Dynamic phantom with heart,lung, and blood motion for initial validation of MRI techniques

Purpose:

To develop an anthropomorphic phantom to simulate heart, lung, and blood motion. Magnetic resonance imaging (MRI) is sensitive to image distortion and artifacts caused by motion. Imaging phantoms are used to test new sequences, but generally, these phantoms lack physiological motion. For the validation of new MR‐based endovascular interventional and other techniques, we developed a dynamic motion phantom that is suitable for initial in vitro and more realistic validation studies that should occur before animal experiments.

Materials and Methods:

An anthropomorphic phantom was constructed to model the thoracic cavity, including respiratory and cardiac motions, and moving blood. Several MRI methods were used to validate the phantom performance: anatomical scanning, rapid temporal imaging, digital subtraction angiography, and endovascular tracking. The quality and nature of the motion artifact in these images were compared with in vivo images.

Results:

The closed‐loop motion phantom correctly represented key features in the thorax, was MR‐compatible, and was able to reproduce similar motion artifacts and effects as seen in in vivo images. The phantom provided enough physiological realism that it was able to ensure a suitable challenge in an in vitro catheter tracking experiment.

Conclusion:

A phantom was created and used for testing interventional catheter guiding. The images produced had similar qualities to those found in vivo. This phantom had a high degree of appropriate anthropomorphic and physiological qualities. Ethically, use of this phantom is highly appropriate when first testing new MRI techniques prior to conducting animal studies. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Digital slot-scan charge-coupled device radiography versus AMBER and Bucky screen-film radiography: comparison of image quality in a phantom study

PURPOSE: To evaluate the image quality and performance of a chest digital radiography system and to compare this with the image quality and performance of advanced multiple-beam equalization radiography (AMBER) and Bucky screen-film radiography systems. MATERIALS AND METHODS: The chest digital radiography system is a digital charge-coupled device (CCD) chest imaging unit that uses slot-scan technology. A contrast-detail test object was used in combination with a phantom that simulates the primary and scatter transmission for the lungs and mediastinum. Twelve phantom images were obtained with each modality (ie, CCD digital radiography and AMBER and Bucky screen-film radiography) and were judged by six observers. CCD digital radiography soft-copy reading was compared with AMBER hard-copy reading. To measure image quality, contrast-detail curves were constructed from the observer data. The Wilcoxon signed rank test was used for statistical analysis. RESULTS: For the lung configuration, contrast-detail curves showed lower threshold depth for hard-copy images obtained with CCD digital radiography than for those obtained with Bucky screen-film radiography. For hard-copy images, the difference between contrast-detail curves for CCD digital radiography and those for Bucky screen-film radiography was statistically significant (P < .006). No significant difference was found between CCD digital radiography and AMBER for hard-copy images obtained in either the lung or mediastinum configuration. For the lung configuration, a lower threshold depth was observed for CCD digital radiography soft-copy reading than for AMBER hard-copy reading, with significantly different contrast-detail curves for CCD digital radiography soft copy and AMBER hard copy (P < .006). No significant difference was found between either system for the mediastinum configuration. CONCLUSION: Contrast-detail curves indicate that image quality for the CCD chest system provides a digital alternative to AMBER and Bucky screen-film radiography.     

Digital chest radiography with a solid-state flat-panel x-ray detector: contrast-detail evaluation with processed images printed on film hard copy

PURPOSE: To evaluate and compare human observer performance in a contrast-detail test by using postprocessed hard-copy images from a digital chest radiography system and conventional screen-film radiographs. MATERIALS AND METHODS: The digital radiography system is based on a large-area flat-panel x-ray detector with a structured cesium iodide scintillator layer and an amorphous silicon thin-film transistor array for image readout. Images of a contrast-detail phantom were acquired at two exposure levels by using two standard thoracic screen-film systems and the digital system at matched dose. By using images of the phantom processed with standard chest image postprocessing techniques, a four-alternative forced-choice observer perception study was performed, and the number of detectable test signals (disk-shaped objects 0.3-4.0 mm in diameter) was determined for each image type. RESULTS: On average, observers detected more test signals on digital images than on screen-film radiographs at all diameters up to 2.0 mm and an equivalent number at larger diameters. Test signals with lower inherent subject contrast were detected more readily on digital images than on screen-film images, even when x-ray exposure levels for the digital system were reduced by 20%. CONCLUSION: Observer performance in a contrast-detail detection task can be improved by using images acquired with the flat-panel digital chest radiography system as compared with those acquired with state-of-the-art screen-film combinations.     

Digital radiography of scoliosis with a scanning method: initial evaluation

PURPOSE: To evaluate the radiation dose, image quality, and Cobb angle measurements obtained with a digital scanning method of scoliosis radiography. MATERIALS AND METHODS: Multiple images were reconstructed into one image at a workstation. A low-dose alternative was to use digital pulsed fluoroscopy. Dose measurements were performed with thermoluminescent dosimeters in an Alderson phantom. At the same time, kerma area-product values were recorded. A Monte Carlo dose calculation also was performed. Image quality was evaluated with a contrast-detail phantom and visual grading system. Angle measurements were evaluated with an angle phantom and measurements obtained on patient images. RESULTS: The effective radiation dose was 0.087 mSv for screen-film imaging, 0.16 mSv for digital exposure imaging, and 0.017 mSv for digital fluoroscopy; the corresponding kerma area-product values were 0.43, 0.87, and 0.097 Gy. cm(2), respectively. The image quality of the digital exposure and screen-film images was about equal at visual grading, whereas fluoroscopy had lower image quality. The angle phantom had lower angle values with digital fluoroscopy, although the difference in measured angles was less than 0.5 degrees. The patient images showed no difference in angles. CONCLUSION: The described digital scanning method has acceptable image quality and adequate accuracy in angle measurements. The radiation dose required for digital exposure imaging is higher than that required for screen-film imaging, but that required for digital fluoroscopy is much lower.     

Effect of mechanically simulated diaphragmatic respiratory motion on myocardial SPECT processed with and without attenuation correction.

The goal of this study was to assess the effect of diaphragmatic respiratory motion on inferior wall cold artifact in myocardial SPECT and to assess the ability of attenuation correction (AC) to correct for this artifact in the presence of diaphragmatic motion. METHODS: We used an anthropomorphic phantom with ventricular wall activity, variable ventricular caudal tilt, attenuating liver and spleen cold inserts, and variable vertical (diaphragmatic) motion amplitude and pattern. Cardiac SPECT images were acquired on a gamma camera with dual scanning transmission line sources and commercially available AC software (with scatter correction and iterative reconstruction). The acquired data were processed either using filtered backprojection or with the AC software. The resulting myocardial activity maps were processed with polar plots and with standardized inferior-to-anterior and anterior-to-lateral wall ratios. RESULTS: Subdiaphragmatic attenuation reduces inferior wall counts and this component of inferior wall artifact is fully corrected by AC relative to anterior wall counts both with and without diaphragmatic respiratory motion. In the phantom, diaphragmatic motion artifact manifests as reduction in relative count density in both the anterior wall and the inferior wall relative to the lateral wall, which is not corrected by AC. This artifact becomes more marked with increasing respiratory amplitude and its symmetry depends on the pattern of diaphragmatic motion. CONCLUSION: Images with AC acquired at small respiratory amplitudes (approximately 2 cm) in the phantom resemble images with AC found in published normal patient databases. These results support a clinical need for respiratory gating of myocardial SPECT images.     

Detection of simulated interstitial lung disease and catheters with selenium, storage phosphor, and film-based radiography.

PURPOSE: To evaluate the diagnostic performance of storage phosphor and digital selenium radiography (DSR) with asymmetric and symmetric screen-film systems at different speeds in the detection of simulated interstitial lung disease and catheters. MATERIALS AND METHODS: Patterns of simulated interstitial lung disease and catheters were superimposed over an anthropomorphic chest phantom. Hard-copy images were generated at DSR (200-, 400-, and 600-speed), storage phosphor radiography (200- and 400-speed), and asymmetric (400-speed) and symmetric (200- and 400-speed) screen-film imaging. Surface doses were measured, and receiver operating characteristic analyses were performed. RESULTS: No statistically significant differences were found between the detector systems with the same speeds for each interstitial pattern. Significantly poorer results were found at 600-speed DSR than at 200-speed DSR. Detection of catheters and nodules over high-attenuation areas was significantly worse with the symmetric screen-film system than with the other detectors. The surface dose with the DSR system, without a grid, was about 50% less than that of the other detector systems, with grids, at the same speed. CONCLUSION: No significant difference was found in the diagnostic performance at DSR, storage phosphor radiography, and film-based radiography for simulated interstitial lung disease at corresponding speeds; there was a reduction in the surface dose of about 50% with the 400-speed DSR system.     

Magnification mammography: a comparison of full-field digital mammography and screen-film mammography for the detection of simulated small masses and microcalcifications

The objective of this study was a comparison of a full-field digital mammography (FFDM) system and a conventional screen-film mammography (SFM) system with respect to the detectability of simulated small masses and microcalcifications in the magnification mode. All images were obtained using 1.8 times magnification. The FFDM images were obtained at radiation dose levels of 1.39, 1.0, 0.7, 0.49 and 0.24 times that of the SFM images. A contrast-detail phantom was used to compare the detection of simulated lesions using a four alternative forced-choice reader study with three readers. The correct observation ratio (COR) was calculated as the fraction of correctly identified lesions to the total number of simulated lesions. Soft-copy reading was performed for all digital images. Direct magnification images acquired with the digital system showed a lower object contrast threshold than those acquired with the conventional system. For equal radiation dose, the digital system provided a significantly increased COR (0.95) compared with the screen-film system (0.82). For simulated microcalcifications, the corresponding difference was 0.90 to 0.72. The digital system allowed equal detection to screen-film at 40% of the radiation dose used for screen film. Digital magnification images are superior to screen-film magnification images for the detection of simulated small masses and microcalcifications even at a lower radiation dose.     

Digital slot-scan charge-coupled device radiography versus AMBER and Bucky screen-film radiography for detection of simulated nodules and interstitial disease in a chest phantom

PURPOSE: To evaluate the diagnostic performance of full-field slot-scan charge-coupled device (CCD)-based digital radiography in the detection of simulated chest diseases in clinical conditions versus that of two screen-film techniques: advanced multiple beam equalization radiography (AMBER) and Bucky radiography. MATERIALS AND METHODS: Simulated nodules and interstitial nodular and interstitial linear lesions were attached onto an anthropomorphic chest phantom. One hundred sixty-eight lesions were distributed over 25 configurations. A posteroanterior chest radiograph of each configuration was obtained with each technique. The images were presented to six observers. Each lesion was assigned one of two outcome scores: "detected" or "not detected." False-positive readings were evaluated. Differences between the imaging methods were analyzed by using a semiparametric logistic regression model. RESULTS: For simulated nodules and interstitial linear disease, no statistically significant difference was found in diagnostic performance between CCD digital radiography and AMBER. The detection of simulated interstitial nodular disease was better with CCD digital radiography than with AMBER: Sensitivity was 71% (77 of 108 interstitial nodular lesions) with CCD digital radiography but was 56% (60 of 108 lesions) with AMBER (P =.041). Better results for the detection of all lesion types in the mediastinum were observed with CCD digital radiography than with Bucky screen-film radiography: Sensitivity was 45% (227 of 504 total simulated lesions) with CCD digital radiography but was 24% (119 of 504 lesions) with Bucky radiography (P <.001). There were fewer false-positive observations with CCD digital radiography (35 [5.7%] of 609 observations) than with Bucky radiography (47 [9.5%] of 497 observations; P =.012). CONCLUSION: Differences were in favor of the full-field slot-scan CCD digital radiographic technique. This technique provides a digital alternative to AMBER and Bucky screen-film radiography.     

Simulated bone erosions in a hand phantom: detection with conventional screen-film technology versus cesium iodide-amorphous silicon flat-panel detector

PURPOSE: To assess the diagnostic performance of an active-matrix flat-panel x-ray detector for reduced-dose imaging of simulated arthritic lesions. MATERIALS AND METHODS: A digital x-ray detector based on cesium iodide and amorphous silicon technology with a panel size of 43 x 43 cm, matrix of 3,000 x 3,000 pixels, pixel size of 143 micrometer, and digital output of 14 bits was used. State-of-the-art screen-film radiographs were compared with digital images obtained at doses equivalent to those obtained with system speeds of 400, 560, and 800. The phantom was composed of a human hand skeleton on an acrylic plate with drilled holes simulating bone erosions of different diameters and depths. Results of four independent observers were evaluated with receiver operating characteristic curve analysis. RESULTS: The cesium iodide and amorphous silicon detector resulted in better diagnostic performance than did the screen-film combination, with the dose being the same for both modalities (P <.05). For digital images obtained at reduced doses, no significant differences were found. CONCLUSION: The improved diagnostic performance with digital radiographs obtained with the cesium iodide and amorphous silicon detector suggests that this detector technology holds promise in terms of dose reduction for specific diagnostic tasks, without loss of diagnostic accuracy.     

Patient absorbed doses in digital grey-scale fluorography

This article describes a preliminary comparison between the levels of patient dose used in digital grey-scale fluorography (DGF) and screen-film radiography. Patient doses were measured in three common radiographic examinations, postero-anterior chest, antero-posterior lumbar spine and lateral lumbo-sacral junction, using thermoluminescent dose-meters and an anthropomorphic phantom. Within the limitations of the image quality currently available in DGF, the findings indicate that digital radiography with the large-field X-ray image intensifier promises significant savings in patient dose compared with conventional radiography.     

Storage phosphor and film-screen mammography: performance with different mammographic techniques

The aim of this study was to compare the image quality of storage phosphor plates with that in screen-film radiograms in mammography. Two anode/filter combinations were also compared – Mo/Mo and W/Rh. S Storage phosphor plates, generation IIIN (Fuji, Tokyo, Japan) and a conventional screen-film system (Kodak, Rochester, N. Y.) were evaluated using two mammographic units. One unit had a 0.6-mm focal spot, an anode/filter combination of Mo/Mo and no grid (A_Mo); the other had a 0.3-mm focal spot, a grid, and two possible combinations of anode/filter Mo/Mo (B_Mo) and W/Rh (B_W). Simulated tumours and microcalcifications were randomly positioned in an anthropomorphic breast phantom (RMI model 165, no. 210–009, Radiation Measurements Inc., Middleton, Wisconsin). The image quality was evaluated using a modified version of receiver operating characteristics analysis. Five observers evaluated 300 films and 300 hard copy images each. Radiation doses were also determined. The image quality of the conventional screen-film images was significantly better than that for the storage phosphor plate mammograms. The B_Mo system rated best, for the detection of both tumours and microcalcifications, although it was not significantly different from the B_W system. Systems B_Mo and B_W rated significantly better than the A_Mo system for both image receptors studied. The mean absorbed dose was twice as high for the B_Mo system as for the A_Mo and B_W systems for both conventional and digital technique. The mammograms produced with the screen-film combination gave a significantly better detectability than the storage phosphor plates used in this study. Substantial dose reduction could be achieved using an anode/filter combination of W/Rh instead of Mo/Mo with no significant loss of information in the images. Received 6 June 1997; Revision received 22 August 1997; Accepted 10 July 1998     

Boundary artifact due to truncation errors in MR imaging

A boundary artifact in MR images due to truncation of the infinite Fourier series necessary to encode tissue discontinuities was investigated by using doped water phantoms and normal volunteers. All images were obtained on 0.3-T permanent and 0.6-T superconducting MR imagers with varying phase and frequency sampling rates. The artifact appeared in both the phase and frequency encoding direction as parallel lines or ringing adjacent to borders or tissue discontinuities. This was unlike motion artifacts, which occur predominantly in the phase direction, and chemical shift misregistration errors, which are most pronounced in the frequency direction. Increasing the sampling frequency from 128 to 512 resulted in higher frequency ringing and more rapid drop-off in amplitude. Low-pass digital filtering also decreased the ringing at the expense of fine detail. The truncation of the infinite Fourier series necessary to encode edges to the 128-512 terms used for most MR imaging produces the artifact. It is important to recognize this common artifact and not mistake it for patient motion or disease.     

The first trial of phase contrast imaging for digital full-field mammography using a practical molybdenum x-ray tube

RATIONALE AND OBJECTIVES: The image quality of a newly developed full-field digital phase contrast mammography (PCM) system and of a conventional screen-film (SF) mammography system were compared via images of a phantom and receiver operating characteristic (ROC) analysis of clinical images. METHODS: Magnified (1.75X) PCM images were scanned (sampling rate, 43.75 microm) and then reduced to original-sized, 25-micron pixel images printed on photothermographic film. Along with corresponding SF images, the phantom images were evaluated subjectively, and the clinical images of 38 patients were subjected to ROC analysis of mass and microcalcification. RESULTS: In the image quality of a phantom, the PCM exceeded the SF. In both mass and microcalcification, the ROC analysis Az values of the PCM clinical images surpassed those of the SF images. CONCLUSION: The PCM provides better images than the SF. Clinical trials suggest superior detection of both mass and microcalcification by full-field digital PCM over conventional SF mammography.     

Comparison between a screen-film system and a selenium radiography system. An ROC study using simulated thoracic lesions

RATIONALE AND OBJECTIVES: To evaluate the diagnostic image quality of the hard copies of a commercially available selenium detector-based computed radiography system compared to that of a conventional screen-film system. METHODS: Ten radiographs of an anthropomorphic chest phantom with simulated nodular and linear-reticular lesions were produced using either system. Each radiograph was subdivided into 15 fields containing zero lesions, one nodular lesion, one linear-reticular lesion, or both lesions. The total of 150 fields for each modality was reviewed by six radiologists, and receiver operating analysis was performed. RESULTS: The conventional screen-film system performed significantly better for nodular lesions, whereas no statistically significant difference was found between the detection rates of both systems for linear-reticular lesions. CONCLUSIONS: The better detection of nodules with the dedicated selenium detector can be explained by the higher dynamic range of the system. Detection of linear-reticular lesions was slightly but not significantly better with the screen-film system, but the detection rate of the selenium detector might be further improved with a different image processing technique.     

Dose reduction in full-field digital mammography: an anthropomorphic breast phantom study

The aim of this study was to evaluate the potential for radiation dose reduction by using other beam qualities in full-field digital mammography (FFDM) compared with screen-film mammography (SFM). FFDM was performed using an amorphous silicon detector with a caesium iodide scintillator layer (Senographe 2000D, GE, Milwaukee, USA). SFM was performed using a state-of-the-art conventional system (Senographe DMR, GE, Milwaukee, USA) with a dedicated screen-film combination. An anthropomorphic breast phantom with superimposed microcalcifications (50-200 microm) was used to evaluate the detectability of microcalcifications. Contact mammograms and magnification views (m=1.8) performed with both the digital and the screen-film system were compared. Images were exposed automatically. Molybdenum/Molybdenum (Mo/Mo) anode-filter combination, 28 kVp and 63 mAs were selected by the automatic optimization of parameters (AOP) of the conventional system. This exposure protocol (protocol A) was also used as baseline for the digital system. Dose reduction in digital mammography was achieved by using protocol B with Mo/Rh and 31 kVp and protocol C with Rh/Rh and 32 kVp. The detectability of microcalcifications was assessed by 3 experienced readers with a confidence level ranging from 1 to 5. A receiver operating characteristic (ROC) analysis was performed. In protocol A the area under the ROC-curve (A(z)) for contact views performed by the screen-film system was 0.64 and for those performed with the FFDM system 0.68. The A(z) values were 0.74 in protocol B and 0.65 in protocol C for the digital system. For the conventional and digital magnification views A(z) values were 0.71 and 0.79, respectively. For protocol B the A(z) value was 0.81 and for protocol C it was 0.76. There is no statistically significant difference in the A(z) values for the different protocols in digital mammography and no significant difference from the screen-film system. A potential for dose reduction by using other beam qualities seems to be possible with this digital system.     

Digital chest radiography with a large image intensifier. An ROC study with an anthropomorphic phantom

The diagnostic performance of two systems for chest radiography was studied. One system was based on a large image intensifier, the other was a conventional film-screen system. The images from the image intensifier were studied either on a digital TV screen or on 100 mm photofluorograms. Receiver operating characteristic curve analysis was performed on images of an anthropomorphic chest phantom. Low-contrast MMAP (methyl methacrylate polymer) nodules and simulated vessels were positioned over the parenchymal and the mediastinal region of the phantom. Five observers assessed the digital monitor images, photofluorograms, and conventional full-size radiograms. The results showed a significantly superior detectability for the full-size radiograms over the digital monitor images both in the parenchyma and in the mediastinum. No significant difference was found between photofluorograms and digital images.     

Optimization of the chest exposure condition with a contrast-detail phantom: evaluation of the flat-panel versus computed radiography systems

In this study, we evaluated the performance of a digital chest imaging system using a contrast-detail (C-D) phantom. In the initial step, 76 sample images of the C-D phantom were produced by changing the doses from 0.5, 0.75, 1.0, 1.25, 1.5, to 2.0 times the dose for a screen-film (S/F) system. The sample images were analyzed by five radiological technologists and two medical physicists, and the image quality figure (IQF) was determined. The quality of each image was examined, and appropriate doses were determined from the calculated IQF to obtain the same image quality for other digital chest imaging systems. The method of determining IQF from C-D phantom analysis was very useful for comparing image quality and determining radiographic techniques.     

Scoliosis examinations: organ dose and image quality with rare-earth screen-film systems

We determined the dose to the breast and evaluated the image quality when various high-speed, rare-earth screen-film systems were used in conjunction with breast dose reduction methods in children undergoing scoliosis examinations. In addition, normalized organ dose to the breast, active bone marrow, thyroid, eyes, ovaries, and testes were measured in a pediatric anthropomorphic phantom comparing the anteroposterior and posteroanterior projections. The average measured dose to the breast was 6.9 and 4.0 mrad (10(-5) Gy), respectively, for nominal 400- and 600-speed, rare-earth screen-film systems used in combination with breast dose reduction methods. The image quality of these systems as evaluated by three radiologists was rated as adequate. The dosimetry results with an anthropomorphic phantom showed that the posteroanterior projection provides approximately a threefold reduction in breast dose as compared with the anteroposterior view. However, the dose to the bone marrow is doubled. Rare-earth screen-film systems used in combination with simple dose-reduction methods can provide adequate image quality for scoliosis examination while significantly reducing the radiation dose to the breast.     

Flat-panel x-ray detector based on amorphous silicon versus asymmetric screen-film system: phantom study of dose reduction and depiction of simulated findings

PURPOSE: To compare a large-area amorphous silicon flat-panel detector with an asymmetric screen-film system for the depiction of simulated patterns of interstitial lung disease, nodules, and catheters, as well as for evaluation of dose reduction. MATERIALS AND METHODS: Ground-glass, linear, miliary, and reticular patterns; nodules; and catheters were superimposed over an anthropomorphic chest phantom. Hard copies were generated at different dose levels (speeds: 400, 800, and 1,600) with a flat-panel detector and were compared with copies generated with an asymmetric screen-film system (speed, 400). Detection performance of eight radiologists was compared with a receiver operating characteristic analysis of 19,200 observations per pattern. A difference was significant with a P value of.05. RESULTS: There was no statistically significant difference between the flat-panel detector and the asymmetric screen-film system at the same speed (P >.05) and between the flat-panel detector at a speed of 800 and the asymmetric screen-film system at a speed of 400 (P >.05). The visibility of linear, miliary, and reticular patterns over lucent lung and of nodules smaller than 10 mm and catheters over obscured chest regions on copies generated at a speed of 1,600 with the flat-panel detector decreased, compared with the visibility of these features on copies generated with the asymmetric screen-film system (P <.05). CONCLUSION: The diagnostic performance of the flat-panel detector is comparable to that of the asymmetric screen-film system for depiction of all simulated patterns of interstitial lung diseases, nodules, and catheters at the same speed and offers the potential of dose reduction to a speed of 800.     

Digital and conventional chest imaging: a modified ROC study of observer performance using simulated nodules

A modified receiver operating characteristic (ROC) study was performed in which five readers were asked to locate multiple nodules on images of an anthropomorphic phantom obtained with a prototype digital radiographic chest unit and with a conventional chest unit. Results indicate that when nodules were projected over the lungs, a significantly greater number (significant at the 5% level) were identified on conventional radiographs, whereas for nodules projected over the mediastinum, the digital images were notably superior (difference significant at the 2% level). An error analysis of the multiple nodule problem and pseudo-ROC curves are presented. The modified ROC study does not suffer from the positional ambiguity inherent in most ROC studies and is efficient in acquiring data.