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BACKGROUND AND PURPOSE: Aneurysm size and neck measurements are important for treatment decisions. The introduction of 7T magnetic resonance angiography (MRA) led to new possibilities assessing aneurysm morphology and flow due to the higher signal-to-noise ratio. However, it is unknown if the size measurements on 7T MRA are similar to those on the standard 3T MRA. This study aimed to compare aneurysm size measurements between 7T and 3T MRA.METHODS: We included 18 patients with 22 aneurysms who underwent both 3T and 7T MRA. Three acquisition protocols were compared: 3T time of flight (TOF), 7T TOF, and 7T contrast-enhanced MRA. Each aneurysm on each protocol was measured by at least two experienced neuroradiologists. Subsequently, the differences were evaluated using scatterplots and the intraclass correlation coefficients (ICC) of agreement.RESULTS: There was a good agreement among the neuroradiologists for the height and width measurements (mean ICC: .78-.93); the neck measurements showed a moderate agreement with a mean ICC of .57-.72. Between the MR acquisition protocols, there was a high agreement for all measurements with a mean ICC of .81-.96. Measurement differences between acquisition protocols (0-2.9 mm) were in the range of the differences between the neuroradiologists (0-3.6 mm).CONCLUSION: Our study showed that 7T MRA, both nonenhanced and contrast-enhanced, has a high agreement in aneurysm size measurements compared to 3T. This suggests that 7T is useful for reliable aneurysm size assessment.

Fracture gap and step-off measurements on 2DCT-slices probably underestimate the complex multi-directional features of tibial plateau fractures. Our aim was to develop a quantitative 3D-CT (Q3DCT) fracture analysis of these injuries. CT-based 3D models were created for 10 patients with a tibial plateau fracture. Several 3D measures (gap area, articular surface involvement, 3D displacement) were developed and tested. Gaps and step-offs were measured in 2D and 3D. All measurements were repeated by six observers and the reproducibility was determined by intra-class correlation coefficients. Q3DCT measurements demonstrated a median gap of 5.3 mm, step-off of 5.2 mm, gap area of 235 mm2, articular surface involvement of 33% and 3D displacement of 6.1 mm. The inter-rater reliability was higher in the Q3DCT than in the 2DCT measurements for both the gap (0.96 vs. 0.81) and step-off (0.63 vs. 0.32). Q3DCT measurements showed excellent reliability (ICC of 0.94 for gap area, 1 for articular surface involvement and 0.99 for 3D displacement). Q3DCT fracture analysis of tibial plateau fractures is feasible and shows excellent reliability. 3D measurements could be used together with the current classification systems to quantify the true extent of these complex multi-directional fractures in a standardized way.

Objective: Supra- and infrarenal aortic neck angulation have been associated with complications after endovascular aortic aneurysm repair. However, a uniform angulation measurement method is lacking and the concept of angulation suggests a triangular oversimplification of the aortic anatomy. (Semi-)automated calculation of curvature along the center luminal line describes the actual trajectory of the aorta. This study proposes a methodology for calculating aortic (neck) curvature and suggests an additional method based on available tools in current workstations: curvature by digital calipers (CDC). Methods: Proprietary custom software was developed for automatic calculation of the severity and location of the largest supra- and infrarenal curvature over the center luminal line. Twenty-four patients with severe supra- or infrarenal angulations (≥45°) and 11 patients with small to moderate angulations (

Aim To determine the effect of using 80 kV tube voltage and a reduced amount of contrast medium on the image quality and radiation dose of computed tomography angiography (CTA) of the abdominal aorta. Materials and methods Patients who were referred for a CTA examination of the abdominal aorta were included in this technical efficacy study. Thirty patients were divided randomly into two groups. Fifteen patients underwent a dual-energy CT (DECT) protocol (Group A). Fifteen patients were scanned with the use of an automated tube potential selection algorithm tool (Group B). In both protocols, a test bolus injection of 10 ml ioversol (350 mg iodine/ml) was used, followed by 20 ml of 1:1 saline-diluted contrast medium. Quantitative analysis comprised determination of the mean attenuation and contrast-to-noise ratio. Qualitative image analysis was performed independently by five radiologists. The estimated radiation dose in terms of CT dose index and effective dose was recorded and compared with a standard 120 kV protocol. Results In Group B, six patients underwent CTA at 80 kV, seven patients underwent CTA at 100 kV and two patients underwent CTA at 120 kV. The mean contrast-enhancement values of Group A (80 kV) and the 80 kV subgroup of Group B were 16.5% and 27.6% higher compared to the 100 kV subgroup of Group B, these differences were, however, not significant. There were no significant differences in mean image quality between groups. In patients undergoing CTA at 80 kV the effective dose decreased by up to 51.3% compared to a conventional 120 kV CTA protocol. Conclusions The findings of this study support the hypothesis that 80 kV in CTA of the abdominal aorta can reliably be used with only 30 ml contrast medium in total and a 50% reduction in radiation dose. The overall image quality was diagnostically adequate; however, it appeared to be suboptimal in patients with a BMI above 28 kg/m 2 .

Objective Endovascular aortic sealing (EVAS) with the Nellix endosystem (Endologix, Irvine, CA, USA) is a new concept to treat infrarenal abdominal aortic aneurysms (AAAs). By sealing the aneurysm, potential endoleaks may be avoided. Early results of EVAS are good, but no data have been published regarding peri-procedural changes in aortoiliac anatomy. In this study, 27 consecutive patients who underwent elective EVAS repair of an AAA were reviewed. Method Specific AAA (diameter, length from renal arteries to aortic bifurcation, supra- and infrarenal neck angulation, AAA volume, thrombus volume, and flow lumen volume), and iliac artery characteristics (length, angulation, location of most severe angulation with reference to the origin of the common iliac artery) were determined from pre- and post-procedural reconstructed computed tomography angiograms. Results No type I or II endoleaks were seen at 30 day follow up. Total AAA volume, suprarenal and infrarenal angulation, as well as aortic neck diameter did not change significantly post-EVAS. AAA flow lumen increased significantly (mean difference −4.4 mL, 95% CI 2.0 to −8.6 mL) and AAA thrombus volume decreased (mean difference 3.2 mL, 95% CI 2.0 to −1.1 mL). AAA length (125.7 mm vs. 123.1 mm), left common iliac artery length (57.6 mm vs. 55.3 mm), and right and left maximum iliac artery angulation (right 37.4° vs. 32.2°; left: 43.9° vs. 38.4°) were reduced significantly and the location of maximum angulation was further from the iliac artery origin post-EVAS, suggesting slight straightening of the aortoiliac anatomy. Conclusion Most aortoiliac anatomic characteristics remained unchanged post-EVAS. Filling of the endobags to a pressure of 180 mmHg may lead to lost thrombus volume in some patients, probably because liquid is squeezed into lumbar or the inferior mesenteric artery. The absolute differences in pre- and post-EVAS aortoiliac lengths were small, so pre-operative sizing is accurate for determining stent length.

Purpose: To examine the influence of device positioning and infrarenal neck diameter on flow patterns in the Nellix endovascular aneurysm sealing (EVAS) system. Methods: The transition of the aortic flow lumen into two 10-mm-diameter stents after EVAS creates a mismatched area. Flow recirculation may affect local wall shear stress (WSS) profiles and residence time associated with atherosclerosis and thrombosis. To examine these issues, 7 abdominal aortic aneurysm flow phantoms were created, including 3 unstented controls and 3 stented models with infrarenal neck diameters of 24, 28, and 32 mm. Stents were positioned within the instructions for use (IFU). Another 28-mm model was created to evaluate lower positioning of the stents outside the IFU (28-mm LP). Flow was visualized using optical particle imaging velocimetry (PIV) and quantified by time-averaged WSS (TAWSS), oscillatory shear index (OSI), and relative residence time (RRT) in the aorta at the anteroposterior (AP) midplane, lateral midplane, and renal artery AP midplane levels. Results: Flow in the aorta AP midplane was similar in all models. Vortices were observed in the stented models in the lateral midplane near the anterior and posterior walls. In the 32-mm IFU and 28-mm LP models, a steady state of vortices appeared, with varying location during a cycle. In all models, a low TAWSS (−2 Pa) was observed at the anterior wall of the aorta with peak OSI of 0.5 and peak RRT of 104 Pa−1. This region was more proximally located in the stented models. The 24- and 28-mm IFU models showed flow with a higher velocity at the renal artery inflow compared to controls. TAWSS in the renal artery was lower near the orifice in all models, with the largest area in the 24-mm IFU model. OSI and RRT in the renal artery were near zero for all models. Conclusion: EVAS enhances vorticity proximal to the seal zone, especially with lower positioning of the device and in larger neck diameters. Endobags just below the renal artery affect the flow profile in a minor area of this artery in 24- and 28-mm necks, while lower stent positioning does not influence the renal artery flow profile.

Aim To investigate the association between a non-invasive cardiac output (CO) measurement and the scan delay, as derived from a test bolus injection protocol. The secondary objective was to determine which factors affect the relationship between the CO and scan delay. Materials and methods Fifty-five patients referred for a contrast-enhanced (thorax-)abdomen CT examination were included in this feasibility study. A test bolus examination was performed prior to the abdominal CT. During the test bolus injection, the CO of the patient was measured using a non-invasive finger-cuff measurement. Associations were analysed using linear regression analyses. Age, gender, height, weight, and blood pressure were included as potential confounders. Results Linear regression analysis showed a negative and significant association between CO and delay. The regression formula was as follows: scan delay (seconds) = 26.8–1.6 CO (l/min), with a 95% CI between −2.3 and −1.0 (p

Objective Obliteration of collaterals during (endo)vascular treatment of peripheral arterial occlusive disease is considered detrimental. We use a model to calculate maximum collateral bed flow of the superficial femoral artery in order to provide insight in their hemodynamic relevance. Method A computational model was developed using digital subtraction angiographies in combination with Poiseuille's equation and Ohm's law. Lesions were divided into short and long (Results Stenotic lesions are longer than occlusive lesions ( P Conclusion The maximum collateral system flow of the superficial femoral artery is only a fraction, with a maximum of one fifth, of healthy superficial femoral artery flow. Effects of collateral vessel occlusion during (endo)vascular treatment may therefore be without detrimental consequences.

BACKGROUND AND PURPOSE: Rupture risk of intracranial aneurysms may depend on hemodynamic characteristics. This has been assessed by comparing hemodynamic data of ruptured and unruptured aneurysms. However, aneurysm geometry may change before, during, or just after rupture; this difference causes potential changes in hemodynamics. We assessed changes in hemodynamics in a series of intracranial aneurysms, by using 3D imaging before and after rupture. MATERIALS AND METHODS: For 9 aneurysms in 9 patients, we used MRA, CTA, and 3D rotational angiography before and after rupture to generate geometric models of the aneurysm and perianeurysmal vasculature. Intra-aneurysmal hemodynamics were simulated by using computational fluid dynamics. Two neuroradiologists qualitatively assessed flow complexity, flow stability, inflow concentration, and flow impingement in consensus, by using flow-velocity streamlines and wall shear stress distributions. RESULTS: Hemodynamics changed in 6 of the 9 aneurysms. The median time between imaging before and after rupture was 678 days (range, 14–1461 days) in these 6 cases, compared with 151 days (range, 34–183 days) in the 3 cases with unaltered hemodynamics. Changes were observed for flow complexity ( n = 3), flow stability ( n = 3), inflow concentration ( n = 2), and region of flow impingement ( n = 3). These changes were in all instances associated with aneurysm displacement due to rupture-related hematomas, growth, or newly formed lobulations. CONCLUSIONS: Hemodynamic characteristics of intracranial aneurysms can be altered by geometric changes before, during, or just after rupture. Associations of hemodynamic characteristics with aneurysm rupture obtained from case-control studies comparing ruptured with unruptured aneurysms should therefore be interpreted with caution.

Aim: To investigate the feasibility of using a low-concentration test bolus in abdominal aorta computed tomography (CT) angiography (CTA). Materials and methods: In 10 patients referred for CTA of the abdominal aorta with a body mass index (BMI) ≤28 kg/m2, a standard test bolus of 10 ml contrast medium (CM; 350 mg iodine/ml) was compared with a low-concentration test bolus (5 ml CM; 350 mg iodine/ml; 1:1 diluted with saline) in terms of time to peak enhancement (tPE) and peak enhancement (PE). Results: No significant differences were found between the standard and low-concentration test bolus in terms of tPE and PE. Conclusions A low-concentration test bolus (5 ml, 1:1 diluted with saline) is feasible in patients with a BMI ≤28 kg/m2. Conclusions: A low-concentration test bolus (5 ml, 1:1 diluted with saline) is feasible in patients with a BMI ≤28 kg/m2.

At the Department of Medical Physics at the University of Wisconsin-Madison, research on dual energy chest imaging including the algorithm and patient studies is done using a Pixar image processor computer. In the project described here, a study was made of which low-cost system is able to replace the Pixar and provide high-speed dual energy image processing. The dual energy algorithm was analyzed and the user and system requirements were obtained. A single workstation (e.g. Sun Sparc Station 2) does not provide enough processing power. Therefore accelerator boards for the workstation were reviewed. A prototype system was developed, using an i860-based accelerator board, i.e. the CSPI SuperCard-1, in a Sun 3/150 host computer. Bare computer time for the dual energy algorithm was reduced from 25 min using the Pixar image computer to less than three minutes using the SuperCard-1 processor board. >

In digital diagnostic X-ray imaging the lowpass filtering of the image scene by the system MTF often has to be compensated. Edge enhancement techniques are widely applied, however, in fluoroscopy, where the images are quantum limited, the noise is also enhanced Classical edge enhancement techniques introduce correlated noise structures. These dynamic artefacts deteriorate the conspicuity of fine detail. This contribution describes the work-in-progress about MTF restoration with reduced noise enhancement. As the purpose of this type of image processing is to facilitate the observer tasks in manipulating small catheter tips in a noisy image, the final judgement belongs to this specialized group of experienced observers. The technical comparison, however, has to provide measures such as MTF enhancement, correlation between pixels, signal-to-noise ratios. >

In this paper a highly modular normalized adaptive lattice algorithm for multichannel Least Squares FIR filtering and multivariable system identification, is presented. Multichannel filters with different number of delay elements per input channel are allowed. The main features of the proposed multichannel adaptive lattice least squares algorithm is the use of scalar only operations, multiplications/divisions and square roots, and the local communication which enables the development of a fully pipelinable architecture.

A statistically optimal (in the Cramer-Rao sense) reconstruction of the object wavefunction is presented. The analysis is based on low-dose images of weak phase-amplitude objects obtained by using parallel beams with four specific tilts. The full statistical characterization of the result is given.

In the paper by one of us (H.A.F.) [1], the phase problem was reviewed for circumstances under which the stochastic character of the image could be ignored. A statistical description becomes imperative for images obtained under low-intensity illumination as occurs e.g. in low-dose electron microscopy. Under these circumstances the images are heavily degraded by shot-noise. Often(e.g. [2,3])images are described as a signal plus signal-independent noise. Such a treatment does not apply to shot-noise, the quanta arriving in non-overlapping image cells are statistically independent Poisson-distributed random variables [4]. The variances of the data-counts also contain information about the signal. In this contribution we discuss the retrieval of the object wave function (w.f.) from shot-noise degraded images. Due to the stochastic imaging process, the reconstructed object w.f. is also stochastic. The purpose of this contribution is to establish the statistical characterization of the object w.f. We assume axial coherent quasi-monochromatic illumination. The analysis is presented for one lateral dimension only, the extension to two dimensions is obvious.

The bombardment by electrons of (biological) objects in the electron microscope leads to radiation damage. Accordingly we have to minimize the number of electrons impinging on the object in order to get a reliable image. The image gets a very noisy appearance (shot noise) and the results derived from these images become stochastic quantities of which we would like to obtain the probability distributions. For this program to be carried out we have to know the relation between the image and the object. A schematic of the imaging process is depicted in Fig. 1. The image plane is supposed to be covered by N2 ideal electron counters, where N2 is the number of degrees of freedom (Shannon number) of the image.

The determination of the global extremum of a function is a notorious numerical problem when there are local extrema present. The numerical algorithm which has to determine the global extremum iteratively is in this case very likely to produce a local extremum in the neighborhood of the initial guess of the solution. Moreover, usually one cannot be sure not to have missed an extremum, i.e. various procedures together with various initial values might still overlook the global extremum.

Dit proefschrift handelt over de statistische aspecten van de beeldvorming en de beeldinterpretatie van elektronen-microscoop beelden. Het blijkt dat met name biologische preparaten erg stralingsgevoelig zijn. Om nu stralingsschade aan het object en daarmee artefacten in de afbeelding zoveel mogelijk te beperken, worden de opnamen gemaakt met een zo laag mogelijk aantal elektronen (lage dosis elektronen microscopie). Dit heeft als onmiddellijke consequentie een dominerende aanwezigheid van quantum ruis in de opnamen. De geregistreerde beelden zijn in lage belichtings omstandigheden een realisatie van een stochastisch Poisson proces. ... Zie: Samenvatting

The theory of image formation for an electron microscope is based on the non-relativistic Schrödinger equation, whereas present-day electron microscopes operate with acceleration voltages of the order of one hundred to several hundreds of kilovolts, in which case relativistic effects become important. We present a fully relativistic theory of image formation, based on the appropriate Dirac equation. It is shown that, within certain approximations, always valid for today's electron microscopes, a very simple expression for the current density can still be derived in terms of wave functions that are solutions to the relativistically covariant Klein Gordon equation. The following paper presents the analysis of the often stated possibility to obtain the relativistically correct current density from the non-relativistic current density just by replacing the values of the non-relativistic momentum by the correct relativistic expression.

The fully relativistic quantum mechanical treatment of paraxial electron-optical image formation initiated in the previous paper (this issue) is worked out and leads to a rigorous foundation of the linear transfer theory. Moreover, the status of the relativistic scaling laws for mass and wavelength, as advocated in the literature, is elucidated.