Stereotactic radiosurgery for brain arteriovenous malformations: quantitative MR assessment of nidal response at 1 year and angiographic factors predicting early obliteration

Introduction We investigated the role of magnetic resonance angiography (MRA) in the early follow-up of patients after stereotactic radiosurgery (STRS) for cerebral arteriovenous malformations (AVMs) and determined the influence of individual morphological factors of AVMs in early response to treatment.Methods A group of 40 patients (41 AVMs) consented to a dedicated 1.5-T MR protocol 12 months after receiving STRS for a brain AVM. In addition to standard spin echo sequences, 3-D contrast-enhanced sliding interleaved Ky MRA (CE-SLINKY) and dynamic time-resolved subtraction angiography (MR-DSA) were performed. Nidal volumes were calculated using CE-SLINKY data in patients with a persisting arteriovenous shunt. Planning angiographic data was investigated in all 40 patients. The following AVM factors were used in the statistical analysis to determine their role in nidus obliteration: (1) maximum linear dimension, (2) nidal volume, (3) AVM location (4) nidal morphology, (5) venous drainage, (6) “high-flow angiographic change”, (7) prior embolization, and (8) dose reduction.Results Complete nidal obliteration was found in 9 patients, 26 showed greater than 50% nidal reduction and 6 had less than 50%. Two AVM factors, venous drainage and AVM location, were found to significantly correlate with rate of obliteration.Conclusion We successfully demonstrated the use of MRA to quantitatively assess the response of AVMs to STRS. Two AVM factors, venous drainage and AVM location were found to correlate with rate of obliteration prior to the application of the Bonferroni correction, but if this more rigorous statistical test was applied then none of the factors was found to be significant.     

Brain arteriovenous malformations: assessment with dynamic MR digital subtraction angiography

BACKGROUND AND PURPOSE: Conventional catheter angiography (CCA) is the current reference standard for the diagnosis, assessment, and management of pial brain arteriovenous malformations (AVMs). The purpose of this study was to develop an MR angiographic technique that produces dynamic images comparable to those provided by CCA and to apply the technique to the investigation of pial brain AVMs. METHODS: Twenty patients with brain AVMs referred for stereotactic radiosurgery were recruited. All patients had CCA performed on a 1.5-T superconducting system. Sixty images were obtained at a rate of one image per second. Slices were orientated to produce Towne, lateral, and anteroposterior projections. A set of mask images was taken and then a series during the passage of a bolus of contrast material. MR examinations were assessed independently by neuroradiologists blinded to the conventional catheter angiographic findings. RESULTS: The nidus of the AVMs was depicted in 19 of the 20 patients, and correlation with CCA was excellent for measurements of maximum diameter. Venous drainage was correctly assessed in 18 of 19 cases. CONCLUSION: MR digital subtraction angiography shows promise as a noninvasive, dynamic angiographic tool for planning stereotactic radiosurgery of AVMs already delineated by catheter angiography. At present, it suffers from temporal and spatial resolution, which impede the assessment of some brain AVMs.     

Commissioning of an intra-operative US guided prostate HDR system integrating an EM tracking technology

PURPOSEUltrasound-based planning for high-dose-rate prostate brachytherapy is commonly used in the clinic, mainly because it offers fast real-time image-guided capability at a relatively low cost. The main difficulty with US planning is the catheter reconstruction due to artefacts (from multiple catheters) and echogenicity. Electromagnetic tracking (EMT) system offers a fast and accurate solution for automatic reconstruction of catheters using the EMT technology. In this study, the commissioning and performance evaluation of the new real-time prostate high-dose-rate brachytherapy investigational system from Philips Disease Management Solutions integrating EMT was performed before its clinical integration.METHOD AND MATERIALSThe Philips’ clinical investigational system includes a treatment planning software (TPS) that was commissioned based on AAPM TG53 and TG56 recommendations for the use of TPS in brachytherapy. First, the CIRS - model 045A - QA phantom was used to evaluate the ultrasound (US) image quality and 3D image handling. Distances, volumes, and dimensions of the structures inside the phantom were measured and compared to the actual values. The calibration reproducibility and accuracy of the electromagnetic (EM) sensor used to track the US probe (rotation and translation) were performed using a specifically designed QA tool mounted on the probe and immersed in a salted water tank. This was performed for 3 different B&K 8848 US probes to evaluate the sensitivity of EM calibration to the probe geometric properties (manufacturing process). The new TPS performance was compared to that in OncentraBrachy (OcB) V4.5.5 (Elekta) using 30 clinical cases as part of a retrospective study. Following the system commissioning, clinical workflows were explored; tests were performed with the brachytherapy team on phantoms and finally implemented in the clinic.RESULTSUS image quality evaluation showed a mean difference with actual dimensions (lengths, widths and distances) of 0.4 mm (±0.3 mm) and mean difference in volume sizes of 0.2 cc (±0.2 cc). Then, the calibration of the US-to-EM coordinate system was performed for 3 different probes. For each probe, 3 measurements were acquired for every position of the calibration tool and measurements were repeated 3 times for a total of 27 measurements per probe per plane. The error was slightly higher in transverse mode compared to sagittal mode with mean values of 0.6 ± 0.2 mm and 0.3 ± 0.1 mm respectively. 30 clinical cases were used to compare the new TPS performance to OcB (IPSA). Optimized plans obtained with both systems were all clinically acceptable, but the plans from the Philips system have slightly higher V150% values, V200% values and dose to organs at risk. In the case of organs at risk, plans could have been manually modified to reduce the dose. Philips’ system had a larger number of active dwell positions and longer treatment times.CONCLUSIONSThe first clinical version of Philips’ system was proven to be stable, accurate and precise. The fully integrated EM tracking technology opens the way for automated catheter reconstruction and on-the-fly dynamical replanning.     

Automated volumetry at CT colonography: a phantom study

RATIONALE AND OBJECTIVES: To assess the performance of a computer-aided detection (CAD) algorithm for measuring polyp-like structures on CT colonography (CTC) images of a phantom. MATERIALS AND METHODS: We constructed a Plexiglas phantom to which we affixed a series of idealized Plexiglas polyp-like objects, including spheres and hemispheres. We imaged the phantom in a four-channel detector CT scanner at a 1.3 mm slice thickness with a reconstruction interval of 0.6 mm, using combinations of 100 mAs, 30 mAs, horizontal and vertical orientation. For each set of CT images, the interior surface of the phantom was segmented. The CAD algorithm was applied to the resulting surface to identify the polypoid regions of interest and to calculate their volume and maximum linear dimension. Calculated values were then compared with actual values to yield percent error in each measurement. RESULTS: The mean error in volume for the subgroups of spheres and hemispheres was 3% and 5% respectively. Mean error in linear dimension was approximately 2% for both shape subgroups. All CAD-calculated values were closely correlated with their respective actual values. Parameter selection did not significantly affect the accuracy of the calculated measurements. CONCLUSIONS: Our CAD software accurately measured the greatest linear dimension and the volume of each of the polyp-like structures in our phantom. Results were largely independent of phantom orientation and the CT exposure factors.     

Accuracy of measurements of mandibular anatomy and prediction of asymmetry in panoramic radiographic images

OBJECTIVES: Measurements of ideally positioned and systematically mis-positioned skulls were used to evaluate errors in linear measurements and symmetry ratios made with panoramic X-ray images. METHODS: Digital panoramic images of 30 skulls placed in ideal, shifted and rotated positions, were assessed by measuring distances between anatomic points and fiducial references. Differences between photographic measurements (control) and radiographic measurements were compared. Horizontal measurements included a 20 mm wire and the distance from gonion to mental foramen (G-MF). Vertical distances measured included a 40 mm wire, condyle to sigmoid notch length, and condyle to gonion (posterior mandibular height or PMH). A relative symmetry ratio comparing the difference between right and left PMH was also calculated. Distances measured in panoramic images were corrected using the left vertical wire distance or the panoramic unit's stated magnification factor (1.25x). RESULTS: Greatest differences were noted for horizontal measurements and shifted skull positions. Use of an arbitrary magnification correction was consistently less accurate than use of an internal calibration and resulted in general underestimation of actual dimensions. Measures of PMH varied significantly from expected values for each of the three skull positions (P<0.005). Panoramic accuracy for detecting asymmetry was 67% for ideal, 70% for rotated, and 47% for shifted skull positions when an internal reference was used. CONCLUSIONS: Panoramic radiographs should be used with caution in making absolute measurements or relative comparisons. Even when internal fiducial calibration for image distortion of anatomy is used, measurements such as those assessing posterior mandibular facial symmetry may be unreliable.     

Quantitative coronary arteriography: design and validation

The authors assessed the performance of an automatic and rapid coronary quantification method by evaluating its accuracy in a stenosis phantom. Measurements were obtained with a lucite phantom with 2-, 3-, and 4-mm vessel diameters and concentric stenoses of 33%, 50%, 67%, and 75%. Direct digital angiographic images as well as 10 X 10 spot films and 35-mm cine angiography films were acquired with and without structural noise and mask subtraction. The films were digitized with magnification factors of one and two. An interactive analysis program was used to automatically determine the vessel edges with a Gaussian fit to the cross-sectional density profiles perpendicular to the center line of the vessel. Relative changes of the densitometric cross-sectional area along the vessel were used to assess the percentage of stenosis. Densitometric measurements were comparable in both digital and cine angiograms (r = .99 and r = .98, respectively); however, diameter measurements showed a higher variability and were dependent on the amount of magnification applied to the images.     

Operation and calibration of the novel PTW 1600SRS detector for the verification of single isocenter stereotactic radiosurgery treatments of multiple small brain metastases

Objectives:The aim of this work was to evaluate the operation of the 1600SRS detector and to develop a calibration procedure for verifying the dose delivered by a single isocenter stereotactic radiosurgery (SRS) treatment of small multiple brain metastases (BM).Methods:14 clinical treatment cases were selected with the number of BM ranging from 2 to 11. The dosimetric agreement was investigated between the calculated and the measured dose by an OCTAVIUS 1600SRS array detector in an OCTAVIUS 4D phantom equipped with dedicated SRS top. The cross-calibration procedure deviated from the manufacturer’s as it applied field sizes and dose rates corresponding to the volumetric modulated arc therapy segments in each plan.Results:Measurements with a plan specific cross-calibration showed mean ± standard deviation (SD) agreement scores for cut-off values 50%, 80%, 95%, of 98.6 ± 1.7%, 96.5 ± 4.6%, 97.3 ± 4.4% for the 6 MV plans respectively, and 98.6 ± 1.5%, 96.6 ± 4.0% 96.4 ± 6.3%, for the 6 MV flattening filter free (FFF) plans respectively. Using the default calibration procedure instead of the plan specific calibration could lead to a combined systematic dose offset of 4.1% for our treatment plans.Conclusion:The 1600SRS detector array with the 4D phantom offers an accurate solution to perform routine quality assurance measurements of single isocenter SRS treatments of multiple BM. This work points out the necessity of an adapted cross-calibration procedure.Advances in knowledge:A dedicated calibration procedure enables accurate dosimetry with the 1600SRS detector for small field single isocenter SRS treatment of multiple brain metastases for a large amount of BM.     

Automated calibration in vascular X-ray images using the accurate localization of catheter marker bands

RATIONALE AND OBJECTIVES: To develop a new automated calibration method for vessel measurements in vascular x-ray images. METHODS: Radiopaque marker bands mounted equidistantly on a small catheter were acquired in vitro at five image intensifier (II) sizes in x-ray projection images. The positions of the marker centers were detected by using a Hough transform and were computed at subpixel precision by using either a novel, iterative center-of-gravity approach (CGA) or a symmetry filter. Curve-fitting procedures were used to reject false-positive marker detections and to calculate intermarker distances. The calibration factor was calculated from the true marker distance and the average of the measured distances in pixels. Results were compared statistically with a grid calibration method, which was taken as the gold standard. A simulation study was performed to assess the influence of image noise on the CGA method. RESULTS: The iterative CGA method was convergent and faster than the symmetry-based technique. For four II sizes (17, 20, 25, and 31 cm), the results from the CGA method were not significantly different from the results obtained with grid calibration. For the II size of 38 cm, a significant difference (0.3% of the grid calibration factor) was found; however, this was caused by the quantification error in the image data and was not clinically relevant. In general, the performance of the CGA method improved with increasing signal-to-noise ratio. CONCLUSIONS: A practical new calibration method for small catheter sizes was developed and validated for quantitative vascular arteriography.     

混叠效应对数字化X线影像的影响及其分析

目的 探讨数字X线摄影中混叠效应的产生原因及其对影像质量的影响。方法 使用Kodak CR900系统分别对矩形波测试卡和固定滤线栅成像。测试卡铅条在平行于激光扫描方向和呈45°角的放置方式下分别成像,观察两种影像对分辨率测试卡的显示情况。使滤线栅铅条的方向在平行和垂直于激光扫描方向时分别成像,在显示器上使用不同的放大率对滤线栅影像进行观察,并比较两种影像外观的差异。结果 测试卡影像上,3.93线对/mm以上频率的铅条影无法相互分辨,因此尼奎斯特频率为3.93 LP/mm。但在测试卡45°放置的影像中,频率为4.86 LP/mm的铅条仍能相互分辨。滤线栅铅条平行于成像板的激光扫描方向时,最终影像中显示出明显的条纹影。在显示器上使用不同的放大率观察时,栅条形成的条纹影宽度和方向都发生明显变化。铅条与激光扫描方向垂直时影像中的条纹影显著减弱。结论 CR应用中混叠效应会对数字影像产生不利影响,应根据设备的极限分辨率选择适当的固定滤线栅,栅频率应大于尼奎斯特频率。在摄影中,滤线栅的铅条方向应与成像板的激光扫描方向相垂直。在显示器上观察固定滤线栅摄影影像时,建议使用原始图像的整数倍的放大率。     

Accuracy of MRI-guided stereotactic thalamic functional neurosurgery

Our goal was to evaluate the accuracy of stereotactic technique using MRI in thalamic functional neurosurgery. A phantom study was designed to estimate errors due to MRI distortion. Stereotactic mechanical accuracy was assessed with the Suetens-Gybels-Vandermeulen (SGV) angiographic localiser. Three-dimensional MRI reconstructions of 86 therapeutic lesions were performed. Their co-ordinates were corrected from adjustments based on peroperative electrophysiological data and compared to those planned. MR image distortion (maximum: 1 mm) and chemical shift of petroleum oil-filled localiser rods (2.2 mm) induced an anterior target displacement of 2.6 mm (at a field strength of 1.5 T, frequency encoding bandwidth of 187.7 kHz, on T1-weighted images). The average absolute error of the stereotactic material was 0.7 mm for anteroposterior (AP), 0.5 mm for mediolateral (ML) and 0.8 mm for dorsoventral (DV) co-ordinates (maximal absolute errors: 1.6 mm, 2.2 mm and 1.7 mm, respectively; mean euclidean error: 1 mm). Three-dimensional MRI reconstructions showed an average absolute error of 0.8 mm, 0.9 mm and 1.9 mm in AP, ML and DV co-ordinates, respectively (maximal absolute errors: 2.4 mm, 2.7 mm and 5.7 mm, respectively; mean euclidean error: 2.3 mm). MRI distortion and chemical-shift errors must be determined by a phantom study and then compensated for. The most likely explanation for an average absolute error of 1.9 mm in the DV plane is displacement of the brain under the pressure of the penetrating electrode. When this displacement is corrected for by microelectrode recordings and stimulation data, MRI offers a high degree of accuracy and reliability for thalamic stereotaxy. Received: 22 September 1998 Accepted: 1 January 1999     

Magnetic Catheter Manipulation in the Interventional MR Imaging Environment

PurposeTo evaluate deflection capability of a prototype endovascular catheter, which is remotely magnetically steerable, for use in the interventional magnetic resonance (MR) imaging environment.Materials and MethodsCopper coils were mounted on the tips of commercially available 2.3–3.0-F microcatheters. The coils were fabricated in a novel manner by plasma vapor deposition of a copper layer followed by laser lithography of the layer into coils. Orthogonal helical (ie, solenoid) and saddle-shaped (ie, Helmholtz) coils were mounted on a single catheter tip. Microcatheters were tested in water bath phantoms in a 1.5-T clinical MR scanner, with variable simultaneous currents applied to the coils. Catheter tip deflection was imaged in the axial plane by using a “real-time” steady-state free precession MR imaging sequence. Degree of deflection and catheter tip orientation were measured for each current application.ResultsThe catheter tip was clearly visible in the longitudinal and axial planes. Magnetic field artifacts were visible when the orthogonal coils at the catheter tip were energized. Variable amounts of current applied to a single coil demonstrated consistent catheter deflection in all water bath experiments. Changing current polarity reversed the observed direction of deflection, whereas current applied to two different coils resulted in deflection represented by the composite vector of individual coil activations. Microcatheter navigation through the vascular phantom was successful through control of applied current to one or more coils.ConclusionsControlled catheter deflection is possible with laser lithographed multiaxis coil-tipped catheters in the MR imaging environment.     

Vessel size estimation in peripheral artery interventions: are angiographic measurements reliable?

PURPOSE: To describe and evaluate a new technique for angiographic measurement of arterial diameters and to make a comparison with other common techniques. MATERIAL AND METHODS: The Angiometer has a radiopaque metal body with six cylindrical segments of varying diameter. Arterial diameter is estimated by visually relating the vessel to these segments. The measurements (method A) were compared: to measuring in relation to a ruler on the table-top by means of compasses (B), to an automated measurement technique (quantitative angiography) utilizing calibration to a catheter of known diameter (C), and to a computer-based distance measurement using the ruler on the table-top as reference (D). Twenty-five patients were studied. Each method was used twice by each of two independent observers. A phantom with four drilled holes, filled with contrast agent, was also studied. RESULTS: The coefficient of variation was highest for method C and lowest for method A. Correlations between readings were highest for method A and lowest for method C. Mean diameter values were highest for method A and lowest for methods B and D. In the phantom experiments, sizes were overestimated by between 5% and 9% with method A, and underestimated by between 4% and 27% with the other methods. CONCLUSION: In terms of reproducibility and accuracy, the proposed method compares favorably with alternative methods.     

Application of Time-Resolved 3D Digital Subtraction Angiography to Plan Cerebral Arteriovenous Malformation Radiosurgery

BACKGROUND AND PURPOSE:Time-resolved 3D-DSA (4D-DSA) enables viewing vasculature from any desired angle and time frame. We investigated whether these advantages may facilitate treatment planning and the feasibility of using 4D-DSA as a single imaging technique in AVM/dural arteriovenous fistula radiosurgery.MATERIALS AND METHODS:Twenty consecutive patients (8 dural arteriovenous fistulas and 12 AVMs; 13 men and 7 women; mean age, 45 years; range, 18–64 years) who were scheduled for gamma knife radiosurgery were recruited (November 2014 to October 2015). An optimal volume of reconstructed time-resolved 3D volumes that defines the AVM nidus/dural arteriovenous fistula was sliced into 2D-CT-like images. The original radiosurgery treatment plan was overlaid retrospectively. The registration errors of stereotactic 4D-DSA were compared with those of integrated stereotactic imaging. AVM/dural arteriovenous fistula volumes were contoured, and disjoint and conjoint components were identified. The Wilcoxon signed rank test and the Wilcoxon rank sum test were adopted to evaluate registration errors and contoured volumes of stereotactic 4D-DSA and integration of stereotactic MR imaging and stereotactic 2D-DSA.RESULTS:Sixteen of 20 patients were successfully registered in Advanced Leksell GammaPlan Program. The registration error of stereotactic 4D-DSA was smaller than that of integrated stereotactic imaging (P = .0009). The contoured AVM volume of 4D-DSA was smaller than that contoured on the integration of MR imaging and 2D-DSA, while major inconsistencies existed in cases of dural arteriovenous fistula (P = .042 and 0.039, respectively, for measurements conducted by 2 authors).CONCLUSIONS:Implementation of stereotactic 4D-DSA data for gamma knife radiosurgery for brain AVM/dural arteriovenous fistula is feasible. The ability of 4D-DSA to demonstrate vascular morphology and hemodynamics in 4 dimensions potentially reduces the target volumes of irradiation in vascular radiosurgery.

Radiosurgery is an effective treatment alternative for cerebral arteriovenous malformations^1–4 and intracranial dural arteriovenous fistulas (DAVFs).^5–10 In AVM/DAVF radiosurgery, irradiation is delivered in a single fraction stereotactically to only the nidus of an AVM or fistula of a DAVF.Our current clinical practice of AVM/DAVF radiosurgery, integrated stereotactic imaging (MR imaging/MRA and x-ray digital subtraction angiography) is used for nidus/fistula delineation. The integrated multiple-stop stereotactic imaging is considered the reference imaging for AVM/DAVF radiosurgery. MR imaging is superior in delineating radiosurgical target in 3D, and DSA excels in defining the hemodynamics of AVM/AVF and differentiating the nidus/fistula from feeding arteries and draining veins of AVM/DAVF.¹¹ However, the role of DSA as a projective 2D representation of 3D structures in defining the nidus is limited, especially when the AVM is large and the nidus has an oblique long axis relative to the orthogonal DSA projections.¹² Moreover, for AVMs that undergo partial embolization before radiosurgery, the nidus may become intricate, and it may be difficult to define its morphology on 2D-DSA or MR imaging/MRA.¹³ Recently, it was shown that conebeam CT 3D angiography can generate images of a high spatial resolution that depict low-flow nidal compartments better than both DSA and MR imaging, though it lacks temporal information.¹⁴ While our current practice has achieved high tissue conformity in AVM radiosurgery and good therapeutic results,¹⁵ an alternative technique, if chosen, must be able to provide panoramic morphological and hemodynamic evaluation of nidi/fistulas in 1 stop.In contrast to 2D-DSA, fully time-resolved 3D-DSA, also known as 4D-DSA, provides a series of time-resolved 3D volumes that correspond to contrast dynamics with a C-arm-based imaging system.¹⁶ While the reconstruction of a 4D-DSA image from a single rotational image acquisition has some inherited technical difficulties, as mentioned by Royalty,¹⁷ the volumetric vascular morphology and bolus-arrival patterns reconstructed from 4D-DSA algorithms are validated.¹⁷ An animal study based on a canine model also demonstrated that 4D-DSA is capable of delineating vasculature effectively.¹⁸ Small-series studies also suggested that 4D-DSA enhances the ability to visualize the vascular anatomy of an AVM.^19,20 Accordingly, 4D-DSA enables evaluating feeding arteries, nidi, and draining veins in sequential imaging in 3D and eliminates the issue of overlapped vasculatures.In this study, we compare the registration errors of stereotactic 4D-DSA with those of integrated stereotactic imaging and the vascular anatomy of AVMs and DAVFs depicted by 4D-DSA volumes with the planned dose contours for each recruited patient and evaluate whether 4D-DSA may facilitate the planning of AVM/DAVF radiosurgery by minimizing the irradiation volume as 1-stop imaging.     

Quantitative contrast-enhanced computed tomography: is there a need for system calibration?

The purpose of the study was to perform phantom studies to assess the impact of computed tomography (CT) system variability on quantitative measurements of contrast enhancement. A phantom containing tubes of contrast material at dilutions of 120, 1:35, 1:50, 1:100 and 1:200 arranged in air or water was imaged using 11 CT systems at 9 institutions. All systems had undergone routine calibration against air and water in accordance with the manufacturers’ recommendations. For a given tube voltage, the relationship between the iodine concentration and CT attenuation value on a single system varied by 17 to 24% over 46–48 weeks. The coefficients of variance for iodine calibration factors across different CT systems were 8.9% in air and 5.1% in water. Calibration of individual CT systems for iodine response is required to allow comparison of quantitative measurements of contrast enhancement across different institutions. Using the iodine calibration factor to express contrast enhancement as iodine concentration would facilitate the universal application of diagnostic enhancement thresholds, especially if the necessary calculations were performed by software installed on the CT console.     

The efficacy of particulate embolization combined with stereotactic radiosurgery for treatment of large arteriovenous malformations of the brain.

PURPOSETo evaluate the efficacy of combined particulate embolization and single-stage stereotactic radiosurgery in the treatment of large arteriovenous malformations (AVMs) of the brain.METHODSTwenty-four patients with large brain AVMs (diameter > 3.0 cm; volume > 14 cm3), who had previously undergone particulate embolization and stereotactic radiosurgery, were retrospectively evaluated 2 or more years after radiosurgery.RESULTSIn 12 (50%) of these patients there was complete AVM obliteration, comparing favorably with a 58% obliteration rate in a group of AVMs having a 4- to 10-cm3 volume, treated by radiosurgery alone. Recanalization of embolized, but not radiated, AVM segments was identified in 3 (12%) patients. However, long-term occlusion was demonstrated in the embolized portions of most AVMs subsequently treated by radiosurgery. Complications included 1 (4%) patient with a mild upper extremity paresis after radiosurgery and 2 (8%) patients with transient neurologic deficits after embolization.CONCLUSIONCombined embolization and stereotactic radiosurgery was more efficacious than radiosurgery alone for large brain AVMs. Recanalization after embolization did occur but was a relatively minor cause of treatment failure.     

Measurement accuracy of sonographic sector scanners

Discrepancies identified in anatomic size measurements in clinical obstetric sonographic studies prompted a study of the accuracy of measurements obtained from sonographic mechanical sector scanners. There were large variations in equipment calibration of the size of the sector scan angle among six clinical sonographic units from four manufacturers, causing transverse measurements to vary from 47% (high) to 9% (low), compared with the true size of a cylindrical plastic phantom. Depth measurements, parallel to the direction of sound penetration, are only velocity dependent and were accurate to within 6%. Transverse size measurements made using mechanical sector scanners should be suspect unless the calibration has been checked using a phantom test object.     

An option for optimising the radiographic technique for horizontal beam lateral (HBL) hip radiography when using digital X-ray equipment

AimTo investigate the optimum technique for the horizontal beam lateral (HBL) hip projection considering image quality and radiation dose.MethodsUsing digital radiography equipment an anthropomorphic phantom was positioned for a HBL projection of the hip. Radiographic exposures were undertaken across a range of acquisition parameters (tube potentials, source to image distances, object to detector distances, with and without an anti-scatter radiation grid/additional copper filtration). Each acquisition combination was imaged three times and the dose area product (DAP) and post-AEC mAs recorded. 168 images were acquired. A single observer evaluated five anatomical areas on all images using a two-alternative force choice technique. The reference image was selected based on the current locally accepted technique. 50 images out of the original 168 were independently assessed by a further four observers to ensure reliability of the results.ResultsImage quality, when comparing all the images to the reference, was improved on in two cases; however the radiation dose had increased. 18 images had equal image quality with some having an 80% reduction in the DAP. In terms of the diagnostic acceptability, 51 were considered acceptable with a lower radiation dose.ConclusionBy optimising acquisition factors for the HBL hip projection the radiation dose to the patient can be reduced. Based on the findings the factors proposed for HBL hip projections are 90 kVp, 135 cm SID, 45 cm ODD, grid and 0.1 mm copper filtration.     

Electromagnetic tracking for catheter reconstruction in ultrasound-guided high-dose-rate brachytherapy of the prostate

PurposeThe accurate delivery of high-dose-rate brachytherapy is dependent on the correct identification of the position and shape of the treatment catheters. In many brachytherapy clinics, transrectal ultrasound (TRUS) imaging is used to identify the catheters. However, manual catheter identification on TRUS images can be time consuming, subjective, and operator dependent because of calcifications and distal shadowing artifacts. We report the use of electromagnetic (EM) tracking technology to map the position and shape of catheters inserted in a tissue-mimicking phantom.Methods and MaterialsThe accuracy of the EM system was comprehensively quantified using a three-axis robotic system. In addition, EM tracks acquired from catheters in a phantom were compared with catheter positions determined from TRUS and CT images to compare EM system performance to standard clinical imaging modalities. The tracking experiments were performed in a controlled laboratory environment and also in a typical brachytherapy operating room to test for potential EM distortions.ResultsThe robotic validation of the EM system yielded a mean accuracy of <0.5 mm for a clinically acceptable field of view in a nondistorting environment. The EM-tracked catheter representations were found to have an accuracy of <1 mm when compared with TRUS- and CT-identified positions, both in the laboratory environment and in the brachytherapy operating room. The achievable accuracy depends to a large extent on the calibration of the TRUS probe, geometry of the tracked devices relative to the EM field generator, and locations of surrounding clinical equipment. To address the issue of variable accuracy, a robust calibration algorithm has been developed and integrated into the workflow. The proposed mapping technique was also found to improve the workflow efficiency of catheter identification.ConclusionsThe high baseline accuracy of the EM system, the consistent agreement between EM-tracked, TRUS- and CT-identified catheters, and the improved workflow efficiency illustrate the potential value of using EM tracking for catheter mapping in high-dose-rate brachytherapy.     

Effect of gap-filling technique and gap location on linear and nonlinear calculations of motion during locomotor activities

BackgroundMarker occlusion during camera-based movement analysis is common. Different interpolation techniques are available for estimating location of missing marker trajectories.Research questionWhat is the effect of gap location and interpolation technique on linear and nonlinear measures for a given kinematic time series?MethodsKinematic data were recorded during motor-assisted elliptical training and treadmill walking. Gap-filling techniques (i.e., Cubic, Makima, Autoregressive, Nearest Neighbor, and No Interpolation) and gap locations experimentally applied to each cycle across initially complete time series (Gap 1: local minimum and maximum peaks; Gap 2: maximum peaks; Gap 3: maximum peaks at negative slope; Gap 4: random locations) were examined during linear (Maxima and Minima joint angles) and nonlinear [maximum Lyapunov exponent (LyE)] measures.ResultsGap-filling technique and gap location influenced values calculated for linear and nonlinear measures of joint motions. When referenced to the gold standard (original data series without gaps), across all joints studied the average % error of Maxima and Minima joint angles and LyE % error were lower when applying Cubic, Makima, Autoregressive, and Nearest Neighbor techniques compared to No Interpolation (p < 0.0001). The % error of Maxima joint angles was lower for Gaps 1, 3, and 4 compared to Gap 2 (p = 0.0003), while % error of Minima joint angles was lower for Gaps 2 and 3, compared to Gaps 1 and 4 (p < 0.0001). An interaction between gap-filling technique and gap location was identified for LyE % error, in which Gap 4 % error was significantly greater during No Interpolation compared to other gap-filling techniques (p < 0.0001).SignificanceFindings can guide selection of appropriate techniques to manage missing kinematic data points in camera-based motion analysis time series. Gap-filling techniques significantly reduced error in calculating select linear and nonlinear measures of variability, with Cubic most consistently resulting in the greatest reduction in error.     

Assessment of organ volume with different techniques using a living liver model

The purpose of this study was to compare different techniques for the estimation of liver volume, and to evaluate errors associated with volume estimation techniques based on linear measurements. Fifteen patients with focal liver lesion underwent spiral CTA for preoperative evaluation. The scan protocol was: collimation 3 mm; rotation time 0.75 s; pitch 2; and reconstruction index 1 mm. Reconstructed images were sent to a workstation running on a NT platform equipped with post-processing software allowing 3D reconstructions. Linear measurements and volume estimation through manual segmentation were obtained with preset window and magnification. Volume was calculated from linear measures using different equations. With equations based on linear measurements the right lobe was overestimated (mean=+53%; mean error=14.7%), the second and third segments were underestimated (mean=–47%; mean error=43.3%) and the total volume was underestimated (mean=–86%; mean error=36%). The volume calculated by summing the areas of all the sections and multiplying the result by the increment was not significantly different from the volume estimated using the manual volumetric segmentation technique. Volume estimation obtained through linear measurements is not reliable to appraise the volume of irregular-shaped solids, even assuming the prevalence of a particular morphology. Electronic Publication