Technical note: The design and validation of a multi-modality lung phantom

BACKGROUND

Clinically relevant models that enable certain tasks such as calibration of medical imaging devices or techniques, device validation, training healthcare professionals, and more are vital to research throughout the medical field and are referred to as phantoms. Phantoms range in complexity from a vile of water to complex designs that emulate in vivo properties.

PURPOSE

Specific phantoms that model the lungs have focused on replication of tissue properties but lack replication of the anatomy. This limits the use across multiple imaging modalities and for device testing when anatomical considerations as well as tissue properties are needed. This work reports a lung phantom design utilizing materials that accurately mimic the ultrasound and magnetic resonance imaging (MRI) properties of in vivo lungs and includes relevant anatomical equivalence.

METHODS

The tissue mimicking materials were selected based on published studies of the materials, through qualitative comparisons of the materials with ultrasound imaging, and quantitative MRI relaxation values. A PVC ribcage was used as the structural support. The muscle/fat combined layer and the skin layer were constructed with various types of silicone with graphite powder added as a scattering agent where appropriate. Lung tissue was mimicked with silicone foam. The pleural layer was replicated by the interface between the muscle/fat layer and the lung tissue layer, requiring no additional material.

RESULTS

The design was validated by accurately mimicking the distinct tissue layers expected with in vivo lung ultrasound while maintaining tissue-mimicking relaxation values in MRI as compared to reported values. Comparisons between the muscle/fat material and in vivo muscle/fat tissue demonstrated a 1.9% difference in T1 relaxation and a 19.8% difference in T2 relaxation.

CONCLUSIONS

Qualitative US and quantitative MRI analysis verified the proposed lung phantom design for accurate modeling of the human lungs.

A High-Fidelity Agar-Based Phantom for Ultrasonography-Guided Brain Biopsy Simulation: A Novel Training Prototype with Visual Feedback

OBJECTIVE

A novel agar-based phantom was developed and assessed for ultrasonography (USG)-guided brain biopsy training. The phantom provides visual cues combined with sonologic cues, allowing multimodal training. Impact of multimodal training is evaluated through pretraining and posttraining trials.

METHODS

Twenty-five participants were divided based on experience with USG-based procedures into familiar (≥3 procedures performed in the past) (n = 14) and unfamiliar (<3 procedures performed) (n = 11). Agar phantoms with an opaque top and transparent middle layer were constructed in transparent glass bowls, each having 12 embedded targets. Participants underwent 2 supervised trials of USG-guided biopsy with aluminum foil covering the glass bowls, eliminating visual cues. Between 2 trials, participants underwent unsupervised self-training on a phantom without foil cover, providing visual cues. Performance was measured through insonation efficiency (EfI), biopsy efficiency (EfB), efficiency score (Ef), error score (Er), and performance score (PS). Scores were compared between and within the 2 groups before and after training. Impact of the self-training session on subjective comfort levels with the procedure was assessed through feedback forms.

RESULTS

Familiars had better pretraining EfB, Ef, Er, and PS (P < 0.001) compared with unfamiliars. After training, both performed similarly on all metrics. After training, familiars improved only in EfI (P = 0.001), with the unfamiliars showing significance in all metrics except EfI.

CONCLUSIONS

Simulation and phantom-based models can never supplant training through supervised skill application in vivo but our model supplements training by enabling technical skill acquisition, especially for beginners in USG-guided brain biopsy.

3D X-ray based visualization of directional deep brain stimulation lead orientation

Knowing the orientation of directional deep brain stimulation electrodes enables imaging-based adjustment of the stimulation settings. A rotational X-ray based examination was developed to determine the electrodes orientation. By identifying the patient´s 0° axis and the electrode´s rotation using the "iron sights"-sign, the exact orientation of the electrode in relation to the ACPC-line is given. The presented imaging approach offers a reliable diagnostic tool for visualization of the implanted DBS electrode orientation in clinical routine.

Customized Low-Cost Model for Hands-on Training in Intraoperative Ultrasound for Neurosurgeons: Our Experience and Review of Literature

BACKGROUND

Practical ultrasound (US) training is essential to overcome operator dependence and optimize image acquisition. For intraoperative neurosurgical application, in addition to hand-eye coordination, ultrasound training should incorporate training for visuomotor and visuospatial skills, as well as 3-dimensional depth orientation. Our agar-based, low-cost model has been developed keeping these skill sets in mind.

MATERIALS AND METHODS

We have described preparation of an agar-based, low-cost customizable model using commonly available echogenic objects as targets, which allows the clinician to perform various training tasks like depth insonation, target localization, and biopsy and resection cavity insonation. This low-cost model was implemented for internal training and validated at an international training course.

RESULTS

The cost of the model was 4 USD, and its preparation time was <1 hour. It can be used for performing multiple US training tasks and provides realistic images and good tactile feedback. However, the model is perishable and artifacts are occasionally visible. Feedback survey results showed that >80% of participants felt the model was useful for US training.

CONCLUSIONS

Our customizable low-cost US training model is an effective and efficient tool for US training with high acceptance by neurosurgeons. It faithfully mimics various intraoperative tasks and helps clinicians gain confidence to use intraoperative ultrasound as an adjunct during the procedures. This model can be used by individual surgeons/departments for ongoing training, as well as for larger training courses and workshops.

Effect of Training on Percutaneous Glycerol Rhizotomy for Trigeminal Neuralgia: A Long-Term, Retrospective Comparison of Staff Neurosurgeon and Trainee Complications and Efficacy

OBJECTIVE

The role of trainee involvement in lesioning procedures for trigeminal neuralgia (TN) has not yet been investigated in reported studies. The objective of the present study was to compare the complications and efficacy of percutaneous glycerol rhizotomy (GR) when performed by staff neurosurgeons and trainees.

METHODS

A retrospective medical record analysis of 165 patients with medically refractory TN who had undergone 293 GR procedures by either a staff attending (n = 156) or trainee (n = 137) from 2007 to 2018 was performed. The data were analyzed with respect to procedure time, fluoroscopy time and radiation exposure, complication rates and outcomes.

RESULTS

No difference was found in procedure duration between the teaching and nonteaching cases and only a nonsignificant trend was found toward a longer fluoroscopy time for the latter. The initial response rates to GR were equal for staff attending (88.7%) and trainee (87.2%) cases (P = 0.708). Similarly, no statistically significant difference (P = 0.48) was found between the median time to recurrence for the staff attending cases (1.6 ± 0.3 years) compared with that of the trainee cases (1.7 ± 0.3 years). The overall incidence of complications was low (7.5%). The occurrence of facial hypoesthesia correlated with the amount of glycerol injected (P < 0.01).

CONCLUSIONS

GR for the treatment of TN can safely be performed by senior residents and fellows under supervision.