Letter: The Role of Skull Thickness Beyond the Skull Density Ratio on MRgFUS Thalamotomy Feasibility: Which Patients Should We Exclude?

Pineda‐Pardo, José A.; Máñez-Miró, Jorge U; López-Aguirre, Miguel; Rodríguez‐Rojas, Rafael; Caballero‐Insaurriaga, Jaime; M, Del Álamo; Martínez‐Fernández, Raúl; Obeso, José A.

doi:10.1093/neuros/nyz566

Cited by 14 publications

(25 citation statements)

References 12 publications

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“…Patients with a lower SDR and a higher ST required a greater amount of delivered energy during sonication to reach the desired temperature. This relationship has been previously defined in the literature 12–18 . This same association was observed regarding aborted sonication because of unbearable headaches.…”

Section: Discussionsupporting

confidence: 78%

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Factors Associated with Headache and Nausea During Magnetic Resonance–Guided Focused Ultrasound for Tremor

Cacho‐Asenjo

Honorato‐Cia

Núñez‐Córdoba

et al. 2021

Movement Disord Clin Pract

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BackgroundBackground: During magnetic resonance-guided focused ultrasound for essential or parkinsonian tremor, adverse events (headache, nausea/vomiting, or anxiety) may alter the outcome of the procedure despite being mostly transient and mild. Objectives Objectives: Our aim was to analyze the relationship between demographic, procedural, and anesthetic characteristics with magnetic resonance/ultrasound-related events. Methods Methods: This was a retrospective study at the Clinica Universidad de Navarra of patients undergoing thalamotomy with magnetic resonance-guided focused ultrasound between September 2018 and October 2019. The anesthesia protocol included headache and nausea/vomiting prophylaxis and rescue therapy. Dexmedetomidine was used for anxiolysis in some patients after thorough multidisciplinary assessment. Results Results: A total of 123 patients were included. Headache was directly related to skull density ratio (P < 0.001) and skull thickness (P = 0.02). Patients with a skull density ratio less than 0.48 had 3 times the odds of experiencing moderate or severe headache (odds ratio [OR], 3.08; 95% confidence interval [CI], 1.21-7.82) and had a higher odds of aborting sonication due to pain. Sex was associated with increased nausea (P = 0.007). Women had 4 times the odds of nausea than men (OR, 4.4; 95% CI, 1.61-12.11). Dexmedetomidine did not reduce headache or nausea incidence. Patients who received dexmedetomidine had a higher number (P = 0.01) and total minutes of sonication (P = 0.01). Conclusions Conclusions: Patients with lower skull density ratios and higher skull thicknesses could benefit from an aggressive analgesic prophylaxis. Women are more likely to experience nausea. Dexmedetomidine did not reduce headache and nausea, but increased the number and duration of sonications. Its exact effect on tremor is still unclear.

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Section: Discussionsupporting

confidence: 78%

“…This relationship has been previously defined in the literature. [12][13][14][15][16][17][18] This same association was observed regarding aborted sonication because of unbearable headaches. Patients with a lower SDR and a higher ST could benefit from a more aggressive analgesic prophylaxis, including opioids.…”

Section: Discussionsupporting

confidence: 66%

Factors Associated with Headache and Nausea During Magnetic Resonance–Guided Focused Ultrasound for Tremor

Cacho‐Asenjo

Honorato‐Cia

Núñez‐Córdoba

et al. 2021

Movement Disord Clin Pract

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“…The ability to reach lesional temperatures can be conceptualized in terms of the efficiency of acoustic energy transmission to the target, or heating efficiency (HE). As the skull represents a major barrier for ultrasound waves propagating towards the target, there has been much interest in the relationship between HE and patient‐specific skull morphology 6,8,13–18 . In particular, skull density ratio (SDR) has been proposed as a useful metric of the skull's transmission efficiency, and is defined as the ratio between the density of cancellous bone and the density of cortical bone (see Section 2.2 for details) 13 .…”

Section: Introductionmentioning

confidence: 99%

“…In particular, skull density ratio (SDR) has been proposed as a useful metric of the skull's transmission efficiency, and is defined as the ratio between the density of cancellous bone and the density of cortical bone (see Section 2.2 for details) 13 . SDR ranges between 0 and 1 (indicating high or low heterogeneity between the densities, respectively), and positively correlates with maximum temperatures achieved at the target 6,8,13–19 . For this reason, SDR of

\geq

0.45 was specified as an inclusion criterion in the two pivotal trials, 1,2 and current FDA labelling only includes patients with SDR

\geq

0.45

\pm

0.05 20…”

Section: Introductionmentioning

confidence: 99%

“…Since the initial clinical trials, patients with SDR < 0.45 have been treated based on medical need, 6,17 including at our institution. Recent studies have demonstrated that equivalent clinical outcomes can be achieved in patients with low SDR 6,8,14,17,25 . However, the implications of SDR on the optimal strategy to achieve lesional temperatures are not well understood.…”

Section: Introductionmentioning

confidence: 99%

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Patient‐specific effects on sonication heating efficiency during magnetic resonance‐guided focused ultrasound thalamotomy

et al. 2021

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During magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy for refractory tremor,high temperatures must be achieved and sustained for tissue necrosis. We assessed the impact of both patient-specific as well as procedure-related factors on the efficiency of acoustic energy transfer, or heating efficiency (HE). Methods: Retrospective analysis of 92 consecutive patients (857 sonications) with essential tremor or tremor-dominant Parkinson's disease treated at a single institution. Temperature elevations at the target were measured for each sonication with MR thermometry. HE of each sonication was defined as the ratio of peak temperature elevation and the delivered energy. HE was analyzed with respect to patient skull features (area, thickness, skull density ratio [SDR]), computed from CT scans, as well as demographic and clinical variables (age, sex, diagnosis, and duration of symptoms). Results: Across the full range of sonication energies that can be delivered with current devices (up to 36 kJ), average sonication HE was diminished in patients with lower SDR. In individual subjects, there was a progressive loss in HE as sonication energy was titrated up throughout the course of treatment, with a more rapid decline in patients with higher SDR. This energy-dependent loss in HE was not related to procedural factors, namely, the number of previous sonications, or the cumulative energy deposited during previous sonications. In contrast to SDR, neither skull area nor thickness was an independent predictor of average HE or the rate of its decline with increasing energies. In 11% of patients, all of whom with SDR < 0.45, sonication HE fell below the threshold to reach 54 • C even with delivery of maximum energy. In contrast, temperatures ≥50 • C could be obtained in all but one patient. Conclusions: SDR is predictive of sonication HE, and determines patientspecific limits on the magnitude of temperature elevation that can be achieved with current devices. These data inform strategies for predictable lesioning in MRgFUS thalamotomy.

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Skull Density Ratio as Arm‐Allocation Parameter for a Controlled Focused Ultrasound Trial in Parkinson's Disease

Pineda‐Pardo,

Martínez‐Fernández,

Natera‐Villalba

et al. 2024

Movement Disord Clin Pract

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BackgroundMR‐guided focused ultrasound (FUS) thermoablation is an established therapy for movement disorders. FUS candidates must meet a predefined threshold of skull density ratio (SDR), a parameter that accounts for the efficiency in reaching ablative temperatures. Randomized sham‐controlled trials to provide definitive therapeutic evidence employ pure randomization of subjects into active treatment or control arms. The latter design has several general limitations.ObjectiveTo demonstrate that SDR values are not associated with clinically and demographically relevant variables in patients with Parkinson's disease (PD). This in turn would allow using SDR as an arm‐allocation parameter, separating patients who will receive active FUS treatment and best medical management treatment (BMT).MethodsWe studied a cohort of 215 PD patients who were candidates for FUS subthalamotomy to determine if the SDR was correlated with demographic or clinical variables that could introduce bias for group allocation in a controlled trial.ResultsSDR was unassociated with age, gender, and clinical motor features nor with levodopa daily dose in our cohort of PD patients. A negative association with age was found for the female subgroup.ConclusionsOur results show that in a PD population considered for FUS subthalamotomy treatment, the SDR may be a valid group‐allocation parameter. This could be considered as the basis for a controlled study comparing FUS subthalamotomy vs BMT.

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Letter: The Role of Skull Thickness Beyond the Skull Density Ratio on MRgFUS Thalamotomy Feasibility: Which Patients Should We Exclude?

Cited by 14 publications

References 12 publications

Factors Associated with Headache and Nausea During Magnetic Resonance–Guided Focused Ultrasound for Tremor

Factors Associated with Headache and Nausea During Magnetic Resonance–Guided Focused Ultrasound for Tremor

Patient‐specific effects on sonication heating efficiency during magnetic resonance‐guided focused ultrasound thalamotomy

Skull Density Ratio as Arm‐Allocation Parameter for a Controlled Focused Ultrasound Trial in Parkinson's Disease

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