Dual-mode intracranial catheter integrating 3D ultrasound imaging and hyperthermia for neuro-oncology: feasibility study

Abstract

In this study, we investigated the feasibility of an intracranial catheter transducer with dual-mode capability of real-time 3D (RT3D) imaging and ultrasound hyperthermia, for application in the visualization and treatment of tumors in the brain. Feasibility is demonstrated in two ways: first by using a 50-element linear array transducer (17 mm x 3.1 mm aperture) operating at 4.4 MHz with our Volumetrics diagnostic scanner and custom, electrical impedance-matching circuits to achieve a temperature rise over 4 degrees C in excised pork muscle, and second, by designing and constructing a 12 Fr, integrated matrix and linear-array catheter transducer prototype for combined RT3D imaging and heating capability. This dual-mode catheter incorporated 153 matrix array elements and 11 linear array elements diced on a 0.2 mm pitch, with a total aperture size of 8.4 mm x 2.3 mm. This 3.64 MHz array achieved a 3.5 degrees C in vitro temperature rise at a 2 cm focal distance in tissue-mimicking material. The dual-mode catheter prototype was compared with a Siemens 10 Fr AcuNav catheter as a gold standard in experiments assessing image quality and therapeutic potential and both probes were used in an in vivo canine brain model to image anatomical structures and color Doppler blood flow and to attempt in vivo heating.

Fig. 1

Intended catheter pathway affording minimally-invasive access to the brain volume via dural venous sinuses.

Fig. 2

Integrated 2D matrix & linear array design for RT3D imaging & hyperthermia. The centered 2D array scans a pyramidal volume in real-time, and the adjacent linear arrays produce a hyperthermia beam (shown in red within the volume), steerable in azimuth (different possible foci indicated by red ‘x’s).

Fig. 3

Field II simulation apertures and beam plots. (a,b,c) Active apertures for each case: the entire integrated array with 2 cm focus, the integrated catheter's linear arrays with unfocused transmit, and the AcuNav with 2 cm focus, respectively. (d,e,f) Relative pressure amplitude in the zero-elevation plane for each case, respectively. (g,h,i) Relative pressure amplitude at a depth of 2 cm for each case, respectively.

Fig. 4

(a) Bare flex circuit above a ruler with mm markings. (b) Diced matrix and linear arrays with MicroFlat cables soldered to linear array contacts. (c) Completed dual-mode catheter transducer.

Fig. 5

(a) Center of linear array transducer used in in vitro hyperthermia experiment with Volumetrics RT3D scanner and matching circuits. (b) Thermocouple data showing a 5.0°C temperature rise in degassed, excised pork muscle.

Fig. 6

(a) AcuNav image of 4-cm deep, 1.5-cm diameter cyst phantom. (b) Dual-mode catheter single-B scan of cyst phantom. (c,d,e) Dual-mode catheter 3D scan of cyst phantom: coronal, axial, and sagittal image planes.

Fig. 7

Thermocouple data showing 3.5°C temperature rise in tissue-mimicking material using the dual-mode catheter focused at 2 cm.

Fig. 8

In vivo canine model: the dual-mode catheter (C) placed in the superior sagittal sinus through a burr hole created in the skull, and a thermocouple (T) inserted into the cerebrum through the dura mater exposed by a second burr hole, for hyperthermia trials.

Fig. 9

Intracranial AcuNav images. (a) Echo image showing various gyri and sulci of the cerebrum. (b) Color Doppler image showing the internal carotid artery.

Fig. 10

(a,b,c) Intracranial RT3D echo images in coronal, axial, and sagittal planes, respectively, compared to corresponding anatomical images (Reproduced with permission from Fletcher et al., University of Minnesota College of Veterinary Medicine). The lateral ventricles (LV) are clearly seen in (a) and (b). The tentorium (T) and cerebellum (C), as well as a posterior horn of the lateral ventricle, are visible in (c).

Fig. 11

(a,b,c) Intracranial RT3D color Doppler images in coronal, axial, and sagittal planes, respectively (note: the color Doppler look-up table was modified, eliminating directional flow information). (d) Latex-injected sheep brain vasculature for anatomical reference (Reproduced with permission from R.R. Miselis, University of Pennsylvania School of Veterinary Medicine). The internal carotid arteries (ICA), left middle cerebral artery (MCA), and anterior communicating artery (ACoA) are visible in (a). The Circle of Willis is shown in (b), with the anterior cerebral arteries (ACeA), posterior cerebral arteries (PCeA) and posterior communicating arteries (PCoA) also indicated.

Fig. 12

(a) AcuNav image of thermocouple (arrow) placed at 1 cm depth in cerebrum. (b,c,d) RT3D coronal, axial, and sagittal images, respectively, of inserted thermocouple (arrows), acquired with dual-mode catheter. (e) Temperature rise achieved using the AcuNav (transducer self-heating and conduction). (f) Temperature rise achieved by driving the dual-mode catheter's linear array elements as a single channel (unfocused) with an RF power amplifier.