Modern Scanners Research Articles

CO 2 laser stapedotomy with the “one-shot” technique—clinical results

To further optimize the surgical technique with the CO 2 laser in stapes surgery a scanner system was used to obtain a footplate perforation of 0.5 to 0.6 mm with only 1 laser application ("one-shot" stapedotomy). 188 patients with otosclerosis were submitted to a primary CO 2 laser stapedotomy with the SurgiTouch scanner. This study surveys the surgical technique and clinical results. An adequately large perforation diameter could be achieved with a single shot in 68% of the patients treated with the SurgiTouch scanner. In 11% of the patients, a second laser application at the same site was necessary. In 21% of the patients, the perforation had to be enlarged by several slightly overlapping laser applications without scanner. The clinical data of this study clearly documents that there is no evidence of laser depending inner ear affections. The CO 2 laser combined with modern scanner systems is well suited for application in stapes surgery.

Direct sampled I/Q beamforming for compact and very low-cost ultrasound imaging

A wide variety of beamforming approaches are applied in modern ultrasound scanners, ranging from optimal time domain beamforming strategies at one end to rudimentary narrowband schemes at the other. Although significant research has been devoted to improving image quality, usually at the expense of beamformer complexity, we are interested in investigating strategies that sacrifice some image quality in exchange for reduced cost and ease in implementation. This paper describes the direct sampled in-phase/quadrature (DSIQ) beamformer, which is one such low-cost, extremely simple, and compact approach. DSIQ beamforming relies on phase rotation of I/Q data to implement focusing. The I/Q data are generated by directly sampling the received radio frequency (RF) signal, rather than through conventional demodulation. We describe an efficient hardware implementation of the beamformer, which results in significant reductions in beamformer size and cost. We present the results of simulations and experiments that compare the DSIQ beamformer to more conventional approaches, namely, time delay beamforming and traditional complex demodulated I/Q beamforming. Results that show the effect of an error in the direct sampling process, as well as dependence on signal bandwidth and system f number (f#) are also presented. These results indicate that the image quality and robustness of the DSIQ beamformer are adequate for low end scanners. We also describe implementation of the DSIQ beamformer in an inexpensive hand-held ultrasound system being developed in our laboratory.

State-of-the-art ultrasound imaging technology

Ultrasound imaging systems have been used in medicine for over 50 years [1]. Modern scanners have the characteristics of being inexpensive, portable, safe, and real time in nature, all of which make ultrasound one of the most widely used medical imaging modalities. To a great degree, current ultrasound scanners are based on the same fundamental principles as the first devices used for human imaging. Although often referred to as a mature technology, ultrasound imaging continues to evolve in capability, and there seems to be no reason to believe that this evolution will slow in the near future.

Capillaries within compartments: microvascular interpretation of dynamic positron emission tomography data

Measurement of exchange of substances between blood and tissue has been a long-lasting challenge to physiologists, and considerable theoretical and experimental accomplishments were achieved before the development of the positron emission tomography (PET). Today, when modeling data from modern PET scanners, little use is made of earlier microvascular research in the compartmental models, which have become the standard model by which the vast majority of dynamic PET data are analysed. However, modern PET scanners provide data with a sufficient temporal resolution and good counting statistics to allow estimation of parameters in models with more physiological realism. We explore the standard compartmental model and find that incorporation of blood flow leads to paradoxes, such as kinetic rate constants being time-dependent, and tracers being cleared from a capillary faster than they can be supplied by blood flow. The inability of the standard model to incorporate blood flow consequently raises a need for models that include more physiology, and we develop microvascular models which remove the inconsistencies. The microvascular models can be regarded as a revision of the input function. Whereas the standard model uses the organ inlet concentration as the concentration throughout the vascular compartment, we consider models that make use of spatial averaging of the concentrations in the capillary volume, which is what the PET scanner actually registers. The microvascular models are developed for both single- and multi-capillary systems and include effects of non-exchanging vessels. They are suitable for analysing dynamic PET data from any capillary bed using either intravascular or diffusible tracers, in terms of physiological parameters which include regional blood flow.

Estimation of the local statistical noise in positron emission tomography revisited: practical implementation

The purpose of this report is to implement novel modifications to overcome the limitations of an existing algorithm for estimating the local statistical noise in a positron emission tomography (PET) image without performing repeated measures. The original algorithm is based on a modification of the filtered back-projection algorithm that allows the variance to be estimated using only a single sinogram. In addition, the effects of photon absorption, random coincidences, radioactive decay, and detector nonuniformity are taken into account. However, there are some limitations when applying this method with modern scanners. In particular, it is common practice to interleave the projections in the sinogram (to increase the sampling rate along each projection) and to perform an interpolation when actually back-projecting to reconstruct the images. Both of these procedures introduce covariance among the elements of the projections, which is cumbersome and impractical to deal with using the existing technique for creating a variance image. An alternative image reconstruction scheme that is shown to be equivalent to image reconstruction using traditional filtered back-projection greatly simplifies the estimation of the variance image. The proposed methods were tested by Monte Carlo simulations and by using repeated scans of a uniform phantom filled with F-18. Results demonstrate that the proposed methods are very rigorous and stable when compared to calculations of the local variance using either repeated measures with a large number of measurements, or region-of-interest estimates of the variance, assuming homogeneous variance structure. In addition, strategies for extending the proposed technique are discussed that would permit the estimation of the variance due to measurement error of a pixel in a brain map from both single subjects and pooled group data.

OC031: Safety: epidemiology for the practitioner

The practitioner needs to know three things about safety of obstetrical ultrasound: 1. That he or she is responsible for the safe use of medical ultrasound. In 1992 the FDA launched the ODS (output display standards). Manufacturers who want to sell their devices in US, must follow the ODS regulations. This means that safety indices, such as MI (mechanical index) and TI (thermal index) must be displayed on the screen during scanning, if the machines can produce outputs that under theoretical worst-case conditions, may produce biological effects. The responsibility of safe ultrasound scanning was thereby transformed from the manufacturers to the operators of the machine. Thus, the operator needs to know what MI and TI mean, and how to relate to the indices during scanning. 2. That there is limited epidemiological data regarding the safety of obstetrical ultrasound. The available data are from studies with B-mode ultrasound with scanners from the 80's. There are limited data from Doppler studies (color flow or pulsed Doppler), and no data from modern scanners. Modern scanners have much higher outputs than scanners from the 80ies. The epidemiological data are on childhood development (childhood cancer, birthweigth, neurological development, vision, hearing and handedness). There are no data on long term effects (beyond childhood). 3. How to deal with the controversies from epidemiological studies when patients ask. Four epidemiological studies have found a 30% increase in left handedness among males. There are no other epidemiological studies on ultrasound and handedness. However, a statistical significant association between ultrasound scanning during pregnancy and left handedness among males, does not necessarily mean that ultrasound causes the effect. The distinction between a statistical significant association and a causal effect will be discussed. At present, ultrasound should not be denied due to safety considerations from epidemiological studies.

Hardware considerations for functional magnetic resonance imaging

AbstractFunctional magnetic resonance imaging (fMRI) techniques based on changes in blood oxygenation or regional cerebral blood flow or volume have had great impact in mapping the regions of the brain that are activated by specific stimuli. The basic strategy of fMRI paradigms is to acquire data during two different brains states: one state usually comprises a resting condition, while in the other state the subject is performing a specific sensory or cognitive task. The signal difference between the activated and resting signals is on the order of only a few percent, and therefore the reliability and reproducibility with which it can be detected limit both the temporal and spatial resolution of fMRI experiments. The era of fMRI has significantly contributed to advancing the state of the art of MRI scanners. Every hardware component in modern MRI scanners, from the magnet itself to the gradient, shim, and RF coils to peripheral stimulus delivery equipment, has been (re)designed to perform to the limit of currently available technology and to improve the quality of MRI data, particularly fMRI data. The current state of the art of MRI scanners is described in light of their use in fMRI experiments. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson 16A: 35–49, 2003

Radiation dose and dose reduction in multidetector row CT (MDCT)

Since its introduction a few years ago, multidetector row CT (MDCT) has become a widely used diagnostic procedure and has been proven to be a valuable tool for various indications. A major issue using this new modality is the inherent risk of applying increased radiation exposure, when compared to single-slice CT or other imaging modalities.However, MDCT offers some valuable options to save radiation exposure, such as choosing optimized exposure parameters or its superior dose efficiency in comparison to single-slice CT. Multi-phasic examinations should be restricted to indications where definitely necessary. Modern scanners offer intelligent tools for further reduction of radiation dose, such as ECG- or bodyshape-based realtime dose modulation. A new field of applications is the low-dose CT for early detection of diseases. While acquiring thin slices with high spatial resolution, the dose can be reduced to similar values as in conventional radiography, especially when examining under high-contrast conditions. Using all these various options available, radiation exposure can sometimes even be lower than using a conventional single-slice helical CT.

Evaluation of a stereotactic frame for repositioning of the rat brain in serial positron emission tomography imaging studies

For serial imaging studies of the rat brain with positron emission tomography (PET), reproducible positioning of the head can facilitate spatial alignment of images and quantitative analysis. To achieve this aim, we constructed a plastic head frame and tested the positioning reproducibility on a high-resolution small-animal PET scanner, microPET. Two sets of ear bars, with tapers of either 18° (sharp) or 45° (blunt), were evaluated for their relative precision in securing the animal to the frame. For sequential positioning of an animal, average distances from the mean position of 0.51 mm (SD 0.41 mm) and 0.91 mm (SD 0.48 mm) were measured with the sharp and blunt ear bars, respectively. These results show that a rat brain can be reproducibly positioned using the frame, with a variation of position less than the spatial resolution of modern animal PET scanners. Brain regions of interest defined on one scan and copied across subsequent scans of a frame-repositioned animal resulted in an average coefficient of variation of 5.4% (SD 2.7%) using the sharp ear bars and 6.8% (SD 2.5%) using the blunt ear bars. This methodology has the potential to improve quantitative assessment for serial PET studies.

Description and evaluation of the high quality photogrammetric scanner UltraScan 5000

Scanning of analogue images has become a key hardware technology specific to modern digital photogrammetry. Since specialised photogrammetric scanners have been introduced in the late 1980s, a gradual development and improvement of their performance regarding hardware, software and functionality, and productivity has been observed. Originally, geometric accuracy of scanners was the overriding specification for scanners. This is increasingly being augmented by a concern for good colour and radiometric performance. This article describes the UltraScan 5000, a modern photogrammetric scanner manufactured by Vexcel Imaging Austria, and its features, assesses its radiometric and geometric performance with various well-founded tests, and discusses its versatility and use in production. The UltraScan 5000 was introduced in November 1998 and since then, a surprisingly large number of systems has been installed worldwide. Their successful operation illustrates on a daily basis the validity of the technical solution and tests at user sites have confirmed a good to excellent performance regarding geometric accuracy and resolution, radiometric performance (noise, dynamic range) and colour rendition.

HARDWARE CONSIDERATIONS FOR MR IMAGING PHYSICS

Since its commercial introduction as a diagnostic tool in 1984, MR imaging has undergone dramatic improvements in all the features that define image quality. This article discusses what a modern MR imaging scanner should look like and how the components of an MR system, especially the magnet, gradient, and RF components must be matched with one another to ensure optimal performance.

Optimization of a SCALPEL ® exposure tool using a diffractive image quality technique

Determining and maintaining the best exposure parameters, such as dose, focus, or illumination uniformity, is a primary concern in operating a modern day stepper or scanner. A commonly adopted means of obtaining lithographic image quality information relies on accurately measuring CD values across a wafer, die, or image field. Continually shrinking Linewidth have pushed this type of characterization into the realm of the CD-SEM; though greatly improved and automated in recent years, the accuracy required to reliably identify trends makes this a tedious and time consuming practice. We present here an alternative, flexible, and potentially rapid method for optimizing lithography conditions using a diffractive image quality (DIQ) technique, emphasizing its utility in a SCALPEL-based exposure system. A DIQ technique uses the fact that the maximum intensity of higher-order diffraction dispersions is a function of the (image) quality of the grating being illuminated so interrogation of gratings that have been exposed in resist can provide knowledge of how the aerial image quality can be varied for a given set of exposure conditions. We have evaluated grating diffraction efficiency using a probe beam (HeNe laser) introduced at a glancing angle. This arrangement has the advantage of looking at higher order intensity distributions while avoiding the zero order, as well as being fast since one is only collecting signal (eg. No feature recognition searches). Further, it enables the imaging optimization of a new system, such as SCALPEL, without tying up quantitative tools such as a CD-SEM. We have found that this metrology technique provides a quite sensitive and rapid identification of the best exposure conditions. Cross-correlation with a CD-SEM metrology tool has also been performed, in order to verify that the optimum imaging conditions identified through this DIQ technique correspond to the best CD conditions.

Estimating in situ exposure in the presence of acoustic nonlinearity.

Evidence is presented for excess attenuation of pulsed ultrasound due to finite amplitude effects in water. Measurements on a modern scanner are used to demonstrate that linear derating can underestimate many exposure quantities, including all safety indices apart from the cranial thermal index. More appropriate methods for estimating in situ exposure are reviewed. A preferred procedure that requires exposure measurements to be made in water under "small signal" conditions is selected. A spectral index is defined that is proposed as an indicator of finite amplitude effects, where spectral index = 0.1 defines the threshold between nonlinear and quasi-linear conditions.

Application of planar chromatography to sample analysis in the sugar industry

Analysis of sugar mixtures by modern liquid chromatographic techniques, both column and planar, has gained in prominence. As far as planar chromatography is concerned, the introduction of high performance bonded-phase layers and instrumental development techniques has opened up new avenues in the TLC analysis of sugars, especially for samples that normally require cumbersome clean-up processes. In chromatography, gradient elution is the technique of choice when the mixture components span a wide range of polarities (or molecular structure). Planar chromatography gradient development is also possible using an automated technique (AMD), which has been recently introduced. This technique makes large spot capacities possible because of the reconcentration effect caused by the multiple development as well as the accommodation of many spots on the same chromatographic plate, because of the gradient development. Thus, complex samples, such as beet or cane molasses, can be analyzed (or at least screened) on high-performance thin layers using modern scanners which allow a great deal of information to be obtained. In the analysis of molasses, over pressure liquid chromatography (OPLC) is also interesting. This is a forced flow technique which makes both large spot capacities and short development times possible, and can be utilized for gradient elutions as well. Details of the analysis of both beet and cane molasses are reported, and a comparison between the two techniques mentioned previously is discussed.

Advances in three-dimensional diagnostic radiology.

The maturity of current 3D rendering software in combination with recent developments in computer vision techniques enable an exciting range of applications for the visualisation, measurement and interactive manipulation of volumetric data, relevant both for diagnostic imaging and for anatomy. This paper reviews recent work in this area from the Image Sciences Institute at Utrecht University. The processes that yield a useful visual presentation are sequential. After acquisition and before any visualisation, an essential step is to prepare the data properly: this field is known as 'image processing' or 'computer vision' in analogy with the processing in human vision. Examples will be discussed of modern image enhancement and denoising techniques, and the complex process of automatically finding the objects or regions of interest, i.e. segmentation. One of the newer and promising methodologies for image analysis is based on a mathematical analysis of the human (cortical) visual processing: multiscale image analysis. After preprocessing the 3D rendering can be acquired by simulating the 'ray casting' in the computer. New possibilities are presented, such as the integrated visualisation in one image of (accurately registered) datasets of the same patient acquired in different modality scanners. Other examples include colour coding of functional data such as SPECT brain perfusion or functional magnetic resonance (MR) data and even metric data such as skull thickness on the rendered 3D anatomy from MR or computed tomography (CT). Optimal use and perception of 3D visualisation in radiology requires fast display and truly interactive manipulation facilities. Modern and increasingly cheaper workstations ( < $10000) allow this to be a reality. It is now possible to manipulate 3D images of 256 at 15 frames per second interactively, placing virtual reality within reach. The possibilities of modern workstations become increasingly more sophisticated and versatile. Examples presented include the automatic detection of the optimal viewing angle of the neck of aneurysms and the simulation of the design and placement procedure of intra-abdominal aortic stents. Such developments, together with the availability of high-resolution datasets of modern scanners and data such as from the NIH Visible Human project, have a dramatic impact on interactive 3D anatomical atlases.

The acoustic properties of microcalcifications in the context of breast ultrasound

Breast microcalcifications are small crystals of calcium phosphates which are important diagnostic indicators under mammography. Despite continuing advances in the resolution and sensitivity of modern scanners, the role of ultrasound in the breast clinic is limited by the inability of current ultrasound practice to visualize microcalcifications reliably. While mammography is currently the gold standard for their detection, approximately 70% of breast biopsies prompted by the presentation of microcalcifications result in negative biopsy. The improved visualization of microcalcifications under ultrasound could provide additional diagnostic information in these cases, potentially reducing the number of negative biopsies. A review is presented of the theoretical and empirical results to date of this group’s studies of the acoustic properties of microcalcifications as characterized through the application of classical theoretical models, including the Faran model, and through clinical studies of suspected in vivo microcalcifications and breast tissue backscatter. The similarities found between theoretical and clinical results strongly suggest that microcalcifications have elastic scattering properties. The findings are presented in an analysis of the relative impact of phase aberration, spatial resolution, and tissue backscatter on the visualization of microcalcifications with ultrasound. [Work supported by NIH Grant No. RO1-CA43334.]

An evaluation of the reproducibility and responsiveness of four 'state-of-the-art' ultrasonic heel bone measurement systems using phantoms.

This paper evaluates four modern ultrasonic heel bone scanners: the Osteometer DTU-one, Hologic Sahara, CUBA Clinical and Lunar Achilles+. Six phantoms, ranging in porosity from 50% to 83%, were used to evaluate the range of values of broadband ultrasonic attenuation (BUA), speed of sound (SOS) and Stiffness/quantitative ultrasound index (where available) from each machine. Differences in inter-system variability between the lowest and highest porosity phantoms up to a factor of 3.8 were demonstrated. The reproducibility of each system was measured using a single phantom and gave values of 0.03-0.15% for SOS, 0.39-1.6% for BUA and 0.73-1.11% for Stiffness. This contrasted with values of range normalized standard deviation (CX) of 0.2-1.19% for SOS, 0.71-1.86% for BUA and 0.83-1.12% for Stiffness when the output range of the measurement is taken into account. Measures of all quantities differed between machines and care should be taken when expressing and comparing results from different systems.

Image quality of spiral CT versus conventional CT in routine brain imaging

Objective: Aim of the study was to compare image quality of spiral (helical) versus conventional (sequential) routine brain scans obtained on a spiral CT scanner of the latest generation. Materials and methods: In a prospective study 60 patients scheduled for cranial CT were examined in spiral (27 cases) or conventional technique (33 cases) after randomization. Two blinded observers rated artifacts, gray–white-matter contrast and overall image quality. Results: No significant differences in artifacts were detected. Concerning gray–white-matter contrast and overall image quality, none or small differences in favour of conventional scans were found depending on the observer. Conclusion: On a modern scanner image quality of spiral brain scans in adults is nowadays comparable to or only slightly less than that of conventional scans. On such a machine, spiral mode can be recommended if, for example, rapid scanning or high-quality secondary reconstructions are needed.

History of Ultrasonic Duplex Scanning

Ultrasonic duplex scanning was developed and introduced into clinical practice by the combined efforts of engineers and physicians. The instrumentation represents a marriage of B-mode imaging and Doppler technology. Since its introduction in 1974, numerous modifications and upgrading of the technology have taken place. The modern duplex scanner can be used to study vascular disease wherever it is found in the body. Copyright © 1996 Published by Elsevier Science Ltd.

Slip-ring and conventional dynamic hepatic CT: contrast material and timing considerations.

The major conclusions and recommendations of this review of contrast material use are summarized as follows: 1. Our recommendations for routine administration of contrast material are summarized in the Table. 2. Patient factors, such as weight, and liver and cardiovascular disorders may be taken into account when the above recommendations are modified. 3. Unenhanced scanning should be performed selectively. It is unnecessary for routine examinations performed with modern scanners and good contrast material injection techniques. 4. Although conclusive evidence is lacking regarding efficacy, reduced doses of contrast material may be given to patients with an elevated serum creatinine level. A full dose of low-osmolar contrast material may be given to functionally anephric patients if otherwise medically appropriate. 5. Differences in enhancement patterns produced by low-osmolar contrast agents and by high-osmolar contrast agents are small. Choice of contrast material should be based on other factors. 6. The dose of low-osmolar contrast material may be lower than the dose of high-osmolar contrast material so the examination cost may be reduced. 7. Low-osmolar contrast material is not satisfactory to use with delayed iodine scanning. 8. With use of slip-ring scanners and either helical or incremented scanning and recommended techniques, scanning should begin by the end of the injection of contrast material for biphasic techniques and within about 5-15 seconds after the end of injection for monophasic techniques. 9. Section thicknesses no greater than 8 mm should be used for helical or nonhelical scanning. 10. With helical scanning, a 1:1 pitch is preferred with a thickness of 5-8 mm. Overlapping sections may be used selectively to help identify and characterize small lesions. 11. Multiple-pass scanning is helpful to identify hepatocellular carcinoma in cirrhotic livers. This technique may also prove helpful in other conditions. As with any new technology, considerable advantages have come with new challenges, which can be overcome by knowing underlying principles and by attending to detail. Although we have learned much over the past 15 years about proper performance of abdominal CT examinations, we have much yet to learn about the effects of such examinations on the improved health of our patients and on the economic costs to society of providing this form of health care. Opinions on techniques have converged recently, as summarized herein. Therefore, we hope that some centers will now redirect their CT research toward the profoundly difficult, timely, and important issues of examination appropriateness, the value of quality improvement programs, clinical outcomes, and cost-effectiveness.