Acquisition Of High-quality Images Research Articles

Use of Bedside Ultrasonography for Endotracheal Tube Placement in Pediatric Patients: A Feasibility Study

The purpose of our study was to evaluate the usefulness of bedside ultrasonography in verifying endotracheal tube placement in the pediatric population. This study consisted of 2 phases. In phase I, subjects were examined while intubated and after extubation to determine the presence of the endotracheal tube by applying each of 2 ultrasound transducers to the cricothyroid membrane. In phase II, pediatric patients were examined in the emergency department during intubation or immediately after intubation to ascertain proper endotracheal tube placement by using bedside ultrasonography. These results were compared with the results obtained with a colorimetric end-tidal carbon dioxide detector and chest radiographs. Forty-nine and 50 patients (age: 1 day to 17 years) were recruited in the first and second phases of the study, respectively. The endotracheal tube was detected in all 99 patients by using bedside ultrasonography. Two views were required to show accurately the presence of the endotracheal tube in the trachea. Visualization was obtained in all cases, although short necks and cervical collars made the procedure more challenging. The sniffing position allowed for the best acquisition of high-quality images. Our linear transducer provided the best images but, because of its size, it was not ideal when space was limited. Therefore, the curvilinear transducer was used exclusively for phase II. During phase II, the mean times to acquire bedside ultrasonographic images of the endotracheal tube through the cricothyroid membrane and to obtain a chest radiograph were 17.1 seconds and 14.0 minutes, respectively. In 3 cases, bedside ultrasonographic images proved to be invaluable when the colorimetric end-tidal carbon dioxide detector yielded false-negative or equivocal readings. Bedside ultrasonography can be used to accurately and rapidly determine the presence of the endotracheal tube within the trachea in pediatric patients.

IDEAL Imaging of the Musculoskeletal System: Robust Water–Fat Separation for Uniform Fat Suppression, Marrow Evaluation, and Cartilage Imaging

The objective of this article is to discuss the acquisition of high-quality MR images of the musculoskeletal system with uniform fat suppression using iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL). IDEAL is a three-point water-fat separation method that provides robust fat suppression even in the complex magnetic environments commonly encountered during clinical musculoskeletal imaging. The IDEAL technique provides uniform fat saturation even in complex magnetic environments and simultaneously produces in-phase and opposed-phase images that may be useful for characterization of osseous lesions. The IDEAL water-fat separation method is highly versatile and has been successfully combined with T1-weighted, T2-weighted, steady-state free precession, and spoiled gradient-recalled echo techniques to produce high-quality MR images in clinically acceptable scanning times.

Optimization of fast spiral chemical shift imaging using least squares reconstruction: Application for hyperpolarized 13C metabolic imaging

A least-squares-based optimization and reconstruction algorithm has been developed for rapid metabolic imaging in the context of hyperpolarized (13)C. The algorithm uses a priori knowledge of resonance frequencies, J-coupling constants, and T(2)* values to enable acquisition of high-quality metabolic images with imaging times of approximately 100 ms for an 8-cm field of view (FOV) and 0.5 cm isotropic resolution. A root-mean-square error (rMSE) analysis is introduced to optimize metabolic image quality by appropriate choice of pulse sequence parameters, echo times, and signal model. By performing the reconstruction in k-space, the algorithm also allows the inclusion of the effect of chemical shift evolution during the readout period. Single-interleaf multiecho spiral chemical shift imaging (spCSI) is analyzed in detail as an illustrative example for the use of the new reconstruction and optimization algorithm. Simulation of the in vivo spectrum following the bolus injection of hyperpolarized (13)C(1) pyruvate shows that single-interleaf spiral spectroscopic imaging can achieve image quality in 100 ms, comparable to the performance of a 13-s phase-encoded chemical shift imaging (FIDCSI) experiment. Single-interleaf spCSI was also tested at a 3-T MR scanner using a phantom containing approximately 0.5-M solutions of alanine, lactate, and a pyruvate-pyruvate hydrate C(1)-C(2) ester at thermal equilibrium polarization, all enriched to 99% (13)C in the C(1) carbonyl positions. Upon reconstruction using the k-space-based least-squares technique, metabolite ratios obtained using the spCSI method were comparable to those obtained using a reference FIDCSI acquisition.

MRI of Moving Subjects Using Multislice Snapshot Images With Volume Reconstruction (SVR): Application to Fetal, Neonatal, and Adult Brain Studies

Motion degrades magnetic resonance (MR) images and prevents acquisition of self-consistent and high-quality volume images. A novel methodology, Snapshot magnetic resonance imaging (MRI) with Volume Reconstruction (SVR) has been developed for imaging moving subjects at high resolution and high signal-to-noise ratio (SNR). The method combines registered 2-D slices from sequential dynamic single-shot scans. The SVR approach requires that the anatomy in question is not changing shape or size and is moving at a rate that allows snapshot images to be acquired. After imaging the target volume repeatedly to guarantee sufficient sampling every where, a robust slice-to-volume registration method has been implemented that achieves alignment of each slice within 0.3 mm in the examples tested. Multilevel scattered interpolation has been used to obtain high-fidelity reconstruction with root-mean-square (rms) error that is less than the noise level in the images. The SVR method has been performed successfully for brain studies on subjects that cannot stay still, and in some cases were moving substantially during scanning. For example, awake neonates, deliberately moved adults and, especially, on fetuses, for which no conventional high-resolution 3-D method is currently available. Fine structure of the in-utero fetal brain is clearly revealed for the first time and substantial SNR improvement is realized by having many individually acquired slices contribute to each voxel in the reconstructed image.

Synchrotron-based intravenous cerebral angiography in a small animal model

K-edge digital subtraction angiography (KEDSA), a recently developed synchrotron-based technique, utilizes monochromatic radiation and allows acquisition of high-quality angiography images after intravenous administration of contrast agent. We tested KEDSA for its suitability for intravenous cerebral angiography in an animal model. Adult male New Zealand rabbits were subjected to either angiography with conventional x-ray equipment or synchrotron-based intravenous KEDSA, using an iodine-based contrast agent. Angiography with conventional x-ray equipment after intra-arterial administration of contrast agent demonstrated the major intracranial vessels but no smaller branches. KEDSA was able to visualize the major intracranial vessels as well as smaller branches in both radiography mode (planar images) and tomography mode. Visualization was achieved with as little as 0.5 ml kg−1 of iodinated contrast material. We were able to obtain excellent visualization of the cerebral vasculature in an animal model using intravenous injection of contrast material, using synchrotron-based KEDSA.

Practical Aspects of Assessing Tumors Using Clinical Diffusion-weighted Imaging in the Body

Diffusion-weighted magnetic resonance (MR) imaging (DWI) is increasingly applied to evaluate tumors in the abdomen and pelvis. However, DWI is susceptible to a variety of artifacts that arise from motion, use of strong gradient pulses, and echo-planar imaging technique. We discuss practical issues to help radiologists optimize the use of DWI to evaluate tumors in the body, including breath-hold DWI, multiple-acquisition non-breath-hold DWI, and diffusion-weighted whole-body imaging with background body signal suppression (DWIBS). Considerations of meticulous technique, sequence optimization, and quality assurance are emphasized for consistent acquisition of high quality images. We illustrate the potential use of these techniques to detect and characterize tumors and to monitor treatment effects.

Assessment of left ventricular asynchrony using volume—time curves of 16 segments by real‐time 3 dimensional echocardiography: Comparison with tissue Doppler imaging

Recent technical developments with high-resolution real-time 3 dimensional echocardiography (RT3DE) facilitate the acquisition of high quality images and the analysis of segmental volume-time curves (VTCs). To assess left ventricular (LV) asynchrony using the VTCs of 16 segments by RT3DE, and to evaluate accuracy compared to tissue Doppler imaging (TDI). Twenty-three heart failure (HF) patients (LVEF: 25+/-6%, age: 60+/-13 years) and 16 normal controls underwent TDI and RT3DE. The standard deviation (SD3) of the end systolic time reaching minimal systolic volume for the 16 segments on VTCs was obtained by RT3DE. The standard deviation (SD2) of the electromechanical coupling time for the 8 segments was measured using TDI. SD3 was markedly higher in HF patients than in controls (7.7+/-2.5 vs 1.5+/-1.0%, P<0.01) and increased as LVEF decreased (r=-0.85, P<0.01). SD2 was also significantly higher in HF patients (27.0+/-8.6 vs 12.6+/-5.0 ms, P<0.01) and had a good negative correlation with LVEF (r=-0.72, P<0.01). SD3 was well correlated to SD2 (r=0.66, P<0.01). We suggest that analysis of VTCs in 16 segments using RT3DE may be a useful alternative to TDI for the evaluation of LV asynchrony.

Daily organ tracking in intensity-modulated radiotherapy of prostate cancer using an electronic portal imaging device with a dose saving acquisition mode

Background and purposeDaily use of conventional electronic portal imaging devices (EPID) for organ tracking is limited due to the relatively high dose required for high quality image acquisition. We studied the use of a novel dose saving acquisition mode (RadMode) allowing to take images with one monitor unit per image in prostate cancer patients undergoing intensity-modulated radiotherapy (IMRT) and tracking of implanted fiducial gold markers. Patients and methodsTwenty five patients underwent implantation of three fiducial gold markers prior to the planning CT. Before each treatment of a course of 37 fractions, orthogonal localization images from the antero-posterior and from the lateral direction were acquired. Portal images of both the setup procedure and the five IMRT treatment beams were analyzed. ResultsOn average, four localization images were needed for a correct patient setup, resulting in four monitor units extra dose per fraction. The mean extra dose delivered to the patient was thereby increased by 1.2%. The procedure was precise enough to reduce the mean displacements prior to treatment to ≤0.3mm. ConclusionsThe use of a new dose saving acquisition mode enables to perform daily EPID-based prostate tracking with a cumulative extra dose of below 1Gy. This concept is efficiently used in IMRT-treated patients, where separation of setup beams from treatment beams is mandatory.

Image-guided radiotherapy using a mobile kilovoltage x-ray device

A mobile isocentric C-arm kilovoltage imager has been evaluated as a potential tool for image-guided radiotherapy. The C-arm is equipped with an amorphous silicon flat panel for high-quality image acquisition. Additionally, the device is capable of cone beam computed tomography (CT) and volumetric reconstruction. This is achieved through the application of a modified Feldkamp algorithm with acquisition over a 180 degrees scan arc. The number of projections can be varied from 100 to 1000, resulting in a reconstructed volume 20 cm in diameter by 15-cm long. While acquisition time depends upon number of projections, acceptable quality images can be obtained in less than 60 seconds. Image resolution and contrast of cone-beam phantom images have been compared with images from a conventional CT scanner. The system has a spatial resolution of > or = 10 lp/cm and resolution is approximately equal in all 3 dimensions. Conversely, subject contrast is poorer than conventional CT, compromised by the increased scatter and underlying noise inherent in cone beam reconstruction, as well as the absence of filtering prior to reconstruction. The mobility of the C-arm makes it necessary to determine the C-arm position relative to the linear accelerator isocenter. Two solutions have been investigated: (1) the use of fiducial markers, embedded in the linac couch, that can subsequently be registered in the image sets; and (2), a navigation approach for infrared tracking of the C-arm relative to the linac isocenter. Observed accuracy in phantom positioning ranged from 1.0 to 1.5 mm using the navigation approach and 1.5 to 2.5 mm using the fiducial-based approach. As part of this work, the impact of respiratory motion on cone-beam image quality was evaluated, and a scheme for retrospective gating was devised. Results demonstrated that kilovoltage cone beam CT provides spatial integrity and resolution comparable to conventional CT. Cone-beam CT studies of patients undergoing radiotherapy have demonstrated acceptable soft tissue contrast, allowing assessment of daily changes in target anatomy. Of the 2 approaches developed to register images to the linac isocenter, the navigation method demonstrated superior accuracy for daily patient positioning relative to the fiducial-based method. Finally, significant image degradation due to respiratory motion was observed. It was demonstrated that this could be improved by correlating the acquisition of individual 2D projections with respiration for retrospective reconstruction of phase-based volumetric datasets.

Assessment of Left Ventricular Function by Analysis of Volume-Time Curves of 16 Segments with Real-Time Three Dimensional Echocardiography : Left Ventricular Asynchrony as a Clinical Parameter for Patients with Heart Failure

Background and Objectives：Recent technical developments with high-resolution real-time 3-dimensional echocardiography (RT3DE) have facilitated the acquisition of high quality images and the analysis of segmental volumetime curves (VTCs). The purposes of this study were to assess left ventricular (LV) asynchrony with using the VTCs of 16 segments by RT3DE and to compare this with tissue Doppler imaging (TDI) as a clinical parameter. Subjects and Methods：Twenty-three heart failure (HF) patients (LVEF: 25±6%, age: 60±13 years) and 16 normal controls underwent TDI and RT3DE at baseline and 1-year. The standard deviation (SD3) of the end systolic time to reach the minimal systolic volume for the 16 segments on VTCs was obtained by RT3DE. The standard deviation (SD2) of the electromechanical coupling time for the 8 segments was measured using TDI. Results： SD3 was markedly higher in the HF patients than that in the controls (7.7±2.5 vs 1.5±1.0%, respectively, p< 0.01) and it increased as the LVEF decreased (r=-0.85, p<0.01). SD2 was also significantly higher in the HF patients (27.0±8.6 vs 12.6±5.0 msec, respectively, p<0.01) and it had good negative correlation with the LVEF (r=-0.72, p<0.01). SD3 was well correlated with SD2 (r=0.66, p<0.01). At 1-year, the HF patients with an increased LVEF showed a decreased SD3 (7/13). In contrast, the patients with a decreased LVEF had an increased SD3 (3/13). Conclusion：The analysis of VTCs for the 16 LV segments with using RT3DE from a single acoustic window may be a useful clinical parameter for evaluating the LV function, including LV asynchrony, the LV volume and the LVEF. (Korean Circulation J 2006;36:669-675)

Machine Vision Based on Optical Properties of Biomaterials for Fruit Grading System

It is known that biomaterials have unique characteristics in their color, shape, size, spectral reflectance, and biological structure which are different from industrial materials. Specific machine vision designs are often required for constructing inspection, monitoring, measuring, or production systems to handle the biomaterials. In this presentation, cuticular layers on fruit surfaces are in focus and a direct lighting device with a polarizing filter, which was developed for a fruit inspection system is introduced, because illumination is one of the most important components. Since the biomaterials have various reflectance in different wavelength bands, characteristics of light from gamma ray to terahertz were described. In the visible region, there are many types of light sources, which have different properties on luminance, lumen maintenance, color rendering, color temperature, life, and cost. A high quality image acquisition requires a proper light source selection. Fruit grading facilities are places where the largest number of machine vision systems are practically used in agricultural fields. In this paper, a conventional fruit grading machine and a fruit grading robot with machine visions are introduced. In addition, a contribution of the imaging technologies of the grading systems to the food traceability system is explained.

Image acquisition with immersion objective lenses using electrons emitted with several tenths of an electron volt energies: Towards high spatial resolution ESCA analysis

This study aims to evaluate the spatial resolution achievable with photoelectrons in order to perform localised UPS or XPS analyses on various heterogeneous samples. This investigation is intentionally restricted to direct image acquisition by immersion objective lenses, involving electrons ejected with initial energies of several tenths of an electron-volt. In order to characterise the contribution of all optical elements, analytical investigations were associated to numerical simulations based on SIMION 7 software. The acquisition of high-quality images implies a simultaneous reduction in spherical and chromatic aberrations by a narrow aperture stop placed at the output pupil of the objective. With such limitations in useful emission angles, it is shown that monochromatic electron beams build images with a resolution of about 1 nm, especially for the acceleration bias mode where the focussing electrode is biased at a positive high voltage. Even energy dispersed electron beams, limited by a 4 eV band pass spectrometer, can produce images convenient for highly localised ESCA analyses (resolution 3 nm), where the objective lens is associated with an aperture stop of 30 μm in diameter without using acceleration voltages above 5000 V.

The potential for neurovascular intravenous angiography using K-edge digital subtraction angiography

Background: Catheterization of small-caliber blood vessels in the central nervous system can be extremely challenging. Alternatively, intravenous (i.v.) administration of contrast agent is minimally invasive and therefore carries a much lower risk for the patient. With conventional X-ray equipment, volumes of contrast agent that could be safely administered to the patient do not allow acquisition of high-quality images after i.v. injection, because the contrast bolus is extremely diluted by passage through the heart. However, synchrotron-based digital K-edge subtraction angiography does allow acquisition of high-quality images after i.v. administration of relatively small doses of contrast agent. Materials and methods: Eight adult male New Zealand rabbits were used for our experiments. Animals were submitted to both angiography with conventional X-ray equipment and synchrotron-based digital subtraction angiography. Results: With conventional X-ray equipment, no contrast was seen in either cerebral or spinal blood vessels after i.v. injection of iodinated contrast agent. However, using K-edge digital subtraction angiography, as little as 1 ml iodinated contrast agent, when administered as i.v. bolus, yielded images of small-caliber blood vessels in the central nervous system (both brain and spinal cord). Conclusions: If it would be possible to image blood vessels of the same diameter in the central nervous system of human patients, the synchrotron-based technique could yield high-quality images at a significantly lower risk for the patient than conventional X-ray imaging. Images could be acquired where catheterization of feeding blood vessels has proven impossible.

Computer-aided Image Acquisition and Colorimetric Analysis of Paintings

In the context of archiving of fine art paintings, we have developed various techniques for the computer-aided digital acquisition, processing and analysis of high-quality and high-definition color images. After a short review of existing systems, we present our approach to this problem. After a general set-up and calibration, a digital image of the painting is captured using an electronic camera. The image is then corrected for inhomogeneities of the illumination, misalignment of the three color channels and poor colorimetric quality due to the camera's non-colorimetric spectral sensitivities. The corrected digital image is thus quantified accurately by device-independent color components and can be analyzed colorimetrically, visualized faithfully on a calibrated display, reproduced on a high-quality printer and/or archived for further use. In the final part of this article, we demonstrate the use of such images for a colorimetric analysis of three oil paintings from different epochs.

Implementation and utility of a daily ultrasound-based localization system with intensity-modulated radiotherapy for prostate cancer

Purpose : To evaluate the clinical feasibility of daily computer-assisted transabdominal ultrasonography for target position verification in the setting of intensity-modulated radiotherapy (IMRT) for prostate cancer. Methods and Materials : Twenty-three patients with clinically localized prostate cancer were treated using a sequential tomotherapy IMRT technique (Peacock) and daily computer-assisted transabdominal ultrasonography (BAT) for target localization. Patients were instructed to maintain a full bladder and were placed in the supine position using triangulation tattoos and a leg immobilizer to minimize pelvic rotation. The BAT ultrasound system is docked to the treatment collimator and electronically imports the CT simulation target contours and isocenter. The system is able to use the machine isocenter as a reference point to overlay the corresponding CT contours onto the ultrasound images captured in the transverse and sagittal planes. A touch screen menu is used to maneuver the CT contours in three dimensions such that they match the ultrasound images. The system then displays the three-dimensional couch shifts required to produce field alignment. Data were prospectively collected to measure the frequency by which useful ultrasound images were obtained, the amount of time required for localization/setup, and the direction/magnitude of the positional adjustments. Results : Of the 23 patients, the BAT ultrasound system produced images of sufficient quality to perform the overlay of the CT contours in 19 patients such that positional verification could be reliably performed. Poor image quality was associated with patient inability to maintain a full bladder, large body habitus, or other anatomic constraints. Of the 19 assessable patients, a total of 185 treatment alignments were performed (mean 8.8/patient). For all cases, the average time required for the daily ultrasound imaging and positional adjustments was 11.9 min. After the initial 5 cases, the user experience skills improved such that the time required for image verification/positional adjustments decreased to a mean of 5.6 min. The average right-left, AP, and cranial-caudal adjustment was 2.6 ± 2.1 mm, 4.7 ± 2.7 mm, and 4.2 ± 2.8 mm, respectively. Positional adjustments >10 mm were infrequent and related primarily to misidentification of the target structures on the ultrasound image, patient movement, or improper registration of the triangulation tattoos. Conclusion : Daily computer-assisted BAT ultrasound positional verification of the prostate can be successfully performed through the acquisition of high-quality images in most patients with only a modest increase in treatment setup time. Positional data obtained with this system resulted in clinically meaningful adjustments in daily setup for sequential IMRT that would not be otherwise apparent from other verification modalities.

Clinical role of 99mTcO4/MIBI scan, ultrasound and intra-operative gamma probe in the performance of unilateral and minimally invasive surgery in primary hyperparathyroidism

The main purposes of this study were: (a) to investigate the efficacy of an imaging protocol based on the combination of (99m)TcO4/MIBI scintigraphy and neck ultrasound (US) in selecting patients with primary hyperparathyroidism (HPT) for unilateral neck exploration, and (b) to help define the role of the intraoperative MIBI gamma probe (IMGP) technique in the performance of minimally invasive radio-guided surgery (MIRS). One hundred and forty-three consecutive patients with primary HPT were enrolled in the study. We used a modified (99m)TcO4/MIBI scintigraphic procedure which included the oral administration of potassium perchlorate to cause rapid (99m)TcO4 washout from the thyroid tissue, thereby permitting the acquisition of high-quality early MIBI images. A single-photon emission tomography (SPET) acquisition was also obtained in 21 patients, of whom seven had an enlarged parathyroid gland (EPG) in the mediastinum at planar scintigraphy and 14 had discordant scan/US findings for the presence of a cervical EPG. Neck US was performed in the same session as scintigraphy using a small-parts, high-resolution 10-MHz transducer. All patients were then operated on by the same surgical team. Quick PTH assay (QPTH) was used to measure PTH intraoperatively to confirm successful parathyroidectomy. In patients with scan/US evidence of a solitary EPG and with a normal thyroid gland, limited, unilateral neck surgery or, more recently, MIRS was planned (n=91). In patients with scan/US evidence of multiglandular disease (MGD) (n=21) or concomitant nodular goitre (n=24) or in patients with a negative scan/US evaluation (n=7), extensive bilateral neck exploration was planned (n=52). In 87 of the 91 patients (95.6%) in whom preoperative imaging indicated the presence of a solitary EPG and a normal thyroid gland, a single parathyroid adenoma was found at surgery, and these patients were treated by unilateral neck exploration or MIRS. In the remaining four patients of this group, conversion to bilateral neck exploration was required because parathyroid carcinoma (n=3) or MGD (n=1) was diagnosed at operation. In some cases SPET was helpful in better localising the EPG. In particular, in 5 of the 21 patients evaluated, SPET localised an EPG deep in the neck or mediastinum and at surgery a parathyroid adenoma was found in the paratracheal or para-oesophageal space. In 43 of the 46 patients (93.5%) who were candidates for MIRS, the IMGP technique allowed parathyroidectomy to be performed through a small, 2- to 2.5-cm skin incision with a short duration of intervention (mean 34min). We conclude that: (a) The integrated scan/US imaging protocol that we used appears to be accurate in selecting patients with primary HPT for unilateral neck exploration. (b) In our series the most prevalent cause of bilateral neck exploration was the co-existence of a nodular goitre; thus accurate preoperative evaluation of the thyroid gland by dual-tracer scintigraphy and US imaging is strongly recommended in all patients with HPT. (c) SPET can provide the surgeon with useful information when an EPG is located deep in the neck or mediastinum. (d) IMGP appears to be a useful intraoperative device in HPT patients with solitary parathyroid adenomas and a normal thyroid gland, since it permits minimally invasive and time-saving surgery.

Guidelines for the cardiac sonographer in the performance of contrast echocardiography: Recommendations of the American Society of Echocardiography Council on Cardiac Sonography

J Am Soc Echocardiogr 2001;14:417-20.

High resolution MRI of the brainstem at 8 T.

A recently developed ultra high field MRI system operating at 8 T (UHFMRI) was applied for brainstem imaging. UHFMRI was performed in five healthy volunteers (three men, two women; age range 34--46 years). Sagittal and axial slices were obtained with the following settings: GE, TR 750--1,000 ms, TE 7-9 ms, FOV 20 cm, matrix 1,024 x 1,024 or 512 x 512 points, slice thickness 2 mm, resolution 195 or 390 microm/pixel. The brainstem structures were assigned based on anatomy and course. Images with good signal strength and homogeneity were acquired from the midbrain and the pons. Main intraaxial structures could be directly visualized. The periaqueductal gray matter and nuclei had higher signal intensity than the predominantly white matter structures such as the corticobulbar/corticopontine/corticospinal tracts, the sensory lemnisci, and the medial longitudinal fasciculus. Structures with high iron content such as the substantia nigra and the red nucleus were seen as prominent signal hypointensities. Numerous vessels traversing the brainstem including small perforators were also distinguished. It is concluded that UHFMRI enables the acquisition of high quality images of the upper brainstem with details approaching that of histologic specimen.

Measurement of endometrial thickness at US in multicenter drug trials: value of central quality assurance reading.

To assess the value of central quality assurance (QA) reading of transvaginal ultrasonographic (US) images obtained to measure endometrial thickness and to assess image quality. Results of 2,000 US examinations performed in 1,000 subjects during one of two multicenter drug trials were evaluated. Endometrial thickness was measured at the study site; images were then sent to the QA center, where an experienced sonologist evaluated endometrial thickness and image quality. In 360 (18%) of the 2,000 examinations, image quality was insufficient for central QA reading. Repeat examinations were requested, and suggestions for improvement in technique were provided. In 349 (97%) of the 360 examinations, repeat US images were of acceptable quality. In 99 (5%) of the 1,989 examinations in which endometrial thickness was measured, central measurement of thickness differed by more than 2 mm from that of the site. In a group (n = 300) that was followed up for 1 year, requests for repeat US examinations decreased from 24% at baseline to 11% at 1 year. Central QA reading provides a consistent evaluation of endometrial thickness on US images obtained in multicenter drug trials and helps to ensure the acquisition of high-quality transvaginal US images. It further leads to demonstrable improvement in site performance.

General principles of endoscopic ultrasonographic imaging

Endoscopic ultrasonography (EUS) uses high-frequency acoustic waves within the gastrointestinal lumen to obtain detailed images of the gut wall and surrounding structures. Knowledge of basic ultrasound (US) physics is important for both acquisition of high-quality images and accurate interpretation. US waves are produced by transducers, which also act as receivers for reflected waves, or echoes. Images are formed by processing of the electrical signals resulting from reception of echoes by the transducer. Tiny pulses of US energy are emitted into tissue along a single plane by either a mechanically rotated transducer or a fixed array of transducers. A structure's depth is determined by the time it takes for the US pulse to return to the transducer. The intensity of a returning echo depends on the reflectivity of the target structure and the amount of energy loss, or attenuation, in tissue. Real time imaging is possible because of rapid renewal of images several times per second. Axial (or depth) resolution is determined by US pulse length; it is optimal at high US frequencies. However, tissue penetration decreases as frequency is increased, limiting the depth of imaging. Lateral resolution is a function of the width of each US wave or beam. Transducer size and frequency determine the shape and dimensions of the beam, which typically converges at a distance of 2 to 3 cm from the transducer and diverges thereafter. Lateral resolution is best in the narrowest portion, termed the focal zone . In general, optimal resolution occurs with use of the highest possible frequency that allows adequate penetration to the structures of interest. Two types of echoes are produced in tissue: scattering of US waves by tiny particles or irregular surfaces, and reflection at interfaces between layers of tissue with different acoustic properties. EUS imaging of the gut wall is used to illustrate several of the fundamental US principles detailed in this article. An overview of the basic types of EUS instruments and certain applications, such as Doppler or duplex scanning, is also provided.