Optimal Imaging Conditions Research Articles

Measurements of T1- and T2-relaxation Time Changes According to the Morphological Characteristics of Gold Nanoparticles (GNPs)

Purpose : The aim of this study is to measure the typical MR variables such as - and -relaxation times according to morphological characteristics of gold nanopartides as a preliminary study to perform theragnosis using local heating by gold nanopartides. Materials and Methods : Two types of gold nanoparticles were used. Spheres were synthesized by various methods and stirring speed. Rods were synthesized by adding various concentrations of sphere nanopartides. Gold nanopartides were mixed with 2% agarose gel at 1:1 ratio and then signals were acquired using a 1.5T MRI. For the measurements of -and -relaxation times, TR and TE were varied, respectively. The results were acquired through and curves based on the intensities of MR image using self-developed software. And Statistical analysis was performed. Results : times were measured 1.86 sec and 2.08 sec for sphere and rod, respectively. On the other hands, times were measured 57 ms and 35.45 ms for sphere and rod. Conclusion : The changes of the MR variables according to the morphological characteristics of the gold nanopartides were confirmed. Optimal MR imaging conditions can be obtained by choosing proper TR and TE according to the type of nanoparticles.

High-speed atomic force microscopy for large scan sizes using small cantilevers

We present a high-speed atomic force microscope that exhibits a number of practical advantages overprevious designs. Its central component is a high-speed scanner with a maximum scan size of 23 µm × 23 µm and a conveniently largesample stage area (6.5 mm × 6.5 mm). In combination with small cantilevers, image rates of up to 46 images s − 1 in air and 13 images s − 1 in liquid arereached under z-feedback control. By large scan size imaging of collagen fibrils in air, sample velocities of 8.8 mm s − 1 in thexy-directionand 11 mm s − 1 in the z-direction are reached. To provide optimized imaging conditions for both largeand small scan sizes, a modular scanner design allows easily exchanging thex- andy-piezos. The scanner is therefore also suited for investigations on the molecular andatomic scale, which is demonstrated by imaging the step dynamics of a calcitesurface during dissolution and the hexagonal lattice of a mica surface in liquid.

Estimation of tumor microvessel density by MRI using a blood pool contrast agent

Recognition of importance of angiogenesis to tumor growth, metastasis, and treatment outcome has led to efforts to develop non-invasive methods for longitudinal monitoring of tumor microvasculature. We describe a steady-state MRI technique to determine absolute blood volume (BV) as a marker of microvascular density with improved spatial and temporal resolution using an ultra small super paramagnetic iron oxide (USPIO). A noise reduction scheme for BV imaging was also proposed based on weighting factors derived by pre-contrast signal level as an adjustable additive constant. Gradient echo sequence was used for BV imaging with MRI at 7T. Optimal imaging conditions (USPIO dose and echo time) were determined by USPIO dose-dependent studies ex vivo and in vivo. Improved analysis strategies were at first applied for cerebral BV estimation in mice, which were found in good agreement with the literature values. These methods were then used to determine tumor BV in mice. The optimal concentration of USPIO for BV estimates was found to range from 3.6 to 4.48 mM (estimated as Fe concentration) in ex vivo experiments corresponding to an in vivo dosage of 215-287 micromol/kg body weight, whereas a USPIO dose of 287 micromol/kg leads to higher cerebral BV estimate in vivo than the reported values. Application of the BV imaging method to evaluation of anti-angiogenic effect of Sunitinib in squamous cell carcinoma (SCC) tumor bearing mice revealed approximately 46% reduction in tumor BV 4 days after start of Sunitinib treatment. The results show that the MRI approach using USPIO yields high-resolution absolute BV images and the method can be conveniently applied to monitor longitudinal tumor microvessel density changes as a function of growth or in response to treatment.

Evaluation of imaging plates as recording medium for images of negatively stained single particles and electron diffraction patterns of two-dimensional crystals

We evaluated imaging plates (IPs) and the DITABIS Micron scanner for their use in recording images of negatively stained single-particle specimens and electron diffraction patterns of two-dimensional crystals. We first established the optimal imaging and read-out conditions for images of negatively stained single-particle specimens using the signal-to-noise ratio of the images as the evaluation criterion. We found that images were best recorded on IPs at a magnification of 67,000x, read out with a gain setting of 20,000 and a laser power setting of 30% with subsequent binning over 2 x 2 pixels. Our results show that for images of negatively stained specimens, for which the resolution is limited to approximately 20 A, IPs are a good alternative to EM film. We also compared IPs with a 2K x 2K Gatan charge-coupled device (CCD) camera for their use in recording electron diffraction patterns of sugar-embedded two-dimensional crystals. Diffraction patterns of aquaporin-0 recorded on IPs and with the CCD camera showed reflections beyond 3 A and had similar R(Friedel) as well as R(merge) values. IPs can thus be used to collect diffraction patterns, but CCD cameras are more convenient and remain the best option for recording electron diffraction patterns.

Simultaneous topography and recognition imaging: physical aspects and optimal imagingconditions

Simultaneous topography and recognition imaging (TREC) allows for the investigation ofreceptor distributions on natural biological surfaces under physiological conditions.Based on atomic force microscopy (AFM) in combination with a cantilever tipcarrying a ligand molecule, it enables us to sense topography and recognition ofreceptor molecules simultaneously with nanometre accuracy. In this study weintroduce optimized handling conditions and investigate the physical properties of thecantilever–tip–sample ensemble, which is essential for the interpretation of theexperimental data gained from this technique. In contrast to conventional AFMmethods, TREC is based on a more sophisticated feedback loop, which enablesus to discriminate topographical contributions from recognition events in theAFM cantilever motion. The features of this feedback loop were investigatedthrough a detailed analysis of the topography and recognition data obtained on amodel protein system. Single avidin molecules immobilized on a mica substratewere imaged with an AFM tip functionalized with a biotinylated IgG. A simpleprocedure for adjusting the optimal amplitude for TREC imaging is describedby exploiting the sharp localization of the TREC signal within a small range ofoscillation amplitudes. This procedure can also be used for proving the specificity ofthe detected receptor–ligand interactions. For understanding and eliminatingtopographical crosstalk in the recognition images we developed a simple theoretical model,which nicely explains its origin and its dependence on the excitation frequency.

Aberration-corrected ADF-STEM depth sectioning and prospects for reliable 3D imaging in S/TEM

The short depth of focus of aberration-corrected scanning transmission electron microscopes (STEMs) could potentially enable 3D reconstruction of nanomaterials through acquisition of a through-focal series. However, the contrast transfer function of annular dark-field (ADF)-STEM depth sectioning has a missing-cone problem similar to that of tilt-series tomography. The elongation as a function of the probe-forming angle is found to be (square root of 3/2) x 1/alphamax. For existing aberration-corrected STEMs operated at optimal imaging conditions, the elongation factor for depth sectioning is larger than 30. This large elongation factor results in highly distorted shapes of 3D objects and unexpected artifacts due to the loss of information. Depth-sectioning experiments using a 33-mrad 100 keV C(5)-corrected aberration-corrected STEM demonstrate the elongation effect and the missing-cone problem in real and reciprocal space. The performance limits of different S/TEM-based imaging modes are compared. There is a missing cone of information for bright-field S/TEM, ADF-STEM, hollow-cone ADF-STEM and coherent scanning confocal electron microscopy (SCEM). Only incoherent SCEM fills the missing cone.

Real-time phase-contrast imaging at the Kurchatov synchrotron radiation source

Experiments on the real-time in-line phase imaging of biological objects at the second generation synchrotron radiation source are reported. High intensity “pink” beam was obtained using the reduced electron beam energy of the accelerator. Optimal conditions for phase-contrast imaging at the low coherence source are discussed.

Analytic derivation of optimal imaging conditions for incoherent imaging in aberration-corrected electron microscopes

The optimal lens parameters for incoherent imaging using third and fifth-order aberration-corrected electron microscopes are derived analytically. We propose simple models for the point spread function (PSF) and transfer function that give analytic formulae for the lateral resolution and depth resolution. We also derive an analytic formula for the contrast transfer function (CTF) in three dimensions and show that depth sectioning has an information limit equivalent to tomography with a missing cone of 90 ∘ minus the aperture angle.

Anaesthesia for interventional neuroradiology

Anaesthesia is required for neuroradiological diagnostic procedures such as angiograms, computerized tomography (CT), and magnetic resonance imaging (MRI) or for therapeutic intervention (Table 1). Interventional neurovascular procedures are part of a trend towards minimally invasive neurosurgery, an important development in which has been the introduction of the Guglielmi detachable coil (GDC) for endovascular aneurysm coiling. Evidence that coiling is associated with a better outcome than craniotomy and clipping is moving more procedures out of theatres into the neuroradiology suite. Prolonged procedures, improved patient safety, and optimal conditions for imaging have resulted in a trend towards a greater use of general anaesthesia (GA), especially in aneurysm and arteriovenous malformation (AVM) treatments, while conscious sedation is preferred for cerebral ischaemic disease (carotid stents, angioplasty, and thrombolysis). Though many of the risks encountered in this newer arena are conceptually similar to traditional neurosurgery, important differences in the working environment and practice exist.

Adaptive 4D MR imaging using navigator‐based respiratory signal for MRI‐guided therapy

For real-time 3D visualization of respiratory organ motion for MRI-guided therapy, a new adaptive 4D MR imaging method based on navigator echo and multiple gating windows was developed. This method was designed to acquire a time series of volumetric 3D images of a cyclically moving organ, enabling therapy to be guided by synchronizing the 4D image with the actual organ motion in real time. The proposed method was implemented in an open-configuration 0.5T clinical MR scanner. To evaluate the feasibility and determine optimal imaging conditions, studies were conducted with a phantom, volunteers, and a patient. In the phantom study the root mean square (RMS) position error in the 4D image of the cyclically moving phantom was 1.9 mm and the imaging time was approximately 10 min when the 4D image had six frames. In the patient study, 4D images were successfully acquired under clinical conditions and a liver tumor was discriminated in the series of frames. The image quality was affected by the relations among the encoding direction, the slice orientation, and the direction of motion of the target organ. In conclusion, this study has shown that the proposed method is feasible and capable of providing a real-time dynamic 3D atlas for surgical navigation with sufficient accuracy and image quality.

Performance evaluation of a table-top Compton camera for various detector parameters

A prototype table-top Compton camera, composed of two small plane-type position-sensitive semiconductor detectors, is under development. The objective of this study was to find the optimal imaging conditions for the Compton camera in order to maximize its performance in terms of imaging resolution and imaging sensitivity. To that end, the performance of the Compton camera was simulated varying several detector parameters (i.e., the photon energy of the source, the geometrical configuration of the component detectors, and the interaction position resolution of the absorber detector), using the GEANT4 detector simulation toolkit. The Compton camera was found to show its highest performance for the photon energy of 364.5 keV ( 131I), but also showed a relatively high performance for 511 keV ( 18F) and 662 keV ( 137Cs). The Compton camera showed its highest performance also when the scatterer and absorber detectors were positioned in parallel, separated by 10 cm. Finally, it was found significantly beneficial to the imaging resolution to increase the interaction position resolution of the absorber detector to 0.3×0.3 cm 2 in the planar direction and to 0.5 cm in the axial direction.

Effect of a physical phase plate on contrast transfer in an aberration-corrected transmission electron microscope

In this theoretical study we analyze contrast transfer of weak-phase objects in a transmission electron microscope, which is equipped with an aberration corrector ( C s-corrector) in the imaging lens system and a physical phase plate in the back focal plane of the objective lens. For a phase shift of π/2 between scattered and unscattered electrons induced by a physical phase plate, the sine-type phase contrast transfer function is converted into a cosine-type function. Optimal imaging conditions could theoretically be achieved if the phase shifts caused by the objective lens defocus and lens aberrations would be equal to zero. In reality this situation is difficult to realize because of residual aberrations and varying, non-zero local defocus values, which in general result from an uneven sample surface topography. We explore the conditions—i.e. range of C s-values and defocus—for most favourable contrast transfer as a function of the information limit, which is only limited by the effect of partial coherence of the electron wave in C s-corrected transmission electron microscopes. Under high-resolution operation conditions we find that a physical phase plate improves strongly low- and medium-resolution object contrast, while improving tolerance to defocus and C s-variations, compared to a microscope without a phase plate.

Achieving sub-1.6-nm resolutions of a low-voltage microscopic focused-ion-beam system not involving aberration correction

The final, second, part is presented of an investigation into possible methods of achieving the ultimate resolution for focused-ion-beam (FIB) microscopes. Our strategy differs from the well-known FIB technologies in the following respects: (i) It employs an advanced ion source of effective radius ≈1 nm. (ii) The ion energy at the target is as low as −300 eV. (iii) Potential secondary emission of ions and electrons is used as a means of imaging at the nanometer scale. The version in part 1 relies on a chromatic-aberration correction system based on a combined electromagnetic mirror. As an alternative, we here propose reducing the ion-optical system to a scale of tens of micrometers. It is shown by computer simulation that the resolution thus obtained should be as good as the one reported in part 1 (∼1.6 nm). Under optimal imaging conditions, the ion-beam current on a target is found to depend only on the properties of the ion source and to be the same as those of macroscopic FIB systems regardless of their operating voltage.

Optimisation of acquisition parameters for radiography using numerical simulation

X-ray imaging is a powerful tool for the inspection of industrial castings. The radiograph quality is highly dependent of a large number of inspection parameters: generator settings, object geometrical parameters and detector characteristics. When trying to optimise these parameters, the large dimensionality of the problem makes manual investigation of the solution difficult. Within European project VERDICT, we propose to use simulation to predict the optimal imaging conditions, and thus to help the operator to tune the system prior to the inspection. We use a simulation software tool called 'Sindbad'. For every particular set of acquisition parameters, a corresponding radiograph is simulated. A main loop scans the whole parameters space to find the optimal parameters set, using a defect detectability criteria as cost function. Detector response is precisely modelled, both for film and flat panel. Different versions of the detectability criteria are discussed, depending on whether detection is performed by numerical processing or human inspection. Experimental validation of our approach is performed using components from aeronautics.

Investigation of fluid cell resonances in intermittent contact mode atomic force microscopy

In fluid, the probe resonance curve of the atomic force microscope contains several apparent resonance peaks whose origin is not well understood. In this work, the authors focus on identifying the cause of these peaks and finding the optimal imaging conditions for acoustic intermittent contact mode in fluid environment. The authors demonstrate that the peaks are also present in the spectrum of the fluid movement and in that of the shaker piezo. These peaks may or may not coincide with the natural resonance of a probe in liquid, thus it is possible to drive the probes off-resonance. Numerical calculations show the feasibility of off-resonance imaging, but predict much higher imaging force.

DYNAMIC COMPUTED TOMOGRAPHY OF THE PANCREAS IN NORMAL DOGS AND IN A DOG WITH PANCREATIC INSULINOMA

To establish optimal imaging conditions for enhanced computed tomography (CT) for canine pancreatic tumors, 10 healthy beagles were subjected to dynamic CT. This technique was then applied to a dog with suspected insulinoma. The changes in mean peak enhancement and the delay time of the aorta and pancreas were determined. In normal beagles, maximal arterial and pancreatic CT enhancement was observed at 15 +/- 2 s (795 +/- 52 Housfield unit [HU]) and 28 +/- 9 s (118 +/- 16HU) after contrast medium injection, respectively. Multiphase enhanced CT was performed in a pug with suspected insulinoma using the CT protocol defined for the normal beagles with some parameters modified; the images were acquired at the arterial (14 s after contrast medium injection), pancreatic (after 28 s), and equilibrium (after 90 s) phases; scanning was followed by exploratory laparotomy. CT images were characterized by an enhanced mass in the left pancreatic lobe at the arterial phase, during which the difference between the CT values of the mass and normal pancreas was the highest. Histopathologic diagnosis of the pancreatic mass was insulinoma. Thus, it appears that enhanced CT imaging can be used to delineate the pancreas from a pancreatic mass, and it may be helpful in deciding the need for surgery.

Diffraction imaging and diffuse scattering by small dislocation loops

Defining the limits of visibility of small defect clusters and dislocation loops, and optimal diffraction conditions for electron microscope imaging remains one of the central problems of electron microscopy of irradiated materials. Using computer image simulations based on the propagation–interpolation algorithm for solving the Howie–Basinski equations, we investigate the relation between the actual and the ‘observed’ size of small loops, the part played by many-beam dynamical diffraction effects, and limitations of electron microscope imaging in identifying the structure of small defects. We also discuss the link between real-space imaging and diffuse scattering by small dislocation loops.

MAC mode atomic force microscopy studies of living samples, ranging from cells to fresh tissue

Magnetic AC mode (MAC mode) atomic force microscopy (AFM), a novel type of tapping mode AFM in which the cantilever is driven directly by a magnetic field, is a powerful tool for imaging with high spatial resolution and better signal-to-noise in liquid environment. It may largely extend the application of AFM to living samples, especially those are sensitive to cantilever forces, even to multilayer tissue samples. However, there are few reports on the imaging of living cells by MAC mode AFM previously. In our present study, we explore the optimal imaging conditions of MAC mode AFM on living astrocytes and fresh arterial intima surface. We also used nude tips for PicoTREC panel (i.e., Aux in BNC, a new data collecting channel) to image living samples and discussed its difference with phase imaging. We show that living biological samples can be imaged by MAC mode AFM at details of comparable resolution as those by high resolution scanning electron microscopy. Furthermore, the combination of height, amplitude, phase and TREC panel signals provide abundant informations for the characteristics of living samples, such as topography, profile, stiffness and adhesion.

Compositional contrast in Al xGa 1− xN/GaN heterostructures using scanning spreading resistance microscopy

Scanning spreading resistance microscopy has found extensive use as a dopant-profiling technique for silicon-based devices, and to a lesser extent for some III–V materials. Here we demonstrate its efficacy for wide bandgap nitrides and, in particular, show that it may be used to differentiate between layers of different Al-content in an Al x Ga 1− x N/GaN heterostructure. A monotonic increase in resistance signal with increasing Al-content is demonstrated, under optimal imaging conditions. The variation in measured resistance with applied bias is shown to be dependent on the aluminium content, and this is discussed, along with other issues, in the context of potential quantification of unknown samples. The procedure for forming an optimal image is different from that for silicon, in terms of contact forces and applied biases.

SU‐FF‐I‐85: Optimization of Image Quality and Minimization of Radiation Dose for Chest Computed Radiography

Purpose: To investigate the effects of x‐ray exposure parameters and added beam filtration on patient dose and image quality for optimization of chest computed radiography (CR). Method and Materials: A chest x‐ray phantom (CardinalHealth Model 76‐211) was used to simulate a patient of standard size. To achieve a small or a large patient size, one sheet of 25‐mm acrylic was removed or added, respectively. Pre‐ and post‐patient x‐ray spectra were measured using a CdTe x‐ray spectrometer at various exposure conditions and added filters. kVp stations of 80, 100, and 120 were selected. An Al plate of 0, 1.0, 2.0, 3.0 mm or a Cu plate of 0, 0.1, 0.3, 0.5 mm was placed at the tube exit window for each exposure setting. Patient entrance exposure was measured using a Radcal ion chamber under automatic exposure control at each exposure condition. Corresponding CR images were acquired at above conditions using a contrast‐detail phantom (CDRAD) placed between acrylic plates of the chest phantom for evaluating image quality. The same protocol for processing of CR image plate was used throughout. Both printed films and digital images were archived. Reading sessions were conducted to interpret the 72 CR images. Results: CDRAD images were ranked based on image quality. Corresponding patient dose and x‐ray spectrum were analyzed. Beam effective energy and spectrum information were evaluated. Optimal imaging condition was determined. In general, with increased beam filtration and effective energy, image quality decreased with dose saving as expected. However, at certain conditions of patient size, filtration, and kVp, image quality actually appeared improved with reduced or comparable patient dose. Conclusion: Proper use of pre‐patient filtration can improve CR chest image quality while maintaining or reducing patient dose at carefully selected kVp setting for a patient. Optional filters should be made available for digital chest radiography.