The effect of tin prefiltration on extremity cone-beam CT imaging with a twin robotic X-ray system.

INTRODUCTION: While tin prefiltration is established in various CT applications, its value in extremity cone-beam CT relative to optimized spectra has not been thoroughly assessed thus far. This study aims to investigate the effect of tin filters in extremity cone-beam CT with a twin-robotic X-ray system. METHODS: Wrist, elbow and ankle joints of two cadaveric specimens were examined in a laboratory setup with different combinations of prefiltration (copper, tin), tube voltage and current-time product. Image quality was assessed subjectively by five radiologists with Fleiss' kappa being computed to measure interrater agreement. To provide a semiquantitative criterion for image quality, contrast-to-noise ratios (CNR) were compared for standardized regions of interest. Volume CT dose indices were calculated for a 16 cm polymethylmethacrylate phantom. RESULTS: Radiation dose ranged from 17.4 mGy in the clinical standard protocol without tin filter to as low as 0.7 mGy with tin prefiltration. Image quality ratings and CNR for tin-filtered scans with 100 kV were lower than for 80 kV studies with copper prefiltration despite higher dose (11.2 and 5.6 vs. 4.5 mGy; p < 0.001). No difference was ascertained between 100 kV scans with tin filtration and 60 kV copper-filtered scans with 75% dose reduction (subjective: p = 0.101; CNR: p = 0.706). Fleiss' kappa of 0.597 (95% confidence interval 0.567-0.626; p < 0.001) indicated moderate interrater agreement. CONCLUSION: Considerable dose reduction is feasible with tin prefiltration, however, the twin-robotic X-ray system's low-dose potential for extremity 3D imaging is maximized with a dedicated low-kilovolt scan protocol in situations without extensive beam-hardening artifacts. IMPLICATIONS FOR PRACTICE: Low-kilovolt imaging with copper prefiltration provides a superior trade-off between dose reduction and image quality compared to tin-filtered cone-beam CT scan protocols with higher tube voltage.

Detection of thrombosis in microvessels with indocyanine green videoangiography.

Atherosclerosis is a systemic condition that is responsible for many diseases, and becomes a problem in cases where plaques form at several sites. The formation of a thrombotic embolus may jeopardise vascular operations, including microvascular anastomoses in replantation procedures or free tissue transfers. A mobile imaging tool for the detection of thrombosis preoperatively or intraoperatively would be valuable. An intimal injury, simulating removal of atherosclerotic plaques, was made microsurgically in 60 rat aortas, and results were analysed macroscopically, histologically, and with intraoperative indocyanine green (ICG) videoangiography immediately postoperatively. The Spearman and Pearson correlation tests were used to compare the three techniques. The sensitivity and specificity of ICG videoangiography was calculated in relation to both macroscopic and histological results. Detection of thrombosis was possible in 25 cases, and in 18 cases no thrombosis was correctly diagnosed by all methods used. In 31 of 60 specimens formation of thrombus was detected histologically, and in 29 of 60 examinations it was detected clinically, which yielded a correlation of 93.5% between the two examinations. Macroscopic analysis correlated better with ICG videoangiography (sensitivity 86.2% and specificity 64.5%) than histological observations (sensitivity 80.6% and specificity 62.1%). There was a significant correlation among all comparisons (each p≤0.001) with correlation indexes of 0.94, 0.52, and 0.44 for macroscopic/histological, clinical/ICG videoangiographic, and ICG videoangiographic/histological results, respectively. Our results show that ICG videoangiography is an important method for the detection of formation of acute thrombi and may be an important tool in vascular procedures.

Influence of venous stasis on survival of epigastric flaps in rats.

Venous congestion results in tissue damage and remains the most common reason for failure of transfer of microvascular free flaps if it is not recognised early. The purpose of this study was to measure the critical duration of venous congestion and the resultant survival of flaps according to the duration of venous stasis. A standard epigastric flap was raised and repositioned in 35 rats, seven of which acted as controls. The superficial inferior epigastric vein was fully occluded for four, five, six, or seven hours in the rest (n=7 each group). Subsequently, the rats were monitored for one week, and the resultant necrotic areas were photographed. After five, six, and seven hours of venous stasis, the incidence and area of necrosis were significantly increased (p=0.04 in each) above that of the control. The degree of necrosis after seven hours of venous stasis was significantly greater than that after four or five hours (p=0.01 and 0.02, respectively). The duration of venous congestion is therefore a potential risk for the survival of free flaps, as it results in operative complications and may jeopardise the whole procedure. After a critical period of venous stasis we reach a point of no return, and any attempt to salvage the compromised flap will be in vain. Based on these results, we think that monitoring by an experienced surgeon at intervals of no longer than three hours is essential for the successful salvage of venous congestion in microvascular free flaps.

A preclinical Talbot-Lau prototype for x-ray dark-field imaging of human-sized objects.

PURPOSE: Talbot-Lau x-ray interferometry provides information about the scattering and refractive properties of an object - in addition to the object's attenuation features. Until recently, this method was ineligible for imaging human-sized objects as it is challenging to adapt Talbot-Lau interferometers (TLIs) to the relevant x-ray energy ranges. In this work, we present a preclinical Talbot-Lau prototype capable of imaging human-sized objects with proper image quality at clinically acceptable dose levels. METHODS: The TLI is designed to match a setup of clinical relevance as closely as possible. The system provides a scan range of 120 × 30 cm2 by using a scanning beam geometry. Its ultimate load is 100 kg. High aspect ratios and fine grid periods of the gratings ensure a reasonable setup length and clinically relevant image quality. The system is installed in a university hospital and is, therefore, exposed to the external influences of a clinical environment. To demonstrate the system's capabilities, a full-body scan of a euthanized pig was performed. In addition, freshly excised porcine lungs with an extrinsically provoked pneumothorax were mounted into a human thorax phantom and examined with the prototype. RESULTS: Both examination sequences resulted in clinically relevant image quality - even in the case of a skin entrance air kerma of only 0.3 mGy which is in the range of human thoracic imaging. The presented case of a pneumothorax and a reader study showed that the prototype's dark-field images provide added value for pulmonary diagnosis. CONCLUSION: We demonstrated that a dedicated design of a Talbot-Lau interferometer can be applied to medical imaging by constructing a preclinical Talbot-Lau prototype. We experienced that the system is feasible for imaging human-sized objects and the phase-stepping approach is suitable for clinical practice. Hence, we conclude that Talbot-Lau x-ray imaging has potential for clinical use and enhances the diagnostic power of medical x-ray imaging.

Influence of possible predictor variables on the outcome of primary oral squamous cell carcinoma: a retrospective study of 392 consecutive cases at a single centre.

The successful treatment of oral squamous cell carcinoma (OSCC) depends on the treatment strategy. The prognosis is most often linked to the stage at initial presentation, but the effect of patient-related parameters on overall survival remains uncertain. In this study, 392 consecutive cases of OSCC seen between 2007 and 2013 at a single centre were analyzed retrospectively. Overall survival was assessed and univariate and multivariate Cox proportional hazards regression was used to identify associations between possible tumour-specific and patient-related variables and survival. The 5-year overall survival rate of the 392 patients (T stage 1-4) was 62.5%. Univariate analysis showed that sex, age, T stage, N stage, Union for International Cancer Control (UICC) stage, American Society of Anesthesiologists (ASA) status, operating time >400min, and length of in-patient stay >15 days were significantly associated with overall survival (all P<0.05). Tumour location, alcohol abuse, and smoking were found not to have a significant influence (all P>0.05). Age, T, N, and M stages, UICC stage, residual tumour status, recurrence, ASA status, and operating time >400min were found to have a significant influence on overall survival in the multivariate analysis (each P<0.05). These findings confirm that postoperative survival does not depend only on tumour-related characteristics. ASA status needs to be considered in treatment planning, as it significantly predicts patient survival.

Analysis of computer-aided techniques for virtual planning in nasoalveolar moulding.

We compared two methods of planning virtual alveolar moulding as the first step in nasoalveolar moulding to provide the basis for an automated process to fabricate nasoalveolar moulding appliances by using computer-assisted design and computer-aided manufacturing (CAD/CAM). First, the initial intraoral casts taken from seven newborn babies with complete unilateral cleft lip and palate were digitised. This was repeated for the target models after conventional nasoalveolar moulding had been completed. The initial digital model for each patient was then virtually modified by two different modelling techniques to achieve the corresponding target model: parametric and freeform modelling with the software Geomagic(®). The digitally-remodelled casts were quantitatively compared with the actual target model for each patient, and the comparison between the two modified models and the target model showed that freeform modelling of the initial cast was successful (mean (SD) deviation n=7, +0.723 (0.148) to -0.694 (0.157)mm) but needed continuous orientation and was difficult to automate. The results from the parametric modelling (mean (SD) deviation, n=7, +1.168 (0.185) to -1.067 (0.221)mm) were not as good as those from freeform modelling. During parametric modelling, we found some irregularities on the surface, and transverse growth of the maxilla was not accounted for. However, this method seems to be the right one as far as automation is concerned. In addition, an external algorithm must be implemented because the function of the commercial software is limited.

Flow analyses of microvascular bifurcation using laser Doppler anemometry.

INTRODUCTION: Vascular surgery affects, among other factors, vessel geometry and might result in significant flow changes. For this reason a basic understanding of flow behavior at bifurcations plays an important role for microsurgeons. The aim of the present work was to establish an experimental model that enables rheological analyses of microvascular techniques. METHODS: Laser Doppler anemometer (LDA) measurements in a total of four cross-sections of a true-to-scale silicone model were performed. The model was installed in a circulatory experimental setup that simulates the physiologic human blood flow. The flow velocity data measured with the LDA system was processed and analyzed with an image-processing system. RESULTS: The flow curve at each cross-section was recorded for sevem cycles. A physiologic flow separation at bifurcational level was seen. Maximal and minimal horizontal velocities of all measurement points were between 0.32 and -0.15 m/s. No signs of turbulentlike flow were seen in the cross-sections distal to the bifurcation. A total, centrally located backflow in the diastolic phases in all four cross-sections was registered, resembling an oscillatorylike flow. CONCLUSIONS: The LDA analysis represents a valid experimental method for rheological evaluation of microvessels. Due to its unique high spatial and temporal resolution, it represents a worthwhile alternative to other flow investigations.