| Background and objectives:Renal stone is a frequently-occurring and common disease, accounting for40%of the urinary surgery. Percutaneous nephrolithotomy (PCNL) has been the gold standard approach for managing large, multiple, or inferior calyx renal stones for its small trauma and high calculi clearance rate.Kidney is one of the internal organs rich in blood supply, and renal blood flow account for20%-25%of cardiac output in a resting state. The distribution of intrarenal arteries is segmental and lacks of traffic to each other. Ischemic necrosis will occur in the region where renal artery is injured and loss arterial blood supply. The traces of renal arteries are not along or follow the direction of the calyx. It does not mean that the area in the location1cm behind the kidney flange called Brodel tangent really no vessel. It is only fewer blood vessels relatively. Graves etc. divided renal pelvis and calyces arrangement into type A, B, C, and D by casting kidney collecting system. The most common type D, small ball of the renal pelvis, slender stem shape of calyces, with alternating calyces overlapping fusion, only using CT scanning and three-dimensional (3D) reconstruction or oblique and lateral IVP radiography can display its three-dimensional structure. Congenital anomalies of renal abnormal rotation such as horseshoe kidney always appear abnormal renal artery and vein in the renal hilum. The distribution of renal vascular and collection system configurations is more difficult to predict.The internal anatomy of the kidney itself is diverse and different and usually changes much caused by urinary tract obstruction of renal stones. So the percutaneous nephrolithotomy, the minimally invasive surgery treatment for renal stones, there is still a lot of unpredictability. The most common complications of PCNL are bleeding and infection. The intraoperative and postoperative massive bleeding is about13.7%. And the pleural injury incidence ranges from4.5%to16%. The incidence of adjacent viscera damage is about0%to0.4%. Multichannel or multistage is needed to clear stone for complex renal stones, but it would increase the risk of surgical bleeding. The reason of massive hemorrhage mainly is arteriovenous fistula or pseudoaneurysm caused by surgery. Most often it require renal artery embolization to cure. How to improve the one-stage stone-free rate and reduce the complications of kidney stones treatment is the key of PCNL research. The stone-free rate has close relation with the size, location, and distribution of renal stones and the collection system. It will help to evaluate patients surgical risk and establish reasonable puncture path if clearly know the distribution of intrarenal artery and the relationship between the renal pelvis and calyces.The major and most difficult step is the ability to establish an appropriate access route. The risk of surgical and stone-free rate is largely related to renal puncture path choice and set up. PCNL is frequently performed with B-ultrasound and fluoroscopy guided access. However, these only provide a single-plane two-dimensional image, having a low resolution and incompletely displaying important anatomic structures. So it is hard to avoid damaging the blood vessels and the surrounding organs. The color Doppler-ultrasound, advantage of displaying arteries and veins blood flow, helps to puncture avoiding big blood vessel damage and then reduces the operation risk of bleeding to some extent. But it is hard to establish a reasonable and effective channel because the renal internal structure display is not clear and only provide2D images.The related research how to quickly and reasonably establish puncture in domestic and international has been carried out. The most concern is the application of3D visualization technology. Oliveira Santos etc. used the computer combined with3D model of renal collecting system auxiliary puncture into the collection system. They set up a landmark on the human body model and fused the intraoperative images and3D model to targeted guidance. A. d. Zarrabi etc. designed the mechanical percutaneous renal puncture positioning equipment making up for the inadequacy of2D image displayed by C arm. It promoted the rapid puncture and reduced the dose of radiation for performer. Jens j. Rassweilera etc. acquired the intraoperative images through the ipad rear camera to fuse with the preoperative3D model of kidney stones. The feasibility and effectiveness were proved after preliminary guidance for two patients with PCNL puncture. However, most of the3D model of kidney reconstruction was only based on the single phase stage CT image date such as arterial or renal pelvis phase image. It failed to meet the real meaning of kidney3D visualization, because they only devised for entering the collection system, not considering how to get the best puncture path.So we further promote virtual visualization technology combined the3D engineering technology with medicine. Taking modern medical imaging, computer image processing, anatomy and urology to join together, we here construct a three-dimensional (3D) model of renal stones to facilitate comprehensive planning for PCNL base on64row CT images. We suggest the novel approach of PCNL virtual surgery simulation on the3D model of kidney stones using Free Form Modeling System to increase the one-stage stone-free rate and reduce complications.Method1Construction of a three-dimensional model of renal stones based on CT imageFrom January to June2012, thirty patients with renal stones who required PCNL were treated at our Department of Urology, Zhujiang Hospital of Southern Medical University,16men and14women, average age was49.6years old (35to63),left kidney stones in16cases, right in14cases.After4hours on an empty stomach, the patient lay in a prone position with the renal area of the abdomen on our PCNL cushion. Four-channel multi-detector row computed tomography (CT) images including the unenhanced phase, arterial phase, venous phase, and excretory phase were obtained using a64multi-detector row CT scanner (Philips, Brilliance64, Netherlands). The start time of the arterial phase scanning was determined by using automatic bolus tracking. Scanning was initiated after triggering at a threshold of200HU in the region of interest, which was placed in the abdominal aorta at the level of the renal arteries. The venous and excretory phase scanning began65seconds and600-900seconds respectively after intravenous injection of contrast material. Image segmentation and3D reconstruction were performed using Mimics10.0(Materialise, Leuven, Belgium). The threshold value method, region growing, boolean function and the manual division method were combined and jointly interpreted for image segmentation.The CT images were segmented focusing on all aspects of the relevant structures, including the renal parenchyma, intrarenal arteries, intrarenal veins, renal stones, the collecting system, spine, ribs, lungs, liver, spleen, and the skin of the back base on the four-channel multi-detector row computed tomography (CT) images. By set up multiple landmarks on the3D kidneys reconstructed from each phase, automatic registration was performed in mimics10.0. All the3D images were fused finally after the manual adjusting by three-dimensional displacement and rotation on the X, Y, and Zaxis.The quality of3d model of renal stone was evaluated and recorded by two experienced urologists. The effective and qualified3D model of the renal stones was be defined as:the relationship between kidney, renal blood vessels, and the collection system required to be represented simultaneously and clearly;3D kidney and adjacent organs showed clear and smooth; at least third to fourth renal arteries branches and first to second veins branches can distinguish, respectively; the collecting system was smooth and complete. Measure the effectiveness of3D reconstruction of kidney stones base on CT images through statistical analysis.2Percutaneous nephrolithotomy virtual simulation study based on the3D model of renal stonesThe3D simulation of PCNL surgical instruments scalpel, puncture needle, guide wire, fascial dilator, ballistic lithotripter were performed using3D Studio Max2012soft. The relevant data was measure on the3D model of renal stone by an experienced urinary surgeon including the volume of stone and kidney etc. The detail patients’ physiological anatomy structures were presented transparent visually through operating the model to be amplifying, revolving and transparent. The puncture location was established on the lumbar of the3D model using the3D puncture needle. The comprehensive planning for percutaneous renal puncture path was performed on the3D model of renal stones. The puncture point, route and the depth of puncture were measured. The3D model of renal stone with a plan puncture needle was imported to stage of Free Form Modeling Plus. PCNL surgery simulation operation were performed on the3D model of renal stone using the3D simulation surgical instruments which operated by the three-dimension mouse. The operation simulation processes of ureteral catheterization, expansion of puncture, pneumatic lithotripsy and nephrostomy tube placement were all performed.Result1Construction of a three-dimensional (3D) model of renal stones based on CT imageA total of30patients involved in this study,16men and14women, average age was49.6years old, left kidney stones in16cases, right in14cases, including1patient (3.3%) with a horseshoe kidney,6patients (20.0%) with partial/complete staghorn, and10patients (33.3%) with multiple renal stones. The other13case (43.3%) was renal pelvis or calyceal stones. A total of30sets of64-slice spiral CT images in prone position including the unenhanced, arterial, venous and excretory phase were acquired, layer thickness1mm. The CT images were high contrast and spatial resolution, good at image uniformity, and less noise artifacts.30patients’ three-dimensional models of renal stones were constructed successfully. The outline of the3D model was clear and smooth. The reconstructed renal model accurately represented the actual size of the kidney and its anatomic landmarks. The third to fourth renal arteries branches and first to second veins branches represented clearly. The vascular edges were smooth, no respiratory motion artifact. The collection system structure was clear, continuous and natural.The Stone shape and number and the expansion degree of renal collecting system demonstrated visually in the3D model of renal stone. And by adjusting the transparency of the kidney, the kidney, renal stones, intrarenal arteries, intrarenal veins, and renal collecting system were clearly visualized. The model can allowed zooming and rotation for observation in full views. And the model presented with realistic profile of the kidney that allowed vivid3D observation. The effective and qualified3D model of the renal stones was28cases.2cases were not qualified due to insufficient contrast filling renal vascular, the branch of renal vascular showed less and part of renal calyx in collecting system didn’t displayed. The effectiveness of the3d renal stone model reconstruction based on CT image was93.3%.2Percutaneous nephrolithotomy virtual simulation study based on the3D model of renal stonesA set of3D simulation of PCNL surgical instruments including calpel, puncture needle, guide wire, fascial dilator, ballistic lithotripter were constructed. The Surgical instrument model was realistic with three-dimensional operability. In28cases of3D model of renal stones, the mean stone volume was7.8±2.4cm3, the mean stone surface area was21.1±12.0cm2, The mean kidney volume was157.1±13.2cm3. The mean puncture depth was8.7±1.5cm. The Percutaneous nephrolithotomy virtual simulation was all performed successfully in all28patients’ models. An11th intercostal puncture access route was devised in7cases (25.0%). Two percutaneous renal access routes were devised in3cases (10.7%) of multiple stones. According to the planned surgical puncture, the individualized PCNL virtual surgery simulations were all performed successfully on the model operated by Free Form Modeling System. The simulation operation was feasible and active, which can repeatedly operate much.Conclusion1The construction of3D model of renal stone base on64multi-detector row CT is feasible and effective. It reflects the patient’s individualized and physiological kidney anatomy structure and the surrounding adjacent organs.2The3D model of renal stones can provide comprehensive surgical planning and virtual simulation of percutaneous nephrolithotomy. It establishes the foundation for surgical percutaneous renal puncture navigation. |
PDF Full Text Request