A Gradient Needle Array Transducer For Real-time Puncture Guidance

Epidural anesthesia is widely used as a clinical anesthetic technique in operations like painless delivery,post-operative analgesia,cardiac muscle protection and combined spinal epidural anesthesia as well as operations combined with trachea anesthesia.By injecting anesthetic into the space between ligamentum flavum and endorhachis,the diffused medicine narcotizes the nerve root,which passes through the foramen of the cavity.It blocks the transmission of spinal nerves and realizes local anesthesia.Currently on clinic,doctors perform the needle insertion based on their clinical experiences and subjective hand feeling.This operation requires high skill of proficiency.At present,technologies such as pressure detection,electric stimulation and optical detection function as methods to judge the effects of puncture,but none of them can provide clear images easily.With advantages of low cost,great convenience,high penetration ability,large imaging depth and no ionizing radiation,etc.,ultrasound equipment can use the pulseecho to form a distinct image to distinguish tissues and provide real-time guidance.The transducer for extraneous imaging guidance will send or receive ultrasound wave that easily encountering the blockade of bones and gets low resolution imaging while the single element needle transducer for intracorporal imaging guidance only gets one echo signal rather than images of the surrounding tissues in the fixed position.In this study,a novel gradient needle array transducer for real-time puncture guidance is proposed.Electric focusing of the transducer is realized by adjusting the phase of elements.The transducer employs the gradient structure to expand the depth and field of imaging in a small size,and provides real-time puncture guidance for the process of needle insertion.From the Field Ⅱ simulation results of the phantom imaging,it is showed that the gradient needle array transducer will provide images with lower artifacts generating from grating lobes when the pitch between elements is larger than half wavelength compared with the results of the 2D-array transducer.To optimize the parameters of fabrication,the size and material of the gradient needle array transducer are acquired from the simulation of PiezoCAD.The electric input impedance,phase angle,pulseecho as well as frequency spectrum are also simulated.The gradient needle array transducer is fabricated by steps of grinding PZT-5H,vacuum metallizing,making matching layer and backing layer,slicing elements and making one row of elements.Then these elements are picked to be adhered to the flexible plates and laminated to be an intact gradient needle array transducer.The fabricated transducer has equal element width and element height of 110μm,as well as the element thickness of 109μm.The number of total elements is 64.56 of them are used as active imaging elements while 8 elements working as grounded elements.The element has a center frequency of 17.3MHz,a bandwidth of 42.6% at-6dB,and the crosstalk between elements is less than-23.81 dB.Finally,real-time 2D imaging is accomplished based on the Verasonics Vantage 256 systems in phantom imaging and in vitro animal experiments.With techniques such as electronic delay,beamforming and dynamic focusing,2D imaging and 3D imaging of wire phantoms were acquired.The localization of the surrounding bones during the procedure of puncture guidance can be distinguished in real-time.This research work proposes a gradient needle array needle array transducer for real-time puncture guidance.Compared with current 2D-array transducers whose pitch between elements are within half wavelength,this transducer lessens grating lobes of the imaging,enlarges the size of elements,and improves the efficiency of transmission and reception as well as frequency of the transducer.Because the shape of the transducer is identical with the shape of the tuohy,the blockade of the tuohy decreases and the imaging area enlarges.This article discusses the feasibility of the gradient needle array transducer for real-time puncture guidance from the perspective of simulation,fabrication and imaging.It will provide a new imaging reference for safe,adequate,real-time puncture guidance with 3D imaging and decrease the risk of failure in epidural anesthesia in the future clinical operations.