Development of small adenocarcinoma phantoms for comparison of image quality among various chest X-ray systems

The aim of our study was to develop a phantom of lung adenocarcinoma for use in a comparative evaluation of image quality among various chest X-ray systems. In this study, we developed type A, B, and C phantoms of lung adenocarcinoma according to Noguchi's classification. The shape of lung adenocarcinoma was assumed to be spherical with a different density in the core. The shapes of the phantoms were obtained by calculating equivalent thickness to X-ray transmission, leading to the same shadow as the sphere in order to perform practical visual evaluation using a chest lung phantom to which the phantoms were attached. The phantoms were tough water phantoms made by Kyoto Kagaku Co., Ltd. The performance of the phantoms was validated for chest radiographs of the phantoms attached to the surface of the chest lung phantom. The results of visual evaluation of tumor detectability by 13 radiologists and technicians showed generally good agreement with previous clinical data.     

Three-dimensional hindfoot alignment measurements based on biplanar radiographs: comparison with standard radiographic measurements

Objective

To establish a hindfoot alignment measurement technique based on low-dose biplanar radiographs and compare with hindfoot alignment measurements on long axial view radiographs, which is the current reference standard.

Materials and methods

Long axial view radiographs and low-dose biplanar radiographs of a phantom consisting of a human foot skeleton embedded in acrylic glass (phantom A) and a plastic model of a human foot in three different hindfoot positions (phantoms B1–B3) were imaged in different foot positions (20° internal to 20° external rotation). Two independent readers measured hindfoot alignment on long axial view radiographs and performed 3D hindfoot alignment measurements based on biplanar radiographs on two different occasions. Time for three-dimensional (3D) measurements was determined. Intraclass correlation coefficients (ICC) were calculated.

Results

Hindfoot alignment measurements on long axial view radiographs were characterized by a large positional variation, with a range of 14°/13° valgus to 22°/27° varus (reader 1/2 for phantom A), whereas the range of 3D hindfoot alignment measurements was 7.3°/6.0° to 9.0°/10.5° varus (reader 1/2 for phantom A), with a mean and standard deviation of 8.1°?±?0.6/8.7°?±?1.4 respectively. Interobserver agreement was high (ICC?=?0.926 for phantom A, and ICC?=?0.886 for phantoms B1–B3), and agreement between different readouts was high (ICC?=?0.895–0.995 for reader 1, and ICC?=?0.987–0.994 for reader 2) for 3D measurements. Mean duration of 3D measurements was 84?±?15/113?±?15 s for reader 1/2.

Conclusion

Three-dimensional hindfoot alignment measurements based on biplanar radiographs were independent of foot positioning during image acquisition and reader independent. In this phantom study, the 3D measurements were substantially more precise than the standard radiographic measurements.     

Area beam equalization: optimization and performance of an automated prototype system for chest radiography

RATIONALE AND OBJECTIVES: To evaluate the feasibility and performance of an x-ray beam equalization system for chest radiography using anthropomorphic phantoms. MATERIALS AND METHODS: Area beam equalization involves the process of the initial unequalized image acquisition, attenuator thickness calculation, mask generation using a 16 x 16 piston array, and final equalized image acquisition. Chest radiographs of three different anthropomorphic phantoms were acquired with no beam equalization and equalization levels of 4.8, 11.3, and 21. Six radiologists evaluated the images by scoring them from 1-5 using 13 different criteria. The dose was calculated using the known attenuator material thickness and the mAs of the x-ray tube. RESULTS: The visibility of anatomic structures in the under-penetrated regions of the chest radiographs was shown to be significantly (P < .01) improved after beam equalization. An equalization level of 4.8 provided most of the improvements with moderate increases in patient dose and tube loading. Higher levels of beam equalization did not show much improvement in the visibility of anatomic structures in the under-penetrated regions. CONCLUSION: A moderate level of x-ray beam equalization in chest radiography is superior to both conventional radiographs and radiographs with high levels of beam equalization. X-ray beam equalization can significantly improve the visibility of anatomic structures in the under-penetrated regions while maintaining good image quality in the lung region.     

Computer-simulated lung nodules in digital chest radiographs for detection studies

Computer simulations of lung nodules overcome many shortcomings of creating radiographs using anthropomorphic nodule phantoms for lung nodule detection studies, but these algorithms can be cumbersome and involved. A simple, fast, and flexible computer program to simulate lung nodules in digital chest radiographs for detection studies is reported. To verify the realism of the simulated nodules, a psychophysical study and a statistical study were conducted. In the psychophysical study, six radiologists and four nonradiologists were asked to distinguish between 17 real lung nodules and 17 computer-simulated lung nodules shown in eight radiographs. The results show that the computer-simulated lung nodules are indistinguishable visually from real lung nodules. Using parameters from the Rose model of vision, results show that the simulated and real nodules are the same statistically. Thus, besides visual validity, statistical analysis in confirming the validity of the simulated lung nodules is included.     

Anthropomorphic carotid bifurcation phantom for MRI applications.

Anthropomorphic carotid bifurcation flow phantoms that incorporate different stenotic geometries within the internal carotid artery have been developed. This technique produces high-fidelity, life-size vascular flow models that are compatible with magnetic resonance techniques. The models, in conjunction with a computer-controlled flow pump, address the need for a complex vascular geometry that can be used to verify magnetic resonance angiography (MRA) techniques that quantify stenosis severity and blood flow. Stenotic geometries, with up to 80% diameter reduction, have been fabricated in two different phantom materials. Plastic phantoms provide a durable, rigid geometry where the absolute dimensions of the model are well known. Agar gel phantoms provide tissue-like signal (T1, T2) up to the lumen boundary and are also compatible with ultrasound techniques. In this paper the technique to produce vascular flow phantoms is outlined and the compatibility of these phantoms with MRA techniques is demonstrated. J. Magn. Reson. Imaging 1999;10:533-544.     

Improved pulmonary nodule detection with scanning equalization radiography

The potential for improved pulmonary nodule detection with scanning equalization radiography (SER) was evaluated by means of observer performance testing during the interpretation of posteroanterior conventional radiographs and SER images of an anthropomorphic chest phantom with simulated nodules. A test set of 200 conventional and 200 SER radiographs of phantoms containing either one nodule or none was interpreted by four radiologists attempting to detect a nodule and indicate a confidence value. Their ability to detect nodules positioned over the lung was slightly improved with SER compared with conventional radiography (sensitivity, .56 vs .70); for nodules over the mediastinum or diaphragmatic areas, it was much improved (sensitivity, .29 vs .64). The results were also analyzed with receiver-operating characteristic methods, which revealed a significant improvement in lesion detect-ability over the thicker body parts with SER images. The capability of equalized chest radiographs to provide improved lesion detectability suggests that SER may set a new standard for film-based chest radiography and have a large clinical application.     

A validation of computational phantoms from photographic images for patient-tailored whole body counting

This study attempted to validate a new method for patient-tailored efficiency calibration. Digital calibration with Monte Carlo simulations was used to substitute the lack of precision limitation due to the limited number of experimental phantoms in whole body counting calibration for internal dosimetry. The validity of this approach was examined by comparing the simulation results to the measured values from actual measurements using family BOMAB phantoms. The computational voxel phantoms were constructed by a reconstruction technique using AP and lateral photographic images of the BOMAB phantoms, instead of using the given specifications provided with BOMAB phantoms. Although discrepancies to a certain degree between the computational simulation and measured efficiencies do exist, the results support the new approach of being an alternative to family BOMAB phantoms.     

Quantitative optical coherence tomographic elastography: method for assessing arterial mechanical properties

Optical coherence tomography elastography represents a potentially attractive new technique for measuring elastic properties of tissues on a micron scale. In this study, the feasibility of optical coherence tomography (OCT) to study the mechanical properties of phantoms and atherosclerotic arterial samples is reported. The elastic modulus of tissue-mimicking phantoms was measured using OCT and correlated with mechanical measurements. The results indicate that elastography based on OCT represents an attractive technique for evaluating the mechanical properties of tissues.     

Evaluation of mammographic image quality: pilot study comparing five methods.

A radiograph is considered of high quality when it allows a radiologist to identify abnormalities with high sensitivity and specificity. Although many methods for assessing image quality have been devised, it is not clear which is most meaningful or how well these methods correlate with one another. A pilot study was undertaken to compare five methods of evaluating mammographic image quality. Each of the methods was used to form separate rankings of 11 mammographic system configurations. In two of the methods, observers (three radiologists and three physicists) subjectively ranked the "image quality" of radiographs of phantoms obtained with each configuration. The third method ranked the systems according to contrast as measured densitometrically with an aluminum step wedge, and the fourth, in terms of lowest to highest mean glandular radiation doses to the breast. In the final method, observers based their rankings on mammograms of patients. The intra- and interobserver variabilities of each ranking method were assessed, as well as the correlations between methods, by using standard nonparametric statistical tests. Intraobserver consistency was high with any of the image quality ranking methods; however, image quality rankings based on either of the two phantoms provided better agreement among observers than did rankings based on images of patients. Surprisingly, no significant degree of correlation was found between any two image quality evaluation methods. Our work may have two implications for the American College of Radiology Mammography Accreditation Program: (1) small variations in phantom scores do not necessarily correlate with subjective variation in image quality in radiographs of patients, and (2) when small numbers of radiographs are used, the assessment of the quality of mammograms of patients may vary considerably among radiologists.     

Multiple-beam equalization radiography in chest radiology. Image quality and radiation dose considerations

The large difference in transmission between the mediastinum and the part of the chest mainly containing lungs causes major problems in chest radiography. A system for advanced multiple beam equalization radiography has been evaluated. Evaluation of image quality has been performed both using standard phantoms and from clinical radiographs. Measurements of radiation dose burden to the patient have been made both in clinical examinations and using an anthropomorphic phantom. The image quality, in areas with low transmission, is substantially increased using the equalization system. In parts of the chest mainly containing lung tissue, conventional systems show an equal or slightly better image quality. The radiation dose burden to the patient is increased by 25 percent using the equalization system, as compared to a low-dose air-gap system. In our opinion, the slight increase in radiation dose burden is well motivated by the high overall quality of the radiographs produced.     

Image quality of mammographic systems

The image quality in mammography was evaluated for all the 56 equipment-image receptor combinations used in Finland with two phantoms containing test objects of three types and different sizes. We obtained 2-8 fold variations for the smallest sizes of the three objects (specks, fibres and masses) visible in the X-ray images and 3.0-3.7 fold variations for an "image score". The smallest speck, fibre and mass sizes visible in the radiographs were 0.24, 0.75 and 0.5 mm, respectively. An unacceptable image quality was obtained in 36% of the studied cases. A recommendation is presented.     

Stereolithographic models simulating trabecular bone and their characterization by thin-slice- and micro-CT

The analysis of bone structure in vivo is an important goal in osteoporosis, because the determination of bone mineral density alone is insufficient to predict whether an individual patient will eventually suffer an osteoporotic fracture or not. An additional structural analysis may significantly improve the statistical assessment of fracture risk. In this study we present a method to generate realistic although enlarged 3D phantoms of trabecular bone. These phantoms are useful in characterizing the potential of in vivo imaging procedures for the analysis of bone structure and to verify textural or structural analysis methods applied to these images. Our phantoms are based on a real trabecular bone specimen that was converted to a plastic model using the technique of stereolithography. The trabecular network is modeled by hydroxyapatite. Limitations of the stereolithographic process prevent the generation of exact 1:1 replicas of the real bone. A histomorphometric analysis of microCT scans of the phantoms showed that an excellent replication of the bone structure could be achieved in phantoms enlarged by a factor of 2.5 with "trabecular" hydroxyapatite concentrations up to 400 mg/cm3. In order to demonstrate the usefulness of our phantoms, we investigated one of them with various thin-slice CT protocols using clinical single- and multi-slice spiral CT scanners. The enlargement of the phantoms limits their use on high spatial resolution CT scanners (resolution >20 lp/cm). The limited hydroxyapatite concentration requires enhanced exposure rates for the phantoms scans to offset the larger impact of noise due to the lower contrast in the phantoms.     

Evaluation of the usefulness of color digital summation radiography in temporally sequential digital radiographs: a phantom study

Purpose The purpose of this study was to assess the usefulness of color digital summation radiography (CDSR) for detection of nodules on chest radiographs by observers with different levels of experience. Materials and methods A total of 30 radiographs of chest phantoms with abnormalities and 30 normal ones were arranged at random. Set A was conventional radiographs only. Set B consisted of both conventional radiographs and CDSR images, which were colored with magenta. Five chest radiologists and five residents evaluated both image sets on a TFT monitor. The observers were asked to rate each image set using a continuous rating scale. The reading time for each set was also recorded. Results In set A, the performance of chest radiologists was significantly superior to that of the residents (P < 0.05). However, in set B, there was no significant difference in the performance of the chest radiologists and the residents. In both observer groups, the mean reading time per case in set B was significantly shorter than that in set A (P < 0.01). Conclusion By using CDSR, the detection capability of observers with little experience improves and is comparable to that of experienced observers. Moreover, the reading time becomes much shorter using CDSR.     

Measurement of liver fat content using selective saturation at 3.0 T

PURPOSE: To validate an MRI technique for measuring liver fat content by calibrating MRI readings with liver phantoms and comparing MRI measurements in human subjects with estimates of liver fat content on liver biopsy specimens. MATERIALS AND METHODS: The MRI protocol consisted of fat and water imaging by selective saturation using a 3.0-T scanner. A water phantom and liver phantoms were scanned before each of 10 human subjects who underwent a liver biopsy to assess for nonalcoholic fatty liver disease (NAFLD). Liver fat content in human subjects was derived from a calibration curve generated by scanning the phantoms. Liver fat was also estimated by optical image analysis and pathologists' assessment of histologic sections. RESULTS: MRI measurements of the liver phantoms were highly reproducible. Measurements of liver fat content in human subjects made by MRI in two areas of the liver were strongly correlated (r=0.98, P<0.001). MRI measurements were highly associated with estimates of liver fat content made by optical image analysis (r=0.96, P<0.001) and with estimates made by the pathologists (r=0.93, P<0.001). CONCLUSION: We validated a technique for quantifying liver fat content based on selective fat and water imaging. The technique is accurate and reproducible and provides a noninvasive method to obtain serial measurements of liver fat content in human subjects.     

Determination of bone mineral content in the heel bone using a gamma camera.

An easy to use and low cost technique for determination of the bone mineral content in the heel bone using an unmodified gamma camera is described. The method uses two small flood phantoms with 125I and 99Tcm, respectively. The precision, when measured on 12 healthy volunteers, was 2.1% and a long-term reproducibility in vitro of 1.8% was obtained on phantoms.     

Online Kidney Position Verification Using Non-Contrast Radiographs on a Linear Accelerator with on Board KV X-Ray Imaging Capability

The kidneys are dose-limiting organs in abdominal radiotherapy. Kilovoltage (kV) radiographs can be acquired using on-board imager (OBI)-equipped linear accelerators with better soft tissue contrast and lower radiation doses than conventional portal imaging. A feasibility study was conducted to test the suitability of anterior-posterior (AP) non-contrast kV radiographs acquired at treatment time for online kidney position verification. Anthropomorphic phantoms were used to evaluate image quality and radiation dose. Institutional Review Board approval was given for a pilot study that enrolled 5 adults and 5 children. Customized digitally reconstructed radiographs (DRRs) were generated to provide a priori information on kidney shape and position. Radiotherapy treatment staff performed online evaluation of kidney visibility on OBI radiographs. Kidney dose measured in a pediatric anthropomorphic phantom was 0.1 cGy for kV imaging and 1.7 cGy for MV imaging. Kidneys were rated as well visualized in 60% of patients (90% confidence interval, 34–81%). The likelihood of visualization appears to be influenced by the relative AP separation of the abdomen and kidneys, the axial profile of the kidneys, and their relative contrast with surrounding structures. Online verification of kidney position using AP non-contrast kV radiographs on an OBI-equipped linear accelerator appears feasible for patients with suitable abdominal anatomy. Kidney position information provided is limited to 2-dimensional “snapshots,” but this is adequate in some clinical situations and potentially advantageous in respiratory-correlated treatments. Successful clinical implementation requires customized partial DRRs, appropriate imaging parameters, and credentialing of treatment staff.     

Conceptus radiation dose and risk from chest screen-film radiography

The objectives of the present study were to (a) estimate the conceptus radiation dose and risks for pregnant women undergoing posteroanterior and anteroposterior (AP) chest radiographs, (b) study the conceptus dose as a function of chest thickness of the patient undergoing chest radiograph, and (c) investigate the possibility of a conceptus to receive a dose of more than 10 mGy, the level above which specific measurements of conceptus doses may be necessary. Thermoluminescent dosimeters were used for dose measurements in anthropomorphic phantoms simulating pregnancy at the three trimesters of gestation. The effect of chest thickness on conceptus dose and risk was studied by adding slabs of lucite on the anterior and posterior surface of the phantom chest. The conceptus risk for radiation-induced childhood fatal cancer and hereditary effects was calculated based on appropriate risk factors. The average AP chest dimension (d_a) was estimated for 51 women of childbearing age from chest CT examinations. The value of d_a was estimated to be 22.3 cm (17.4–27.2 cm). The calculated maximum conceptus dose was 107×10^–3 mGy for AP chest radiographs performed during the third trimester of pregnancy with maternal chest thickness of 27.2 cm. This calculation was based on dose data obtained from measurements in the phantoms and d_a estimated from the patient group. The corresponding average excess of childhood cancer was 10.7 per million patients. The risk for hereditary effects was 1.1 per million births. Radiation dose for a conceptus increases exponentially as chest thickness increases. The conceptus dose at the third trimester is higher than that of the second and first trimesters. The results of the current study suggest that chest radiographs carried out in women at any time during gestation will result in a negligible increase in risk of radiation-induced harmful effects to the unborn child. After a properly performed maternal chest X-ray, there is no need for individual conceptus dose estimations. Electronic Publication     

1995 SMR young investigators' award finalist: MR measurement of time-dependent blood pressure variations

An MR imaging method for measuring intravascular pressure variations is introduced. The technique is based on estimates of vascular compliance and vessel distension, which are obtained from a correlation of spatial and temporal velocity derivatives and measurements of the velocity gradient in the direction of flow, respectively. The accuracy of the technique was determined in vitro through a comparison of MR and transducer pressure measurements obtained in distensible vessel phantoms undergoing pulsatile flow. Results indicated that a root-mean-square error of 4–12% can be expected in phantoms covering a physiological range of compliance. In vivo feasibility was demonstrated by thoracic aorta pressure measurements, which produced pressure waveforms with an expected shape and magnitude.     

In-vitro phantoms for estimating diffusion tensor tractography

No literature has reported on in-vitro diffusion tensor tractography, although it is a useful method to visualize neuronal fiber projections in the living human brain. We applied this technique to phantoms of asparagus stems and bundled polyester yarn, and obtained tractography with high-quality images. On the asparagus stem phantom, straight tracts along the axis were displayed. On the polyester phantom, these tracts followed the course of the bundle whether it was straight or curved. These phantoms are useful for in-vitro evaluation of diffusion tensor tractography.     

Image quality performance of liquid crystal display systems: influence of display resolution, magnification and window settings on contrast-detail detection

The aim of this study was to investigate the combined effects of liquid crystal display (LCD) resolution, image magnification and window/level adjustment on the low-contrast performance in soft-copy image interpretation in digital radiography and digital mammography. In addition, the effect of a new LCD noise reduction mechanism on the low-contrast detectability was studied. Digital radiographs and mammograms of two dedicated contrast-detail phantoms (CDRAD 2.0 and CDMAM 3.4) were scored on five LCD devices with varying resolutions (1-3- and 5-megapixel) and one dedicated 5-megapixel cathode ray tube monitor. Two 5-megapixel LCDs were included. The first one was a standard 5-megapixel LCD and the second had a new (Per Pixel Uniformity) noise reduction mechanism. A multi-variate analysis of variance revealed a significant influence of LCD resolution, image magnification and window/level adjustment on the image quality performance assessed with both the CDRAD 2.0 and the CDMAM 3.4 phantoms. The interactive adjustment of brightness and contrast of digital images did not affect the reading time, whereas magnification to full resolution resulted in a significantly slower soft-copy interpretation. For digital radiography applications, a 3-megapixel LCD is comparable with a 5-megapixel CRT monitor in terms of low-contrast performance as well as in reading time. The use of a 2-megapixel LCD is only warranted when radiographs are analysed in full resolution and when using the interactive window/level adjustment. In digital mammography, a 5-megapixel monitor should be the first choice. In addition, the new PPU noise reduction system in the 5-megapixel LCD devices provides significantly better results for mammography reading as compared to a standard 5-magapixel LCD or CRT. If a 3-megapixel LCD is used in mammography setting, a very time-consuming magnification of the digital mammograms would be necessary.