Bien Soo Tan

Perioperative Endovascular Internal Iliac Artery Occlusion Balloon Placement in Management of Placenta Accreta

OBJECTIVE The purpose of our study was to evaluate the efficacy of the perioperative placement of occlusion balloons within the internal iliac arteries in reducing intraoperative blood loss and transfusion requirements during cesarean delivery for women with placenta accreta or its variants. MATERIALS AND METHODS Over a 30-month period, 11 patients with placenta accreta or its variants underwent cesarean delivery after bilateral internal iliac artery occlusion balloon placement (study group). The intraoperative blood loss and transfusion volumes, immediate postoperative change in hemoglobin levels, duration of surgery, and length of ICU stay and hospitalization of this study group were compared with 14 similar patients who underwent cesarean delivery without occlusion balloon placement over a 36-month period (control group). RESULTS The mean intraoperative blood loss in the study group (2,011 mL; range, 400-5,000 mL) was 39.4% less than in the control group (3,316 mL; range, 1,000-4,000 mL) (p = 0.042). The mean volume of blood transfused was 52.1% less in the study group (1,058 mL; range, 0-3,600 mL) than in the control group (2,211 mL; range, 1,190-3,980 mL) (p = 0.005). There was no significant difference in the immediate postoperative change in hemoglobin levels (p = 0.44), length of hospitalization (p = 0.203), or ICU admission (p = 0.614). The duration of the surgery was significantly less in the study group (p = 0.046). CONCLUSION Perioperative internal iliac artery occlusion balloon placement is a safe and minimally invasive technique that reduces intraoperative blood loss and transfusion requirements in patients with placenta accreta and its variants undergoing cesarean delivery.

Technical Note: Automatic real-time ultrasound tracking of respiratory signal using selective filtering and dynamic template matching

PURPOSE In respiratory motion modeling for liver interventions, the respiratory signal is usually obtained by using special tracking devices to monitor external skin. However, due to intrinsic limits and cost consideration of these tracking devices, a purely ultrasound image-based approach to tracking the signal is a more feasible option. METHODS In this study, a novel image-based method is proposed to obtain the respiratory signal directly from 2D ultrasound images by automatically identifying and tracking the liver boundary. The boundary identification is a multistage process, which is the key to utilize a Hessian matrix-based 2D filter to enhance the line-like liver boundary and weaken other liver tissues. For tracking the identified boundary, a new dynamic template matching technique is first applied to estimate 2D displacements, and a boundary-specific selection mechanism is then introduced to extract the respiratory signal from the 2D displacements. RESULTS The experiments demonstrate that their method can obtain accurate breathing signals, which are in key phases comparable to the manually annotation and highly consistent to the electromagnetic-tracked ground-truth signals (average correlation coefficients 0.9209 and statistically significant p < 0.01). Meanwhile, the experiments also prove their method can achieve high real-time performance of about 80-160 Hz. CONCLUSIONS This method provides a good alternative to traditional external-landmark-based tracking methods and may be widely applied for respiratory compensation in ultrasound-guided liver interventions.

Diagnosis and Management of Complications from Percutaneous Biliary Tract Interventions

Complications related to percutaneous biliary tract interventions (PBTIs) can range from access site discomfort to life-threatening vascular complications. These complications are relatively uncommon, and most of them are self-limiting. However, major complications for which an increased level of patient care and/or a prolonged hospital stay are required and that may lead to death-albeit rarely-can occur. Some of the most common complications related to PBTI include pain, infection, bile leakage, and catheter blockage. These conditions can be easily recognized by using the patients clinical history and laboratory examination results. However, the more uncommon complications, such as life-threatening hemobilia, acute pancreatitis, and catheter and stent fractures, may have nonspecific clinical manifestations, and the underlying pathologic condition may be found only when it is being sought specifically. It is important that diagnostic and interventional radiologists be aware of the wide spectrum of PBTI-related complications, as early recognition and treatment may prevent catastrophic situations. In addition, knowledge of the different treatment options is essential for guidance in interventional radiology procedures such as transarterial control of hemobilia, imaging-guided direct percutaneous embolization of pseudoaneurysms, and percutaneous treatment of catheter- and stent-related complications such as fractures. The authors review a wide spectrum of complications associated with PBTI and the percutaneous management of these conditions. They also highlight valuable lessons learned from morbidity and mortality rounds at a high-volume tertiary care center. ©RSNA, 2017.

A manifold learning method to detect respiratory signal from liver ultrasound images

Respiratory gating has been widely applied for respiratory correction or compensation in image acquisition and image-guided interventions. A novel image-based method is proposed to extract respiratory signal directly from 2D ultrasound liver images. The proposed method utilizes a typical manifold learning method, based on local tangent space alignment based technique, to detect principal respiratory motion from a sequence of ultrasound images. This technique assumes all the images lying on a low-dimensional manifold embedding into the high-dimensional image space, constructs an approximate tangent space of each point to represent its local geometry on the manifold, and then aligns the local tangent spaces to form the global coordinate system, where the respiratory signal is extracted. The experimental results show that the proposed method can detect relatively accurate respiratory signal with high correlation coefficient (0.9775) with respect to the ground-truth signal by tracking external markers, and achieve satisfactory computing performance (2.3s for an image sequence of 256 frames). The proposed method is also used to create breathing-corrected 3D ultrasound images to demonstrate its potential application values.

Severe acute respiratory syndrome: 11 years later--a radiology perspective.

OBJECTIVE Severe acute respiratory syndrome (SARS) was a highly virulent atypical pneumonia caused by a novel coronavirus that resulted in a pandemic in 2003. Singapore was one of the most severely affected countries, and SARS took a heavy toll on our health care system. The lessons learned during the pandemic have shaped our national contagion response plan and have proved valuable in subsequent epidemics. We describe the lessons learned for the radiology department. CONCLUSION Our experience with SARS has shaped and changed our daily practice of radiology.

Application of a standardised protocol for hepatic venous pressure gradient measurement improves quality of readings and facilitates reduction of variceal bleeding in cirrhotics.

INTRODUCTION Hepatic venous pressure gradient (HVPG) measurement is recommended for prognostic and therapeutic indications in centres with adequate resources and expertise. Our study aimed to evaluate the quality of HVPG measurements at our centre before and after introduction of a standardised protocol, and the clinical relevance of the HVPG to variceal bleeding in cirrhotics. METHODS HVPG measurements performed at Singapore General Hospital from 2005-2013 were retrospectively reviewed. Criteria for quality HVPG readings were triplicate readings, absence of negative pressure values and variability of ≤ 2 mmHg. The rate of variceal bleeding was compared in cirrhotics who achieved a HVPG response to pharmacotherapy (reduction of the HVPG to < 12 mmHg or by ≥ 20% of baseline) and those who did not. RESULTS 126 HVPG measurements were performed in 105 patients (mean age 54.7 ± 11.4 years; 55.2% men). 80% had liver cirrhosis and 20% had non-cirrhotic portal hypertension (NCPH). The mean overall HVPG was 13.5 ± 7.2 mmHg, with a significant difference between the cirrhosis and NCPH groups (p < 0.001). The proportion of quality readings significantly improved after the protocol was introduced. HVPG response was achieved in 28 (33.3%, n = 84) cirrhotics. Nine had variceal bleeding over a median follow-up of 29 months. The rate of variceal bleeding was significantly lower in HVPG responders compared to nonresponders (p = 0.025). CONCLUSION The quality of HVPG measurements in our centre improved after the introduction of a standardised protocol. A HVPG response can prognosticate the risk of variceal bleeding in cirrhotics.

Severe Bleeding after Percutaneous Transhepatic Drainage of the Biliary System

We thank Dr Nyman for his comments about our study (1). The James formula (2) is commonly used for calculating the contrast material dose for CT (3–5). It is also incorporated into many modern positron emission tomography/CT systems to calculate the standardized uptake value based on the LBW (6). We fully agree with Dr Nyman that the James formula is not necessarily appropriate in patients with a high BMI and that the Boer formula is more appropriate in such patients. In our study, the mean BMI for women and men was 22.2 kg/m2 (range, 13.2–36.7 kg/m2) and 22.4 kg/m2 (range, 12.1–42.0 kg/m2), respectively. In this population, there is a very strong linear correlation between the estimated LBW calculated with the James formula and the estimated LBW obtained with the Boer formula. The correlation coefficient was 0.981 (95% confidence interval: 0.979, 0.983), and the mean difference in the estimated LBW calculated with the two methods was 0.127 kg (range, −6.88 to 4.65 kg). Therefore, almost the same results are obtained with the Boer and the James formula. The Janmahasatian formula (7) is another formula for estimating the LBW; it can be applied in patients with a high BMI. As it involves an increasing function of weight and plateaus at large weight values, it can be applied in a wide range of body weights. Studies are needed to assess whether the Boer or the Janmahasatian formula is better for estimating the LBW for the determination of the appropriate contrast material dose.

Hemodialysis Arteriovenous Fistula and Graft Stenoses: Randomized Trial Comparing Drug-eluting Balloon Angioplasty with Conventional Angioplasty

Purpose To compare lesion primary patency and restenosis rates between drug-eluting balloon (DEB) percutaneous transluminal angioplasty (PTA) and conventional balloon PTA (cPTA) in the treatment of arteriovenous fistula (AVF) and arteriovenous graft (AVG) stenosis. Materials and Methods In this prospective study, 119 participants (mean age, 59.2 years; 79 men, 40 women) with failing AVFs (n = 98) or AVGs (n = 21) were randomly assigned to undergo either DEB PTA (n = 59) or cPTA (n = 60) from January 2012 to May 2013. Primary end points were lesion primary patency and restenosis rates at 6 months; secondary outcomes were anatomic and clinical success after PTA, circuit primary patency at 6 months and 1 year, and lesion primary patency at 1 year. Statistical analysis was performed by using the Kaplan-Meier product limit estimator, and hazard ratio was calculated by using Cox proportional hazards regression. Complication rates were assessed in both groups. Results Estimated lesion primary patency in the DEB PTA and cPTA arms was 0.81 and 0.61, respectively, at 6 months (P = .03) and 0.51 and 0.34, respectively, at 1 year (P = .04). Estimated circuit primary patency in the DEB PTA and cPTA arms was 0.76 and 0.56, respectively, at 6 months (P = .048) and 0.45 and 0.32, respectively, at 1 year (P = .16). Restenosis rate was 34.0% (16 of 47) for DEB PTA and 62.9% (22 of 35) for cPTA at 6 months (P = .01). No major complications were noted. Conclusion Drug-eluting balloon angioplasty was effective in prolonging lesion primary patency of dialysis access stenoses at 6 months and 1 year.

Subject-specific and respiration-corrected 4D liver model from real-time ultrasound image sequences

Abstract Respiratory liver motion is one of the major issues affecting the liver interventions, such as biopsy and ablation, in the clinical practice. Traditional 4D liver model methods using magnetic resonance imaging (MRI) or computed tomography (CT) data sets for motion compensation to solve this problem have proved time-consuming and costly. In addition, the widely used freehand 3D ultrasound techniques, which lack respiratory corrections, cannot effectively track breathing-induced liver motion. On the other hand, clinical solutions are straightforward but present restrictions for patients. Motivated by both the technical and clinical needs, we propose a novel method for creating a sequence of subject-specific and respiration-corrected 3D ultrasound (US) images, from multiple robotic-assisted-swept 2D US image sequences. Moreover, we also observed the motion difference between subjects on the generated 4D model. The results of quantitative evaluation on the accuracy of the models show that the overlap ratio of the liver boundary between the generated model and ground truth at end of exhale and end of inhale phases were 0.90 and 0.89, respectively. The overall distance error of pinpointed landmarks was 2.44 mm, which is within the acceptance range of clinical applications. Therefore, we conclude that the reconstructed 3D image sequence can capture the moving liver during a half respiratory cycle, and the proposed method is feasible to visualise the 3D liver motion. The clinicians who worked with us in this study also suggest that this preoperative subject-specific motion information could help them to diagnose the existence, or determine the possible position, of a tumour.

CREATION OF CLINICALLY-DIFFERENTIAL TUMOR MIMIC MODEL USING VASELINE-BASED MATERIALS WITH BARIUM SULFATE FOR THE VALIDATION OF REAL-TIME ULTRASOUND IMAGE-GUIDED LIVER BIOPSY SYSTEM

Testing objects are important for the validation of developing biopsy systems. Unfortunately, they are very hard to obtain. Motivated by this issue, the purpose of this study is to develop a technique for the easy creation of a model to simulate tumors of different sizes inside porcine livers, which could be used for ultrasound image-guided liver biopsy amongst other applications, and evaluate its performance by comparing to the more widely-used approaches in-vivo and ex-vivo. In this study, a Vaseline-based tumor model, and a more widely-used agar-based tumor model to provide comparison with the proposed method were created and injected into porcine livers as biopsy targets. The clinician located simulated tumors using real-time 2D imaging under the guidance of a robotic arm to delivery the biopsy in ex-vivo and in-vivo experiments. The results show that the optimum tumor model was created from a mixture of Vaseline, glycerol, and barium sulfate which can be easily produced and injected. All Vaseline-based simulated tumors were of solid, palpable mass on gross examination, and ultrasound imaging revealed clearly visible lesions. The clinician successfully performed ultrasound image guided liver biopsy in all the trials (10/10) in the ex-vivo experiment, and 2 out of 3 trials (2/3) in the in-vivo experiment on this optimum tumor model. We described a novel technique of creating solid liver tumor models that can be used for ultrasound image-guided liver biopsy.