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Background and ObjectivesUltrasound-guided regional anesthesia facilitates an approach to sensitive targets such as nerve clusters without contact or inadvertent puncture. We compared accuracy of needle placement with a novel passive magnetic ultrasound needle guidance technology (NGT) versus conventional ultrasound (CU) with echogenic needles.MethodsSixteen anesthesiologists and 19 residents performed a series of 16 needle insertion tasks each, 8 using NGT (n = 280) and 8 using CU (n = 280), in high-fidelity porcine phantoms. Tasks were stratified based on aiming to contact (target-contact) or place in close proximity with (target-proximity) targets, needle gauge (no. 18/no. 22), and in-plane (IP) or out-of-plane (OOP) approach. Distance to the target, task completion by aim, number of passes, and number of tasks completed on the first pass were reported.ResultsNeedle guidance technology significantly improved distance, task completion, number of passes, and completion on the first pass compared with CU for both IP and OOP approaches (P ≤ 0.001). Average NGT distance to target was lower by 57.1% overall (n = 560, 1.5 ± 2.4 vs 3.5 ± 3.7 mm), 38.5% IP (n = 140, 1.6 ± 2.6 vs 2.6 ± 2.8 mm), and 68.2% OOP (n = 140, 1.4 ± 2.2 vs 4.4 ± 4.3 mm) (all P ≤ 0.01). Subgroup analyses revealed accuracy gains were largest among target-proximity tasks performed by residents and for OOP approaches. Needle guidance technology improved first-pass completion from 214 (76.4%) per 280 to 249 (88.9%) per 280, a significant improvement of 16.4% (P = 0.001).ConclusionsPassive magnetic NGT can improve accuracy of needle procedures, particularly among OOP procedures requiring close approach to sensitive targets, such as nerve blocks in anesthesiology practice.

The portal vein is formed by the junction of the splenic and superior mesenteric vein. The portal/ splenic confluence is found posterior to the neck of the pancreas. The inferior mesenteric vein drains into the splenic vein to the left of the portal/splenic confluence. The left gastric or coronary vein usually joins the splenic vein superiorly near its junction with the superior mesenteric vein. It courses in a craniocaudad plane. From the confluence, the portal vein courses lateral and cephalad in an oblique plane toward the porta hepatis, where it enters the liver. Within the liver, the portal vein is found posterior to the hepatic artery and common bile duct. These three structures course together throughout the liver and are known as the portal triad.The portal vein divides at the porta hepatis into right and left branches. The right portal vein divides into anterior and posterior branches, and the left portal vein divides into medial and lateral branches. The left portal vein is in contact with the ligamentum teres.

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The testis is an ovoid-shaped gland measuring approximately 4 × 3 × 3 cm (Fig. 1). It is divided into more than 250 conical lobules containing the seminiferous tubules. These tubules converge at the apex of each lobule. The rete testis is formed by the anastomosis of these tubules in the mediastinum. It is connected to the head of the epididymis through the efferent ducts. The epididymis is a 6-to 7-cm-long structure located posterolateral to the testis. It is divided into a head (globus major), body (corpus epididymis), and tail (globus minor). The head is adjacent to the upper pole of the testis (Fig. 2). It contains 10 to 15 efferent ducts from the rete testis that converge to form a single duct known as the ductus epididymis. The body of the epididymis is much smaller than the head. It courses along the posterolateral aspect of the testis from the upper to the lower pole. It may be seen as a small hypoechoic structure containing numerous echogenic linear structures (Fig. 3). These echoes represent the coiled epididymal tube. The tail of the epididymis is slightly larger and is located posterior to the lower pole of the testis.