The potential of dynamic 99mTc-sestamibi cadmium zinc telluride-single-photon emission computed tomography camera assessing myocardial flow reserve in patients with heart failure with preserved ejection fraction.

Aims: Coronary microvascular dysfunction (CMD) is related to the pathophysiology, mortality, and morbidity of heart failure with preserved ejection fraction (HFpEF). A novel single-photon emission computed tomography (SPECT) camera with cadmium zinc telluride (CZT) detectors allows for the quantification of absolute myocardial blood flow and myocardial flow reserve (MFR) in patients with coronary artery disease. However, the potential of CZT-SPECT assessing for CMD has never been evaluated in patients with HFpEF. Methods and results: The clinical records of 127 consecutive patients who underwent dynamic CZT-SPECT were retrospectively reviewed. Rest and stress scanning were started simultaneously with 3 and 9 MBq/kg of 99mTc-sestamibi administration, respectively. Dynamic CZT-SPECT imaging data were analysed using a net-retention model with commercially available software. Transthoracic echocardiography was performed in all patients. The MFR value was significantly lower in the HFpEF group (mean ± SEM = 2.00 ± 0.097) than that in the non-HFpEF group (mean ± SEM = 2.74 ± 0.14, P = 0.0004). A receiver operating characteristic analysis indicated that if a cut-off value of 2.525 was applied, MFR could efficiently distinguish HFpEF from non-HFpEF. Heart failure with preserved ejection fraction had a consistently low MFR, regardless of the diastolic dysfunction score. Heart failure with preserved ejection fraction patients with MFR values lower than 2.075 had a significantly higher incidence of heart failure exacerbation. Conclusion: Myocardial flow reserve assessed by CZT-SPECT was significantly reduced in patients with HFpEF. A lower MFR was associated with a higher hospitalization rate in these patients. Myocardial flow reserve assessed by CZT-SPECT has the potential to predict future adverse events and stratify the severity of disease in patients with HFpEF.

Detection of coronary artery disease using automated quantitation of myocardial perfusion on single-photon emission computed tomography images from patients with angina pectoris without prior myocardial infarction.

BACKGROUND: Whether or not automated scores obtained from myocardial single-photon emission computed tomography (SPECT) imaging using software correlate with the visual interpretations by experts remains obscure. METHODS AND RESULTS: Eighty-seven consecutive patients with known or suspected angina pectoris underwent (201)thallium stress/rest SPECT followed by coronary angiography and the summed difference scores (SDS) were calculated using Heart Score View software. The SDS was substantially associated with coronary stenosis and accurately detected culprit lesions, because the diagnostic accuracy was comparable to that of expert visual evaluation. CONCLUSIONS: Automated scores obtained from myocardial SPECT can help detect coronary artery disease.

Quantification of image quality using information theory.

Aims of present study were to examine usefulness of information theory in visual assessment of image quality. We applied first order approximation of the Shannon's information theory to compute information losses (IL). Images of a contrast-detail mammography (CDMAM) phantom were acquired with computed radiographies for various radiation doses. Information content was defined as the entropy Σp( i )log(1/p ( i )), in which detection probabilities p ( i ) were calculated from distribution of detection rate of the CDMAM. IL was defined as the difference between information content and information obtained. IL decreased with increases in the disk diameters (P < 0.0001, ANOVA) and in the radiation doses (P < 0.002, F-test). Sums of IL, which we call total information losses (TIL), were closely correlated with the image quality figures (r = 0.985). TIL was dependent on the distribution of image reading ability of each examinee, even when average reading ratio was the same in the group. TIL was shown to be sensitive to the observers' distribution of image readings and was expected to improve the evaluation of image quality.

Detectability of the diagonal direction in the assessment of medical images using a high-brightness liquid crystal display monitor.

Liquid crystal display (LCD) monitors show a homogenous quadratic pattern in the number of pixels, size, and dimensions. However, their modulation transfer function (MTF) has a non-isotropic effect in the vertical, horizontal, and diagonal directions on the screen from the shape and pattern of arrangement of pixels. Moreover, the MTF of the human eye differs in spatial frequency response directivity among individuals. In this study, the high-brightness LCD monitor detectability was physically simulated and visually examined throughout the system, including the imaging system. Furthermore, the influence of anisotropy of the LCD monitor was evaluated. The MTF of the LCD monitor was measured by acquiring a bar pattern using a digital camera with sufficiently small pixels in the vertical, horizontal, and diagonal directions and by performing interpolation processing through waveform reproduction and frequency analysis. The detectability of the LCD monitor was verified throughout the system, including the imaging system. Radiographs of the rectangular wave chart (0.5-10 LP/mm) were obtained in the vertical, horizontal, and diagonal (45°) directions to assess the perceivable limit of the human eye (LP/mm). The spatial resolution of the LCD monitor in the diagonal direction was higher than that in the vertical or horizontal direction, which was in good agreement with the results of the profile analysis and visual evaluation.

Statistical characteristics of streak artifacts on CT images: relationship between streak artifacts and mA s values.

The purpose of this study is to investigate how streak artifacts on computed tomography (CT) images vary with reduction in radiation doses by assessing the quantitative relationship between the streak artifacts and milliampere-time product (mA s) values. A commercially available chest phantom was used to measure the streak artifacts on the CT images obtained using a 4- and 16-multidetector-row helical CT scanners with various mA s values at a constant tube voltage of 120 kVp. The cardiac slice image was employed as a target image for evaluating the streak artifacts on the CT image. Eighty parallel line segments with a length of 20 pixels were placed perpendicular to numerous streak artifacts on the cardiac slice image, and the largest difference between adjacent CT values in each of the 80 CT-value profiles of these line segments was employed as a feature variable of streak artifacts; these feature variables have been analyzed by the extreme value theory. The largest difference between adjacent CT values in each CT-value profile can be statistically modeled by a Gumbel distribution. Further, the maximum level of streak artifacts on CT images that will be tolerated for clinical use and low-dose CT screening examination was expected to be estimated using the location parameter in the Gumbel distribution.

Comparative Cardiac Phantom Study Using Tc-99m/I-123 and Tl-201/I-123 Tracers with Cadmium-Zinc-Telluride Detector-Based Single-Photon Emission Computed Tomography.

OBJECTIVE: A recently introduced single-photon emission computed tomography (SPECT), based on cadmium-zinc-telluride (CZT) detectors (D-SPECT), supports high energy resolution for cardiac imaging. Importantly, the high energy resolution may allow simultaneous dual-isotope (SDI) imaging (e.g., using Tc-99m and I-123). We quantitatively evaluated Tc-99m/I-123 SDI imaging by D-SPECT in comparison with conventional T1-201/I-123. MATERIALS AND METHODS: Energy resolution was measured as a percentage of the full width at half maximum (FWHM) for Tc-99m, I-123, and Tl-201. The impact of cross-talk and reconstructed image contrast were quantified by measuring the contrast-to-noise ratio (CNR), and the transmural defect contrast in the left ventricle wall (C TD) induced by a difference in energy, for combinations of Tc-99m/I-123 or Tl-201/I-123, using an RH-2 cardiac phantom. Corresponding measurement was also carried out in Anger SPECT (A-SPECT). RESULTS: The energy resolution of the D-SPECT system was 5.4%/5.1% for Tc-99m/I-123 and 5.4%/5.3% for Tl-201/I-123, which was approximately two times higher than the A-SPECT. No notable difference was confirmed in the CNRs of the two systems, but T1-201/I-123 showed overall higher value than Tc-99m/I-123. Compared to A-SPECT, C TD of D-SPECT significantly increased with both Tc-99m/I-123 and T1-201/I-123 (p < 0.05). In DSPECT, the combination of Tc-99m/I-123 had a slightly better C TD than T1-201/I-123. In addition, C TD of Tc-99m/I-123 was improved with scatter correction at both nuclides (p < 0.05), but in Tl-201/I-123, no significant improvement was confirmed in I-123 (p > 0.05). CONCLUSION: D-SPECT was considered to be capable of performing high-quality SDI imaging using Tc-99m/I-123.

Quantitative assessment of the influence of anatomic noise on the detection of subtle lung nodule in digital chest radiography using fractal-feature distance.

PURPOSE: To confirm whether or not the influence of anatomic noise on the detection of nodules in digital chest radiography can be evaluated by the fractal-feature distance. MATERIALS AND METHODS: We used the square images with and without a simulated nodule which were generated in our previous observer performance study; the simulated nodule was located on the upper margin of a rib, the inside of a rib, the lower margin of a rib, or the central region between two adjoining ribs. For the square chest images, fractal analysis was conducted using the virtual volume method. The fractal-feature distances between the considered and the reference images were calculated using the pseudo-fractal dimension and complexity, and the square images without the simulated nodule were employed as the reference images. We compared the fractal-feature distances with the observer's confidence level regarding the presence of a nodule in plain chest radiograph. RESULTS: For all square chest images, the relationships between the length of the square boxes and the mean of the virtual volumes were linear on a log-log scale. For all types of the simulated nodules, the fractal-feature distance was the highest for the simulated nodules located on the central region between two adjoining ribs and was the lowest for those located in the inside of a rib. The fractal-feature distance showed a linear relation to an observer's confidence level. CONCLUSION: The fractal-feature distance would be useful for evaluating the influence of anatomic noise on the detection of nodules in digital chest radiography.

Fractal-feature distance as a substitute for observer performance index in contrast-detail examination.

PURPOSE: To assess whether or not the fractal-feature distance using the box-counting algorithm can be a substitute for observer performance index. METHODS AND MATERIALS: Contrast-detail (C-D) phantom images were obtained at various mAs-values (0.5-4.0 mAs) and 140 kV(p) with a Fuji computed radiography system, and the reference image was acquired at 50 mAs; all cylindrical targets in the C-D phantom were visualized on this image. The C-D images were converted to binary images using the profile curves around the smallest cylindrical target images on the reference images. The fractal analysis was conducted using the box-counting algorithm for these binary images. The fractal-feature distances between the low-dose and reference images were calculated using the fractal dimension and the complexity. Furthermore, we performed the C-D analysis in which ten radiologists participated, and compared the fractal-feature distances with the image quality figures (IQF) derived from the C-D analysis with Markov chain. RESULTS: For all C-D phantom radiographs, the relationship between the length of the square boxes and the number of boxes to cover the positive pixels of the binary image was linear on a log-log scale (r>or=0.999). A strong linear correlation was found between the fractal-feature distance and IQF (r=0.990). CONCLUSION: We have shown that the binary image of C-D phantom can be analyzed by the box-counting algorithm and its fractal-feature distance increases as the radiation dose decreases. Furthermore, we have shown that the fractal-feature distances will be equivalent to IQFs in C-D analysis.

Fractal-feature distance analysis of radiographic image.

RATIONALE AND OBJECTIVES: We have conducted a fractal analysis of low-dose digital chest phantom radiographs and evaluated the relationship between the fractal-feature distance and the tube current-exposure time product. MATERIALS AND METHODS: Chest phantom radiographs were obtained at various mAs values (0.5-4.0 mAs) and 140 kVp with a computed radiography system, and the reference images were acquired at 13 mAs. The lung field images were converted to binary images after processing them using the rolling-ball technique; a fractal analysis was conducted using the box-counting method for these binary images. The fractal-feature distances between the low-dose and reference images were calculated using the fractal dimension and the complexity. RESULTS: For all binary images of lung fields, the relationship between the length of the square boxes and the number of boxes needed to cover the positive pixels of the binary image was linear on a log-log scale (r > or = 0.99). For mAs > or = 3.0, the fractal-feature distances were almost constant, whereas for mAs < or = 2.5, they increased depending on the reduction in mAs values. CONCLUSION: We have shown that a binary image of the lung field obtained from a chest phantom radiograph can be analyzed by the box-counting method and that its fractal-feature distance grows as the radiation dose declines.

Information loss in visual assessments of medical images.

We applied information theory to quantify information losses in assessing contrast-detail (C-D) analysis. Images of a C-D phantom were acquired with a flat panel detector (FPD) and a computed radiography (CR) by changing surface entrance doses. Six phantom radiographs (FPD: five images; CR: one image) were prepared for visual evaluations. Thirteen radiographers and two radiologists participated in the observation test. Detectability was defined as the shortest length of the cylinders of which border the observers could recognize from the background, and was recorded using row number. Information content was defined as the entropy summation operatorp(i)log(1/p(i)) with detection probabilities p(i), which were calculated from distribution of detection rate of the ith column. Information loss, in unit of bits, was calculated as the difference between information obtained and information content when all the columns were detected. The information losses decreased with the increase in cylinder diameters and with the increase in surface entrance dose. Because the information loss varies depending on distribution of detection rate, this method of using the information theory was expected to be more sensitive in evaluating the C-D image quality than using the averaged values of detectability.

Quantification of Contraction Synchronicity and Contraction Work in Coronary Artery Disease.

PURPOSE: This study quantified the contraction synchronicity (CS; with 100% representing full synchrony and -100% dyssynchrony) and contraction work (CW, millijoules per centimeter squared; representing myocardial area) in patients with reduced left ventricular ejection fraction (LVEF) associated with coronary artery disease (CAD). METHODS: CS, CW and LVEF in 104 subjects (54 CAD patients and 50 control subjects without CAD) were measured using rest electrocardiography-gated single-photon emission computed tomography (ECG SPECT). Contraction amplitude (CA), synchronous contraction index (SCI), and CW were evaluated using the program Quantification of Segmental Function by Solving the Poisson Equation (QSFP) developed in-house. RESULTS: The mean CA, SCI and CW of 17 segments in the control subjects were 33.8 ± 4.1% (±SD), 96.6 ± 1.4%, and 6.9 ± 1.0 mJ/cm2, respectively. In the patients with CAD, the respective values were 26.1 ± 7.3%, 82.1 ± 16.8%, and 5.4 ± 1.6 mJ/cm2. In the CAD patients with LVEF <40% (n = 14), the mean CA, SCI,and CW were 17.9 ± 4.0%, 63.0 ± 18.4%, and 3.5 ± 1.1 mJ/cm2, respectively. These values were significantly lower than in the control subjects (p < 0.005). Using receiver operating characteristic analysis, values for the area under the curve showing the performance of CA, CS, CW and LVEF in the diagnosis of CAD were 0.81, 0.86, 0.78, and 0.84, respectively. CONCLUSION: Asynchrony shown using the QSFP is useful for CAD detection.

Evaluation of Cadmium-Zinc-Telluride Detector-based Single-Photon Emission Computed Tomography for Nuclear Cardiology: a Comparison with Conventional Anger Single-Photon Emission Computed Tomography.

PURPOSE: The differences in performance between the cadmium-zinc-telluride (CZT) camera or collimation systems and conventional Anger single-photon emission computed tomography (A-SPECT) remain insufficient from the viewpoint of the user. We evaluated the performance of the D-SPECT (Spectrum Dynamics, Israel) system to provide more information to the cardiologist or radiological technologist about its use in the clinical field. MATERIALS AND METHODS: This study evaluated the performance of the D-SPECT system in terms of energy resolution, detector sensitivity, spatial resolution, modulation transfer function (MTF), and collimator resolution in comparison with that of A-SPECT (Bright-View, Philips, Japan). Energy resolution and detector sensitivity were measured for Tc-99m, I-123, and Tl-201. The SPECT images produced by both systems were evaluated visually using the anthropomorphic torso phantom. RESULTS: The energy resolution of D-SPECT with Tc-99m and I-123 was approximately two times higher than that of A-SPECT. The detector sensitivity of D-SPECT was higher than that of A-SPECT (Tc-99m: 4.2 times, I-123: 2.2 times, and Tl-201: 5.9 times). The mean spatial resolution of D-SPECT was two times higher than that of A-SPECT. The MTF of D-SPECT was superior to that of the A-SPECT system for all frequencies. The collimator resolution of D-SPECT was lower than that of A-SPECT; however, the D-SPECT images clearly indicated better spatial resolution than the A-SPECT images. CONCLUSION: The energy resolution, detector sensitivity, spatial resolution, and MTF of D-SPECT were superior to those of A-SPECT. Although the collimator resolution was lower than that of A-SPECT, the D-SPECT images were clearly of better quality.

The application of Markov theory to contrast-detail analysis.

RATIONALE AND OBJECTIVES: To improve the accuracy of contrast-detail (C-D) analysis, we have devised a new evaluation method of the detection performance in the C-D analysis by using the Markov process model. This article describes this new evaluation method and the results of applying it to the illustrative examples. MATERIALS AND METHODS: A commercially available C-D phantom was employed as a test object, and 20 phantom radiographs with an average background density of 0.8 were prepared. Thirty-five observers interpreted all phantom radiographs independently of each other with the room lights off. We assume the Markov model in which the selection of the smallest visible contrast for each row of disks with the same diameter depends only on the contrast selected as the smallest visible one for the same row in the just-before reading experiment. By using this Markov model, the contrast detectability for each disk diameter was calculated, and a C-D diagram was constructed based on these results. The conventional C-D diagram was also derived from the averages of contrast detectability obtained from the interpretations of all phantom radiographs. RESULTS: All C-D diagrams obtained from our devised method agreed well with each other and were in good accord with the conventional C-D diagram from the interpretations of all phantom radiographs. CONCLUSIONS: We have devised a new evaluation method of C-D analysis by using the Markov model and have shown this method will be consistent with the conventional evaluation method in the C-D analysis.

A method of clustering observers with different visual characteristics.

Evaluation of observer's image perception in medical images is important, and yet has not been performed because it is difficult to quantify visual characteristics. In the present study, we investigated the observer's image perception by clustering a group of 20 observers. Images of a contrast-detail (C-D) phantom, which had cylinders of 10 rows and 10 columns with different diameters and lengths, were acquired with an X-ray screen-film system with fixed exposure conditions. A group of 10 films were prepared for visual evaluations. Sixteen radiological technicians, three radiologists and one medical physicist participated in the observation test. All observers read the phantom radiographs on a transillumination image viewer with room lights off. The detectability was defined as the shortest length of the cylinders of which border the observers could recognize from the background, and was recorded using the number of columns. The detectability was calculated as the average of 10 readings for each observer, and plotted for different phantom diameter. The unweighted pair-group method using arithmetic averages (UPGMA) was adopted for clustering. The observers were clustered into two groups: one group selected objects with a demarcation from the vicinity, and the other group searched for the objects with their eyes constrained. This study showed a usefulness of the cluster method to select personnels with the similar perceptual predisposition when a C-D phantom was used in image quality control.

Improvement of Left Ventricular Asynchrony: Cases of Functional Recovery After Revascularization.

Assessment of regional contraction is considered important for diagnosis of coronary artery disease (CAD). We evaluated the synchronicity in regional contraction and assessed recovery from contraction insufficiency after revascularizations. Myocardial contraction parallel to the left ventricular (LV) wall was calculated using the method called quantification of segmental function by solving the Poisson equation (QSFP) from an electrocardiogram (ECG)-gated (99m)Tc-methoxyisobutylisonitrile (MIBI) single-photon emission computed tomographic (ECG-SPECT) image. Myocardial synchronous contraction was quantified using the synchronous contraction index (SCI), defined as the temporal correlation coefficient between LV volume and regional myocardial shortening. SCI was evaluated in 20 subjects, of whom 10 had CAD and 10 were normal. ECG-SPECT was performed in all the CAD patients before and after revascularization. In the 10 patients with CAD, the mean SCI before the revascularization was 62.7 ± 19.1%, which was significantly lower than that in the normal subjects (95.0 ± 3.0%, p = 0.002). After revascularization, a significant improvement in SCI was recorded (74.8 ± 11.1%, p = 0.01). The territorial improvement in SCI was 12.0 ± 15.6% (p = 0.03). Locations of abnormal cardiac contraction due to CAD were delineated by using QSFP. Therefore, SCI can be considered a valuable index for cardiac function assessment.

[Grouping of observer's visual characteristics on the basis of difference in the criteria of visual detection and selection of the fittest clustering method:verification of observer's group with radiologist-like visual characteristics].

Various clustering methods are used in cluster analyses, with each clustering method demonstrating unique advantages. Therefore, it is important to make the best use of the advantages each method provides. We have recognized that it is necessary in the evaluation of X-ray images to classify observers quantitatively according to visual characteristics (grouping of observers) and have clustered observers using the UPGMA method, which is one of the clustering methods. We found that the observers were clustered into two different groups, one with radiologist-like characteristics and the other with medical physicist-like characteristics. Furthermore, we suggested that the group with radiologist-like characteristics was suitable for QC of X-ray images. However, it is doubtful whether the UPGMA method is most suitable for the grouping of observers. In this work we clustered observers using various clustering methods and examined the most suitable method for the evaluation of X-ray images. The results showed that the ward method was least suitable for the grouping of observers, and they were distinctly grouped into two different categories by using a further method.

[Classification of observer-groups with cluster analysis and the criteria of visual decision for each group].

It is important that the evaluation of X-ray images include the observer's visual characteristics. However, evaluations of X-ray images that include these characteristics are not performed because of the difficulty of quantitatively elucidating visual characteristics. In this study, we classified observers into groups (clusters) by the same criteria of visual decision, using cluster analysis (unweighted Pair-Group method using arithmetic averages), and evaluated X-ray images on the basis of this separation. Clinical application is also discussed. It was found that observer clustering caused a decrease in between-observer variation. Observers were grouped into two different categories: one with the characteristics of radiologists and the other with the characteristics of medical physicists. Our results indicated that the group with the characteristics of radiologists was suitable for the quality control (QC) of X-ray images.

A detection method for streak artifacts and radiological noise in a non-uniform region in a CT image.

By using the CT images obtained by subtracting two CT images acquired under the same conditions and slice locations, we have devised a method for detecting streak artifacts in non-uniform regions and only radiological noise components in CT images. A chest phantom was scanned using 16- and 64-multidetector row helical CT scanners with various mAs values at 120kVp. The upper lung slice image was employed as a target image for evaluating the streak artifacts and radiological noise. One hundred parallel line segments with a length of 80 pixels were placed on the subtracted CT image, and the largest CT value in each CT value profile was employed as a feature variable of the streak artifacts; these feature variables were analyzed with the extreme value theory (Gumbel distribution). To detect only the radiological noise, all CT values contained in the 100 line profile were plotted on normal probability paper and the standard deviation was estimated from the inclination of its fitted line for the CT value plots. The two detection methods devised in this study were able to evaluate the streak artifacts and radiological noise in the CT images with high accuracy.

Quantitative assessment of image noise and streak artifact on CT image: comparison of z-axis automatic tube current modulation technique with fixed tube current technique.

The purpose of our study is to quantitatively assess the effects of z-axis automatic tube current modulation technique on image noise and streak artifact, by comparing with fixed tube current technique. Standard deviation of CT-values was employed as a physical index for evaluating image noise, and streak artifact was quantitatively evaluated using our devised Gumbel evaluation method. z-Axis automatic tube current modulation technique will improve image noise and streak artifact, compared with fixed tube current technique, and will make it possible to significantly reduce radiation doses at lung levels while maintaining the same image quality as fixed tube current technique.