Acceptance Window Research Articles

Optimal techniques for magnetic resonance imaging of the liver using a respiratory navigator-gated three-dimensional spoiled gradient-recalled echo sequence

PurposeTo optimize the navigator-gating technique for the acquisition of high-quality three-dimensional spoiled gradient-recalled echo (3D SPGR) images of the liver during free breathing. Materials and methodsTen healthy volunteers underwent 3D SPGR magnetic resonance imaging of the liver using a conventional navigator-gated 3D SPGR (cNAV-3D-SPGR) sequence or an enhanced navigator-gated 3D SPGR (eNAV-3D-SPGR) sequence. No exogenous contrast agent was used. A 20-ms wait period was inserted between the 3D SPGR acquisition component and navigator component of the eNAV-3D-SPGR sequence to allow T1 recovery. Visual evaluation and calculation of the signal-to-noise ratio were performed to compare image quality between the imaging techniques. ResultThe eNAV-3D-SPGR sequence provided better noise properties than the cNAV-3D-SPGR sequence visually and quantitatively. Navigator gating with an acceptance window of 2mm effectively inhibited respiratory motion artifacts. The widening of the window to 6mm shortened the acquisition time but increased motion artifacts, resulting in degradation of overall image quality. Neither slice tracking nor incorporation of short breath holding successfully compensated for the widening of the window. ConclusionThe eNAV-3D-SPGR sequence with an acceptance window of 2mm provides high-quality 3D SPGR images of the liver.

FRI0301 A Phase I Pharmacokinetics TRIAL Comparing PF-06438179 (A Potential Biosimilar) and Infliximab in Healthy Volunteers (Reflections B537-01)

BackgroundPF-06438179, a proposed biosimilar to infliximab, has an identical primary amino acid sequence and similar physicochemical, in vitro, and in vivo functional properties to infliximab.ObjectivesThe Phase I study was designed...

A new, behaving, head restrained, eye movement-controlled feline model for chronic visual electrophysiological recordings

BackgroundAnesthetized, paralyzed domestic cats are often used as model organisms in visual neurophysiology. However, in the last few decades, behaving animal models have gathered ground in neurophysiology, due to their advantages over anesthetized, paralyzed models. New MethodIn the present study a new, behaving, awake feline model is described, which is suitable for chronic visual electrophysiological recordings. Two trained, head- fixed cats were suspended in a canvas harness in a specially designed stand. The animals had been trained to fixate the center of a monitor during static and dynamic visual stimulation. Eye movements were monitored with implanted scleral coil in a magnetic field. Cell-level activity was recorded with eight electrodes implanted in the caudate nucleus. ResultsOur two trained cats could maintain accurate fixation, even during optic flow stimulation, in an acceptance window of ±2.5° and ±1.5°, respectively. The model has yielded accurate recordings for over two years. Comparison with Existing Method(s)To our knowledge, this is the first awake, behaving feline model with rigorous eye movement control for chronic, cell-level visual electrophysiological recordings, which has actually proven to work during a longer period. ConclusionsThe new model is optimal for chronic visual electrophysiological recordings in the awake, behaving domestic cat.

Three‐dimensional heart locator for whole‐heart coronary magnetic resonance angiography

Coronary magnetic resonance angiography (MRA) is commonly performed with diaphragmatic navigator (NAV) gating to compensate for respiratory motion, but this approach is inefficient as data must be reacquired when it is outside the acceptance window. We therefore developed and validated a motion compensation technique based on three-dimensional (3D) spatial registration in which data are accepted throughout the respiratory cycle. A novel respiratory motion compensation method was implemented that acquires a low-resolution 3D-image of the heart (3D-LOC) just prior to coronary MRA data acquisition. 3D-LOC volumes were registered to the first 3D-LOC to estimate the respiratory-induced heart motion and to modify the coronary MRA data and reconstruct motion-corrected images. Whole-heart coronary MRA datasets were acquired from nine healthy subjects using a diaphragmatic NAV and using 3D-LOC. There was no significant difference between the subjective image score of NAV and 3D-LOC in three main coronary branches. The vessel sharpness of 3D-LOC was higher than NAV in the right (0.44 ± 0.08 vs. 0.49 ± 0.08; P = 0.055) and left circumflex arteries (0.49 ± 0.05 vs. 0.52 ± 0.04; P = 0.039). Scan time for 3D-LOC was significantly shorter than NAV (4.3 ± 0.6 vs. 8.3 ± 2.3 min; P = 0.004). Compared to NAV gating, 3D-LOC for coronary MRA reduces scan time by nearly 50% without compromising image quality.

Highly efficient 3D motion-compensated abdomen MRI from undersampled golden-RPE acquisitions

A common approach to compensate for respiratory motion in free-breathing 3D magnetic resonance imaging (MRI) is navigator gating where MRI data is only acquired when the respiratory signal coincides within a small predefined acceptance window. However, this leads to poor scan efficiency and prolonged scan times. Here, we propose a method to reconstruct motion-compensated 3D MRI of the abdomen acquired during free-breathing with nearly 100% scan efficiency without increasing scan time. The approach is based on a self-gated golden-radial phase encoding sampling scheme that allows for the reconstruction of multiple undersampled 3D images at different respiratory positions. Non-rigid image registrations and time-wise motion field interpolations are employed to form 3D motion models that combine all low-quality images into one high-quality motion-compensated image. Our highly efficient technique allows reconstruction of 3D liver MRI with a high isotropic resolution of 1.75 mm from a short acquisition of 1.1 min. The approach is validated in 10 healthy volunteers by comparing image quality to data sets acquired with a self-gating approach. Our method reduces scan time by 56% compared to the gating technique while similar image quality is preserved.

Efficient 3D late gadolinium enhancement imaging using the CLAWS respiratory motion control algorithm

Background Acquisition durations of navigator gated high resolution 3D late gadolinium enhancement (LGE) studies are long (1,2). While implementation of the continuously adaptive windowing strategy (CLAWS (3)) - which results in the fastest possible acquisition duration for a given breathing pattern and navigator acceptance window size - may be beneficial, the respiratory-dependent and therefore, nonsmooth k-space acquisition order during gadolinium wash-out could result in increased image artifact. This study was performed to investigate if CLAWS could be used to increase the respiratory efficiency of 3D LGE imaging without detriment to image quality. Methods Whole-heart 3D (32-36 slices, 1.5 x 1.5 x 4 mm, reconstructed to 64-72 slices, 0.7 x 0.7x.2 mm) inversionprepared segmented gradient echo imaging was performed in 18 consecutive patients on a Siemens 1.5 Tesla Avanto scanner. Two acquisitions were performed in random order, one with CLAWS respiratory motion control and one with an end-expiratory tracking accept/reject

Proof of concept for low‐dose molecular breast imaging with a dual‐head CZT gamma camera. Part II. Evaluation in patients

Molecular breast imaging (MBI) has shown promise as an adjunct screening technique to mammography for women with dense breasts. The demonstration of reliable lesion detection with MBI performed at low administered doses of Tc-99 m sestamibi, comparable in effective radiation dose to screening mammography, is essential to adoption of MBI for screening. The concept of performing low-dose MBI with dual-head cadmium zinc telluride (CZT) gamma cameras has been investigated in phantoms in Part I. In this work, the objectives were to evaluate the impact of the count sensitivity improvement methods on image quality in patient MBI exams and to determine if adequate lesion detection could be achieved at reduced doses. Following the implementation of two count sensitivity improvement methods, registered collimation optimized for near-field imaging and energy acceptance window optimized for CZT, MBI exams were performed in the course of clinical care. Clinical image count density (counts/cm(2)) was compared between standard MBI [740 MBq (20 mCi) Tc-99 m sestamibi, standard collimation, standard energy window] and low-dose MBI [296 MBq (8 mCi) Tc-99 m sestamibi, optimized collimation, wide energy window] in a cohort of 50 patients who had both types of MBI exams performed. Lesion detection at low doses was evaluated in a separate cohort of 32 patients, in which low-dose MBI was performed following 296 MBq injection and acquired in dynamic mode, allowing the generation of images acquired for 2.5, 5, 7.5, and 10 min/breast view with proportionately reduced count densities. Diagnostic accuracy at each count density level was compared and kappa statistic was used to assess intrareader agreement between 10 min acquisitions and those at shorter acquisition durations. In patient studies, low-dose MBI performed with 296 MBq Tc-99 m sestamibi and new optimal collimation/wide energy window resulted in an average relative gain in count density of 4.2 ± 1.3 compared to standard MBI performed with 740 MBq. Interpretation of low-dose 296 MBq images with count densities corresponding to acquisitions of 2.5, 5, 7.5, and 10 min/view and median lesion size of 1.4 cm resulted in similar diagnostic accuracy across count densities and substantial to near-perfect intrareader agreement between full 10 min-views and lower count density views. Review of patient studies showed that registered optimized collimation and wide energy window resulted in a substantial gain in count sensitivity as previously indicated by phantom results. This proof of concept work indicates that MBI performed at administered doses of 296 MBq Tc-99 m sestamibi with the applied count sensitivity improvements permits the detection of small breast lesions in patients. Findings suggest that further reductions in acquisition duration or administered dose may be achievable.

Proof of concept for low‐dose molecular breast imaging with a dual‐head CZT gamma camera. Part I. Evaluation in phantoms

Molecular breast imaging (MBI) is a nuclear medicine technology that uses dual-head cadmium zinc telluride (CZT) gamma cameras to image functional uptake of a radiotracer, Tc-99m sestamibi, in the breast. An important factor in adoption of MBI in the screening setting is reduction of the necessary administered dose of Tc-99m sestamibi from the typically used dose of 740 MBq to approximately 148 MBq, such that MBI's whole-body effective dose is comparable to that of screening mammography. Methods that increase MBI count sensitivity may allow a proportional reduction in the necessary administered dose. Our objective was to evaluate the impact of two count sensitivity improvement methods on image quality by evaluating count sensitivity, spatial resolution, and lesion contrast in phantom simulations. Two dual-head CZT-based MBI systems were studied: LumaGem and Discovery NM 750b. Two count sensitivity improvement methods were implemented: registered collimators optimized for dedicated breast imaging and widened energy acceptance window optimized for use with CZT. System sensitivity, spatial resolution, and tumor contrast-to-noise ratio (CNR) were measured comparing standard collimation and energy window setting [126-154 keV (+10%, -10%)] with optimal collimation and a wide energy window [110-154 keV (+10%, -21%)]. Compared to the standard collimator designs and energy windows for these two systems, use of registered optimized collimation and wide energy window increased system sensitivity by a factor of 2.8-3.6. Spatial resolution decreased slightly for both systems with new collimation. At 3 cm from the collimator face, LumaGem's spatial resolution was 4.8 and 5.6 mm with standard and optimized collimation; Discovery NM 750b's spatial resolution was 4.4 and 4.6 mm with standard and optimized collimation, respectively. For both systems, at tumor depths of 1 and 3 cm, use of optimized collimation and wide energy window significantly improved CNR compared to standard settings for tumors 8.0 and 9.2 mm in diameter. At the closer depth of 1 cm, optimized collimation and wide energy window also significantly improved CNR for 5.9 mm tumors on Discovery NM 750b. Registered optimized collimation and wide energy window yield a substantial gain in count sensitivity and measurable gain in CNR, with some loss in spatial resolution compared to the standard collimator designs and energy windows used on these two systems. At low-count densities calculated to represent doses of 148 MBq, this tradeoff results in adequate count density and lesion contrast for detection of lesions ≥8 mm in the middle of a typical breast (3 cm deep) and lesions ≥6 mm close to the collimator (1 cm deep).

Steady state imaging of the thoracic vasculature using inversion recovery FLASH and SSFP with a blood pool contrast agent

Background Although contrast-enhanced first-pass MRA (FP-MRA) is frequently used to visualize the thoracic vasculature, it may not be ideal for the assessment of the aortic root due to poor image quality and motion artifact. Bloodpool contrast agents remain within the intravascular space for several hours, allowing vessels to be imaged longer and therefore improving spatial resolution. The purpose of this study is to compare steady-state magnetic resonance angiography (SS-MRA) following injection of a blood-pool contras agent to first-pass MR angiography (FP-MRA) in adults with thoracic aortic disease. Methods 25 patients (14 men, 11 women) with suspect thoracic aortic disease disease underwent MRA on a 1.5 T scanner (Magnetom Aera and Avanto; Siemens Medical Solutions). The MRA protocol consisted of FP-MRA followed by SS-MRA after intravenous injection of gadofosveset trisodium (Ablavar, Lantheus Medical Imaging). FP-MRA consisted of a breath-held ECG-gated FLASH acquisition in a sagittal oblique orientation with the following imaging parameters: TR/TE: 2.8/1.0, flip angle 25°, FOV 343x500 mm, matrix 264x512, slice thickness 1.5 mm, voxel size 1.3 x 1.0 x 1.0 mm, GRAPPA x 2, 20 second acquisition. 0.03 mmol/kg of gadofosveset was injected intravenously at 1cc/sec in an antecubital vein. Contrast bolus timing was achieved using care bolus technique. SS-MRA consisted of free-breathing ECGgated IR-FLASH and IR-SSFP in a sagittal oblique orientation. IR-FLASH had the following parameters: TR/TE/TI: 3.5/1.5/260, flip angle 18°, and IR-SSFP had: TR/TE/TI: 3.3/1.5/260, flip angle 70°. Both sequences had FOV 326x380, matrix 440x512, slice thickness 1.5 mm, voxel 0.7 x 0.7 x 1.0 mm, GRAPPA x 2, and 3 minute acquisition. Respiratory gating was achieved using a navigator acquisition with an average acceptance window of 35%. For quantitative analysis, orthogonal dimensions of the thoracic aorta were measured at several locations. Signal-to-noise ratio (SNR) was also measured for both techniques by placing regions of interest in the aortic root and the ascending aorta. For qualitative analysis, two independent reviewers evaluated both FP-MRA and SS-MRA images separately. The aortic root and the ascending aorta were scored on an image quality scale of 1-4.

SU‐E‐I‐165: Initial Imaging Results with Manganese‐52 PET Tracer

Purpose: Initial imaging results with the novel positron emission tomography (PET) tracer Mn‐52 in phantoms are reported. This project aims to develop and characterize Mn‐52 as a PET tracer, and to compare results with manganese‐enhanced magnetic resonance imaging (MEMRI). Methods: Mn‐52 was produced by irradiating natural chromium foil (0.5 mm nominal thickness) with protons (12.5 MeV, 2 μA, 60 min). After 10 hours decay, foil was dissolved in aqueous HCl and placed in phantoms for imaging in a Focus 120 microPET scanner. Energy spectra were acquired by varying the scanner photon energy acceptance window. PET images were acquired with and without surrounding non‐radioactive water, with multiple energy windows. A sample of the dissolved foil solution was measured in a gamma‐spectrometer to measure the produced activity. Results: Irradiation produced approximately 6.1 MBq Mn‐52, with 27 kBq Mn‐54. microPET energy spectra feature significantly higher singles count rates at energies above and below the 511 keV positron annihilation peak (compared with F‐18 or Ge‐68) which are attributed to cascade photons from Mn‐52 decay. Phantoms appear clearly in Mn‐52 PET images, with background structure in images attributed to cascade coincidences, amplified by attenuation correction. Background is reduced or eliminated with tighter energy windows (450–600 keV) than are used for standard F‐18 imaging at our centre (350–750 keV). Scanner dead time correction was below 4% with 3.2 MBq Mn‐52 at the centre of the scanner field of view. Conclusions: Mn‐52 is a potentially valuable PET tracer, with some challenges to achieving good quantification. Future work will include testing cascade coincidence correction methods, additional phantom imaging for resolution and image quality, and in vivo imaging studies to characterize and compare with MEMRI.

Use of respiratory biofeedback and CLAWS for increased navigator efficiency for imaging the thoracic aorta

A novel technique to guide a subjects' breathing pattern using a respiratory biofeedback (rBF) "game" to improve respiratory efficiency is presented. The continuously adaptive windowing strategy, a fully automatic and highly efficient free-breathing navigator gated technique, is used to acquire the data as it ensures that all potential navigator acceptance windows are possible. This enables the rBF to be fully adaptable to a subject's respiratory pattern. Images of the thoracic aorta acquired using balanced steady-state free precession with continuously adaptive windowing strategy respiratory motion control, with and without rBF, were compared in 10 healthy subjects. Total scan time was reduced by using rBF. The mean scan time was reduced from 7 min 44 s (463 cardiac cycles, ± 127 cc) without rBF to 5 min 43 s (380 cardiac cycles, ± 118 cc) with the use of rBF (P < 0.05). Respiratory efficiency was increased from 45% without rBF to 56% with rBF (P < 0.01). Image quality was the same for both techniques (P = ns). In conclusion, rBF significantly improved respiratory efficiency and reduced acquisition duration without affecting image quality.

Evaluation of respiratory liver and kidney movements for MRI navigator gating.

To determine the tracking factor by studying the relationship between kidney and diaphragm motions and to compare the efficiency of the gating-and-following and gating-only algorithms in reducing motion artifacts in navigator-gated scans. Diaphragm and kidney motions were measured by using real-time TrueFISP sequences from 10 healthy human volunteers to determine tracking factors at different acceptance windows. Mean tracking factors were used to calculate mean residual errors and improvement factors for the gating-and-following and gating-only algorithms. Mean tracking factors for ± 4, ± 6, ± 8 mm and full acceptance windows ranged from 0.6 to 0.7, with large interindividual variations. Acceptance rates increased as the size of the acceptance window increased (acceptance rate for a 4 mm window ∼50%). There was a greater reduction of motion errors by gating-and-following (maximum of 1.86 mm) than gating-only (maximum of 7.05 mm). Mean tracking factors obtained in this study can be used as a guideline for using the gating-and-following algorithm in navigator-gated kidney scans. The gating-and-following and gating-only algorithms were quantitatively compared, and it was found that the former is more effective in reducing motion errors.

Improving the singles rate method for modeling accidental coincidences in high-resolution PET

Random coincidences (‘randoms’) are one of the main sources of image degradation in PET imaging. In order to correct for this effect, an accurate method to estimate the contribution of random events is necessary. This aspect becomes especially relevant for high-resolution PET scanners where the highest image quality is sought and accurate quantitative analysis is undertaken. One common approach to estimate randoms is the so-called singles rate method (SR) widely used because of its good statistical properties. SR is based on the measurement of the singles rate in each detector element. However, recent studies suggest that SR systematically overestimates the correct random rate. This overestimation can be particularly marked for low energy thresholds, below 250 keV used in some applications and could entail a significant image degradation. In this work, we investigate the performance of SR as a function of the activity, geometry of the source and energy acceptance window used. We also investigate the performance of an alternative method, which we call ‘singles trues’ (ST) that improves SR by properly modeling the presence of true coincidences in the sample. Nevertheless, in any real data acquisition the knowledge of which singles are members of a true coincidence is lost. Therefore, we propose an iterative method, STi, that provides an estimation based on ST but which only requires the knowledge of measurable quantities: prompts and singles. Due to inter-crystal scatter, for wide energy windows ST only partially corrects SR overestimations. While SR deviations are in the range 86–300% (depending on the source geometry), the ST deviations are systematically smaller and contained in the range 4–60%. STi fails to reproduce the ST results, although for not too high activities the deviation with respect to ST is only a few percent. For conventional energy windows, i.e. those without inter-crystal scatter, the ST method corrects the SR overestimations, and deviations from the true random rate are of the order of 1% or less. In addition, in the case of conventional energy window STi results reproduce ST results and therefore the former can be used to obtain the true random rate.

A fully automatic and highly efficient navigator gating technique for high‐resolution free‐breathing acquisitions: Continuously adaptive windowing strategy

A fully automatic and highly efficient free-breathing navigator gated technique, continuously adaptive windowing strategy (CLAWS), is presented. Using a novel and dynamic acquisition strategy that ensures all potential navigator acceptance windows are possible, CLAWS acquires an image with the highest possible efficiency regardless of variations in the respiratory pattern. Unnecessary prolongation of scan durations due to respiratory drift or navigator acceptance window adjustments are avoided. As CLAWS requires no setting of the acceptance window, nor monitoring of the navigator traces during the scan, operator dependence is minimized and ease of use improved. CLAWS was compared against a standard accept/reject algorithm (ARA) and an end-expiratory following ARA (EE-ARA) in 20 healthy subjects and 10 patients (ARA only). The respiratory efficiency was compared against the retrospectively determined best possible respiratory efficiency for each acquisition. On average, the difference between CLAWS scan times and best possible scan times was 0.6% (± 1.3%). For the ARA and EE-ARA techniques, mean differences were 14.4% (± 20.9%) and 32.6 ± 10.9%, respectively. Had the CLAWS algorithm been used with the ARA and EE-ARA traces, mean differences would have been 0.2% (± 1.1%) and 0.5% (± 1.7%), respectively. Image quality was the same for all techniques: respiratory gating, motion artifacts, navigator, and coronary artery imaging.

Experimental evaluation of dual acceptance window weighting function for right coronary MR angiography at 3.0T

To shorten scanning time and increase the feasibility of experimental results, we performed right coronary artery magnetic resonance angiography (CMRA) at 3.0 T using dual acceptance window weighting function in 25 normal subjects. We examined these subjects using conventional navigator with fixed gating window and 6 dual acceptance window weighted gating (DAWG) sequences with different central weighted ratio (CWR). Compared with the conventional navigator sequence, DAWG sequences with CWRs of 20% and 25% increased the scanning efficiency by 30% and 26% respectively (P<.05), while maintaining good image quality; further the corresponding scanning time decreased from 2.12-1.64 and 1.69 min, respectively (P<.05). However, CWRs less than 15% caused image degradation to some extent. The coronary artery lengths and diameters did not show statistically significant differences between the two techniques (P>.05). Briefly, to avoid the problems caused by low navigator efficiency and to maintain comparable image quality, the weighted gating parameters of 3 mm width central acceptance window and 15 mm width outer acceptance window with CWR between 20% and 25% are recommended for right CMRA at 3 T.

Multiplicity fluctuations and correlations in limited momentum space bins in relativistic gases

Multiplicity fluctuations and correlations are calculated within thermalized relativistic ideal quantum gases. These are shown to be sensitive to the choice of statistical ensemble as well as to the choice of acceptance window in momentum space. It is furthermore shown that global conservation laws introduce nontrivial correlations between disconnected regions in momentum space, even in the absence of any dynamics.

Absorption of ϕ mesons in near-threshold proton-nucleus reactions

In the framework of the nuclear-spectral-function approach for incoherent primary proton-nucleon and secondary pion-nucleon production processes, we study the inclusive ϕ-meson production in the interaction of 2.83-GeV protons with nuclei. In particular, the A dependences of the absolute and relative ϕ-meson yields are investigated within the different scenarios for its in-medium width as well as for the cross-section ratio σ pn→pnϕ /σ pp→ppϕ . Our model calculations take into account the acceptance window of the ANKE facility used in a recent experiment performed at COSY. They show that the pion-nucleon production channel contributes distinctly to the ϕ creation in heavy nuclei in the chosen kinematics and, hence, has to be taken into consideration on close examination of the dependences of the ϕ-meson yields on the target mass number with the aim to get information on its width in the medium. They also demonstrate that the experimentally unknown ratio ϕ pn→pnϕ /σ pp→ppϕ has a weak effect on the A dependence of the relative ϕ-meson-production cross section at incident energy of present interest, whereas it is found to be appreciably sensitive to the ϕ in-medium width, which means that this relative observable can indeed be useful to help determine the above width from the direct comparison of the results of our calculations with the future data from the respective ANKE-at-COSY experiment.

Near-threshold ϕ meson production in proton–nucleus reactions and ϕ width in finite nuclei

In the framework of the nuclear spectral function approach for incoherent primary proton–nucleon and secondary pion–nucleon production processes, we study the inclusive ϕ meson production in the interaction of 2.83 GeV protons with nuclei. In particular, the A and momentum dependences of the absolute and relative ϕ meson yields are investigated within the different scenarios for its in-medium width. Our model calculations take into account the acceptance window of the ANKE facility used in a recent experiment performed at COSY. They show that the pion–nucleon production channel contributes distinctly to the ‘low-momentum’ ϕ creation in heavy nuclei in the chosen kinematics and, hence, has to be taken into consideration on close examination of the dependences of the phi meson yields on the target mass number with the aim to get information on its width in the medium. They also demonstrate that both the A-dependence of the relative ϕ meson production cross section and momentum dependence of the absolute ϕ meson yield at incident energy of interest are appreciably sensitive to the phi in-medium width, which means that these observables can be useful to help determine the above width from the direct comparison of the results of our calculations with the future data from the respective ANKE-at-COSY experiment.

Limits on WIMP-nucleon cross-sections from the ZEPLIN-II data

Results are presented from ZEPLIN-II, the world-first 31 kg two-phase xenon dark matter detector. Discrimination between nuclear recoils and background electron recoils is achieved by recording both the scintillation and ionisation signals generated within the liquid xenon, with the ratio of these signals being different for the two classes of events. This ratio is calibrated for different incident species using neutron and γ-ray sources. Background populations of gamma-induced events and radon progeny events were observed in the data. An acceptance window, defined by the neutron calibration data, of 50% nuclear recoil acceptance between 5 keV and 20 keV electron equivalent energy, had an observed count of 29 events, with a summed expectation of 28.6±4.3 γ-ray and radon progeny induced background events. These figures provide a 90% CL upper limit to the number of nuclear recoils of 10.4 events in this acceptance window. This corresponds to a WIMP-nucleon spin-independent cross-section with a minimum of 6.6 × 10-7 pb, and to a WIMP neutron spin-dependent cross-section of 7 × 10-2 pb at a WIMP mass of around 65 GeV.

The hemispherical deflector analyser revisited: II. Electron-optical properties

Using the basic spectrometer trajectory equation for motion in an ideal 1 / r potential derived in Eq. (101) of part I [T.J.M. Zouros, E.P. Benis, J. Electron Spectrosc. Relat. Phenom. 125 (2002) 221], the operational characteristics of a hemispherical deflector analyser (HDA) such as dispersion, energy resolution, energy calibration, input lens magnification and energy acceptance window are investigated from first principles. These characteristics are studied as a function of the entry point R 0 and the nominal value of the potential V ( R 0 ) at entry. Electron-optics simulations and actual laboratory measurements are compared to our theoretical results for an ideal biased paracentric HDA using a four-element zoom lens and a two-dimensional position sensitive detector (2D-PSD). These results should be of particular interest to users of modern HDAs utilizing a PSD.