). An important hazard for neurostimulation patients is heating at the electrode interface induced, for example, by 64-MHz radiofrequency (RF) magnetic fields of a 1.5T scanner. OBJECTIVE: We performed studies to define the thermal dose (time and temperature) that would not cause symptomatic neurological injury. METHODS: Approaches included animal studies where leads with temperature probes were implanted in the brain or spine of sheep and exposed to RF-induced temperatures of 37°C to 49°C for 30 minutes. Histopathological examinations were performed 7 days after recovery. We also reviewed the threshold for RF lesions in the CNS, and for CNS injury from cancer hyperthermia. Cumulative equivalent minutes at 43°C was used to normalize the data to exposure times and temperatures expected during MRI. RESULTS: Deep brain and spinal RF heating up to 43°C for 30 minutes produced indistinguishable effects compared with 37°C controls. Exposures greater than 43°C for 30 minutes produced temperature-dependent, localized thermal damage. These results are consistent with limits on hyperthermia exposure to 41.8°C for 60 minutes in patients who have cancer and with the reversibility of low-temperature and short-duration trial heating during RF lesion procedures. CONCLUSION: A safe temperature for induced lead heating is 43°C for 30 minutes. MRI-related RF heating above 43°C or longer than 30 minutes may be associated with increased risk of clinically evident thermal damage to neural structures immediately surrounding implanted leads. The establishment of a thermal dose limit is a first step toward making specific neurostimulation systems conditionally safe during MRI procedures.

scholarly journals NIMG-68. MATHEMATICAL MODELING OF THERMAL DAMAGE ESTIMATE VOLUMES IN MAGNETIC RESONANCE-GUIDED LASER INTERSTITIAL THERMAL THERAPY

2020 ◽  
Vol 22 (Supplement_2) ◽  
pp. ii163-ii163
Author(s):  
Allison Liang ◽  
Sean Munier ◽  
Shabbar Danish
Keyword(s):  
Magnetic Resonance ◽  
Thermal Damage ◽  
Invasive Procedure ◽  
Thermal Therapy ◽  
Definite Integral ◽  
Strongly Correlated ◽  
Dual Plane ◽  
Laser Interstitial Thermal Therapy ◽  
Integral Methods ◽  
Ablation Volume

Abstract BACKGROUND Magnetic resonance-guided laser interstitial thermal therapy is a minimally invasive procedure that produces real-time thermal damage estimates of ablation (TDE). Orthogonal TDE-MRI slices provides an opportunity to mathematically estimate ablation volume. OBJECTIVE To mathematically model TDE volumes and validate with post-24 hours MRI ablation volumes. METHODS Ablations were performed with the Visualase Laser Ablation System (Medtronic). Using ellipsoidal parameters determined for dual-TDEs from orthogonal MRI planes, TDE volumes were calculated by two definite integral methods (A and B) implemented in Matlab (MathWorks). Post 24-hours MRI ablative volumes were measured in OsiriX (Pixmeo) by two-blinded raters and compared to TDE volumes via paired t-tests and Pearson’s correlations. RESULTS Twenty-two ablations for 20 patients with various intracranial pathologies were included. Average TDE volumes calculated with Method A was 3.44 ± 1.96 cm3 and with Method B was 4.83 ± 1.53 cm3. Method A TDE volumes were significantly different than post-24 hours volumes (P &lt; 0.001). Method B TDE volumes were not significantly different than post-24 hours volumes (P = 0.39) and strongly correlated with each other (r = 0.85, R2 = 0.72, P &lt; 0.0001). A total of 8/22 (36%) method A versus 17/22 (77%) method B TDE volumes were within 25% of the post 24-hours ablative volume. CONCLUSION We present the first iteration of a viable mathematical method that integrates dual-plane TDEs to calculate volumes resembling 24 hours post-operative volumes. Future iterations of our algorithm will need to determine additional calculated variables that improve the performance of volumetric calculations.

scholarly journals A Novel Computational Approach in MATLAB to Characterize Thermal Damage Estimate in Magnetic Resonance-Guided Laser Interstitial Thermal Therapy

Neurosurgery ◽  
2019 ◽  
Vol 66 (Supplement_1) ◽  
Author(s):  
Allison Liang ◽  
Sean Munier ◽  
Shabbar F Danish
Keyword(s):  
Magnetic Resonance ◽  
Thermal Damage ◽  
Invasive Procedure ◽  
Thermal Therapy ◽  
Value Differences ◽  
Laser Interstitial Thermal Therapy ◽  
Large Sets ◽  
The Mean ◽  
Mean Differences ◽  
Student’S T

Abstract INTRODUCTION Magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) is a minimally invasive procedure that produces real-time thermal damage estimate (TDE) of the ablative area. Measurements of TDE by hand across a full ablation can be time-consuming, and currently, no reliable image analysis exists for measuring TDE dimensions efficiently. METHODS Ablations were performed with the Visualase MRI-Guided Laser Ablation System (Medtronic). Selection criteria included single-laser catheter use and available ablation data in 2 planes. Central TDE lengths and widths postsingle ablation dose were calculated using our developed MATLAB algorithm and compared to manual measurements by 2 raters. The Bland-Altman model and Student's t-tests were used to characterize value differences between the 2 methods. RESULTS A total of 42 TDE images across 21 patients were included. The mean differences in TDE length for rater 1 vs algorithm, rater 2 vs algorithm, and rater 1 vs rater 2 were −0.12 mm (SEM = 0.18), −0.54 mm (SEM = 0.17), and 0.42 mm (SEM = 0.17), respectively. The mean difference in TDE width for rater 1 vs algorithm, rater 2 vs algorithm, and rater 1 vs rater 2 were 0.45 mm (SEM = 0.16), −0.46 mm (SEM = 0.16), and 0.91 mm (SEM = 0.12), respectively. For both lengths and widths, student's t-tests show no significance differences across rater 1 and rater 2 vs algorithm (P > .1) and between raters (P > .05). CONCLUSION Our iterative algorithm provides a reliable method for calculating TDE dimensions. Compared to manual measurements, the differences in TDE length and width are negligible. This computational tool allows for measurement of TDE for large sets of MRgLITT data within minutes.

Does the Thermal Damage Estimate Correlate With the Magnetic Resonance Imaging Predicted Ablation Size After Laser Interstitial Thermal Therapy?

2017 ◽  
Vol 15 (2) ◽  
pp. 179-183 ◽  
Author(s):  
Nitesh V Patel ◽  
Kiersten Frenchu ◽  
Shabbar F Danish
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Thermal Damage ◽  
Pearson Correlation ◽  
Thermal Therapy ◽  
Statistical Testing ◽  
Resonance Imaging ◽  
Ablation Area ◽  
Wide Range ◽  
Significant Difference

Abstract BACKGROUND Magnetic resonance guided laser induced thermal therapy (LITT) is a minimally invasive method to treat a wide range of intracranial pathologies. The Arrhenius model is used to generate a thermal damage estimate (TDE) predicting ablation extent. OBJECTIVE Evaluation and correlation of the TDE to magnetic resonance imaging (MRI)-estimated ablation extent in human cases. METHODS The Medtronic Visualase system (Medtronic Inc, Dublin, Ireland) was utilized. Postablation axial T1-contrast enhanced images were acquired and intraoperative TDE image was obtained from the Visualase console. OsiriX DICOM Viewer (Pixmeo Inc, Bernex, Switzerland) was utilized to calculate cross-sectional area on MRI. ImageJ (National Institutes of Health, Bethesda, Maryland) was utilized for TDE area. Two blinded raters performed all measures. Statistical testing included Pearson correlation and the Student's t-test. RESULTS Twenty-two cases including tumor and epilepsy were evaluated. Average MRI predicted tumor ablation area was 4.72 ± 2.22 cm2 and average predicted epilepsy ablation area was 4.12 ± 1.89 cm2. Average tumor TDE was 4.02 ± 1.95 cm2 and average epilepsy TDE was 4.36 ± 2.21 cm2. Rater 1’s ablation areas and TDEs correlated with r = 0.89 (P &lt; .0001) and no significant difference (P &gt; .5). Rater 2’s ablation areas and TDEs correlated with r = 0.91 (P &lt; .0001) and no significant difference (P &gt; .7). Rater 1 vs Rater 2 showed a strong correlation for TDE (r = 0.98, P &lt; .000001) and ablation area (r = 0.96, P &lt; .0001) and no significant difference (P &gt; .5). CONCLUSION The TDE is an accurate and reliable measure of ablated area in LITT in human cases as assessed on postoperative MRI. Future studies should be larger and assess reliability of the TDE when multiple lasers and planes are used.

scholarly journals A new CEM₄₃ thermal dose model based on Vogel-Tammann-Fulcher behaviour in thermal damage processes

2021 ◽  
Author(s):  
Hisham Assi
Keyword(s):  
High Temperature ◽  
Thermal Damage ◽  
Ex Vivo ◽  
Current Model ◽  
Damage Threshold ◽  
Thermal Therapy ◽  
Published Data ◽  
Thermal Dose ◽  
Model Based ◽  
Dose Model

Thermal dose models are metrics that quantify thermal damage in tissues based on the temperature and the time of exposure. The validity and accuracy of one of the commonly used models (CEM₄₃) for high temperature thermal therapy applications (50-90 degree Celcius) is questionable. It was found to over-estimate the accumulation of thermal damage for high-temperature applications. A new CEM₄₃ dose model based on Arrhenius type Vogel-Tammann-Fulcher equation using published data is introduced in this work. The new dose values for the same damage threshold that was produced at different in-vivo skin experiments were in the same order of magnitude, while the current dose values were 2 orders of magnitude different. The new dose values for same damage threshold in 6 lessions in ex-vivo liver experiments were more consistent than the current dose values. Computer simulations of laser interstitial thermal therapy showed that the current model usually predicts bigger volume than the new model does. The deviation in damaged volume prediction can be significant. The contribution of this work is introducing methods that can lead to more robust thermal dosimetry which will result in improved therapy modelling, monitoring and control.

scholarly journals A new CEM₄₃ thermal dose model based on Vogel-Tammann-Fulcher behaviour in thermal damage processes

2021 ◽  
Author(s):  
Hisham Assi
Keyword(s):  
High Temperature ◽  
Thermal Damage ◽  
Ex Vivo ◽  
Current Model ◽  
Damage Threshold ◽  
Thermal Therapy ◽  
Published Data ◽  
Thermal Dose ◽  
Model Based ◽  
Dose Model

Thermal dose models are metrics that quantify thermal damage in tissues based on the temperature and the time of exposure. The validity and accuracy of one of the commonly used models (CEM₄₃) for high temperature thermal therapy applications (50-90 degree Celcius) is questionable. It was found to over-estimate the accumulation of thermal damage for high-temperature applications. A new CEM₄₃ dose model based on Arrhenius type Vogel-Tammann-Fulcher equation using published data is introduced in this work. The new dose values for the same damage threshold that was produced at different in-vivo skin experiments were in the same order of magnitude, while the current dose values were 2 orders of magnitude different. The new dose values for same damage threshold in 6 lessions in ex-vivo liver experiments were more consistent than the current dose values. Computer simulations of laser interstitial thermal therapy showed that the current model usually predicts bigger volume than the new model does. The deviation in damaged volume prediction can be significant. The contribution of this work is introducing methods that can lead to more robust thermal dosimetry which will result in improved therapy modelling, monitoring and control.

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