Z-score-based semi-quantitative analysis of the volume of the temporal horn of the lateral ventricle on brain CT images.

The volume of the temporal horn of the lateral ventricle (THLV) on brain computed tomography (CT) images is important for neurologic diagnosis. Our purpose in this study was to develop a z-score-based semi-quantitative analysis for estimation of the THLV volume by using voxel-based morphometry. The THLV volume was estimated by use of a z-score mapping method that consisted of four main steps: anatomic standardization, construction of a normal reference database, calculation of the z score, and calculation of the mean z score in a volume of interest (VOI). A mean z score of the CT value obtained from a VOI around the THLV was used as an index for the THLV volume. CT scans from 50 subjects were evaluated. For evaluation of the accuracy of this method for estimating the THLV volume, the THLV volume was determined manually by neuroradiologists (serving as the reference volume). A mean z score was calculated from the VOI for each THLV of the 50 subjects by use of the proposed method. The accuracy of this method was evaluated by use of the relationship between the mean z score and the reference volume. The quadratic polynomial regression equation demonstrated a statistically significant correlation between the mean z score and the reference volume of the THLV (R (2) = 0.94; P < 0.0001). In 92 of 100 THLVs (92 %), the 95 % prediction interval of the regional mean z score captured the reference volume of the THLV. The z-score-based semi-quantitative analysis has the potential quantitatively to estimate the THLV volume on CT images.

[Quality assessment of X-ray images using modulation transfer function fractal dimension].

Objective evaluation, e.g., using the modulation transfer function (MTF) or the noise power spectrum (NPS) of an X-ray imaging system may not correctly correspond to the subject's evaluation, e.g., when using the receiver operating characteristic (ROC). Moreover, it is difficult to measure MTF or NPS from clinical images. We therefore applied MTF fractal dimension to an X-ray imaging system. The MTF fractal dimension includes the frequency properties of the human eye in addition to quantitative complexity. In this study, we demonstrated a relationship between basic image quality and MTF fractal dimension using simulated and actual X-ray images.

[Detection method for blurred regions in radiographs].

In this paper, we propose a detection method for blurred regions in radiographs. The method involves edge detection using a Sobel filter, manually determining the region of interest (ROI), feature calculation, and classification using a support vector machine. We applied our method to 14 phantom images (7 normal images, 7 blurred images) and 14 clinical images (12 normal images, 2 blurred images). As a result, the average classification accuracies of ROIs with blurring and ROIs without blurring were 98% and 90% for phantom images and clinical images, respectively.

An automated detection method for the MCA dot sign of acute stroke in unenhanced CT.

The hyperdense middle cerebral artery (MCA) dot sign representing a thromboembolus is one of the important computed tomography (CT) findings for acute stroke on unenhanced CT images. Our purpose in this study was to develop an automated method for detection of the MCA dot sign of acute stroke on unenhanced CT images. The algorithm of the method which we developed consisted of 5 major steps: extraction of the sylvian fissure region, initial identification of MCA dots based on the morphologic top-hat transformation, feature extraction of candidates, elimination of false positives (FPs) by use of a rule-based scheme, and classification of candidates using a support vector machine (SVM) classifier with four features. Our database comprised 297 CT images obtained from seven patients with the MCA dot sign. The performance of this scheme for classification of the MCA dot sign was evaluated by means of a leave-one-case out method. The performance of the classification by use of the SVM achieved a maximum sensitivity of 97.5% (39/40) at a FP rate of 1.28 per image. The sensitivity for detection of the MCA dot sign was 97.5% (39/40) with a FP rate of 0.5 per hemisphere. The method we developed has the potential to detect the MCA dot sign of acute stroke on unenhanced CT images.

Comparison of a discrete wavelet transform method and a modified undecimated discrete wavelet transform method for denoising of mammograms.

The purpose of this study was to evaluate the performance of a conventional discrete wavelet transform (DWT) method and a modified undecimated discrete wavelet transform (M-UDWT) method applied to mammographic image denoising. Mutual information, mean square error, and signal to noise ratio were used as image quality measures of images processed by the two methods. We examined the performance of the two methods with visual perceptual evaluation. A two-tailed F test was used to measure statistical significance. The difference between the M-UDWT processed images and the conventional DWT-method processed images was statistically significant (P<0.01). The authors confirmed the superiority and effectiveness of the M-UDWT method. The results of this study suggest the M-UDWT method may provide better image quality as compared to the conventional DWT.

Improving image quality in medical images using a combined method of undecimated wavelet transform and wavelet coefficient mapping.

We propose a method for improving image quality in medical images by using a wavelet-based approach. The proposed method integrates two components: image denoising and image enhancement. In the first component, a modified undecimated discrete wavelet transform is used to eliminate the noise. In the second component, a wavelet coefficient mapping function is applied to enhance the contrast of denoised images obtained from the first component. This methodology can be used not only as a means for improving visual quality of medical images but also as a preprocessing module for computer-aided detection/diagnosis systems to improve the performance of screening and detecting regions of interest in images. To confirm its superiority over existing state-of-the-art methods, the proposed method is experimentally evaluated via 30 mammograms and 20 chest radiographs. It is demonstrated that the proposed method can further improve the image quality of mammograms and chest radiographs, as compared to two other methods in the literature. These results reveal the effectiveness and superiority of the proposed method.

A modified undecimated discrete wavelet transform based approach to mammographic image denoising.

In this work, the authors present an effective denoising method to attempt reducing the noise in mammographic images. The method is based on using hierarchical correlation of the coefficients of discrete stationary wavelet transforms. The features of the proposed technique include iterative use of undecimated multi-directional wavelet transforms at adjacent scales. To validate the proposed method, computer simulations were conducted, followed by its applications to clinical mammograms. Mutual information originating from information theory was used as an evaluation measure for selection of an optimal wavelet basis function. We examined the performance of the proposed method by comparing it with the conventional undecimated discrete wavelet transform (UDWT) method in terms of processing time-consuming and image quality. Our results showed that with the use of the proposed method the computation time can be reduced to approximately 1/10 of the conventional UDWT method consumed. The results of visual assessment indicated that the images processed with the proposed UDWT method showed statistically significant superior image quality over those processed with the conventional UDWT method. Our research results demonstrate the superiority and effectiveness of the proposed approach.

Measurement of muscle activities for evaluating physical burden and pain during mammography positioning.

Mammography has become widespread as a standard method for breast cancer screening. For women undergoing mammography, compression of the breast and special positioning are requested, and they cause the physical burden and pain. However, the reality of the physical burden and subjective pain associated with mammography are not fully understood. We therefore measured the muscle activity of subjects during positioning for mammography screening using surface electromyography to evaluate the physical burden and pain associated with the positioning. The subjects consisted of 15 women (age: 44.4 ± 6.56 years old, height: 160 ± 6.7 cm, weight: 55.08 ± 3.94 kg, and body mass index: 21.4 ± 2.21). Measurements were performed in the mediolateral oblique position, a standard position for mammography. The target muscles were the sternocleidomastoid, biceps, trapezius and gastrocnemius muscles. A portable multi-purpose bio-amplifier was used for the measurements. Visual analogue scale (VAS), which is a tool for self-assessment of subjective pain, was used for pain measurement. The analysis of variance showed the significant difference in the amounts of muscle activities in all the target muscles between the relaxation phase before mammography positioning and the stress phase during mammography positioning. The sites with the increased muscle activities were consistent with the sites of pain measured with the VAS. These results suggest that positioning during mammography affects the muscle activity and that the increased muscle activity could be related to the pain. Understanding muscle activities during mammography is invaluable in making the pain reduction program for the subjects undergoing mammography.

Computerized detection of lung nodules by CT for radiologic technologists in preliminary screening.

In Japan, radiologists and radiologic technologists are endeavoring to improve the quality of lung CT screening. In particular, preliminary screening by radiologic technologists is expected to decrease radiologists' burden and improve the accuracy of CT screening. We considered that an application of computer-aided detection (CAD) would also be as useful in preliminary screening as in the radiologist's regular reading. Our purpose in this study was to investigate the potential of the application of CAD to preliminary screening. CAD software that we developed was applied to 17 lung CT scans that radiologic technologists had pre-interpreted. A radiologist recognized 29 lung nodules from the CT images, whereas radiologic technologists did not recognize 11 of the 29 nodules at their pre-reading. Our CAD software detected lung nodules at an accuracy of 100% (29/29), with 4.1 false positives per case. The 11 nodules that radiologic technologists did not recognize were included in the CAD-detected nodules. This result suggests that the application of CAD may aid radiologic technologists in their preliminary screening.

Computer-aided detection scheme for identification of hypoattenuation of acute stroke in unenhanced CT.

Our purpose in this study was to develop a computer-aided detection scheme for identification of hypoattenuation of acute stroke on unenhanced CT images to select patients for thrombolysis of acute stroke. This method is based on a z-score mapping method. The algorithm of the developed method consisted of five main steps: anatomic standardization, calculation of the z-score with a normal reference database, extraction of candidate voxels for hypoattenuation, feature extraction, and classification. The territory of the middle cerebral artery was divided into ten specified regions, according to a visually quantitative CT scoring system, the Alberta Stroke Programme Early CT Score (ASPECTS) method. Each of the ASPECTS-defined regions was classified as hypoattenuation or normality by linear discriminate analysis. The method was applied to 26 patients who had hypoattenuation areas (<6 h). The performance of this scheme for classification of hypoattenuation was evaluated using a leave-one-case-out method. As a result, an average sensitivity of 89.7% and an average specificity of 85.2% for automatically classifying hypoattenuation regions in the lentiform nucleus and the insular regions were obtained, and the average accuracy for the classification of hypoattenuation per patient was 84.6% (range 55.6-100%). The newly developed method has the potential accurately to identify hypoattenuation of acute stroke in the ASPECTS-defined regions.

[A preliminary study on measurement of muscle activity during mammography positioning].

This study focused on measuring examinees' muscle activities during mammography positioning using surface electromyography. Muscle activities were measured in three women (40-50s) in two-view mammography (MLO: mediolateral oblique, CC: craniocaudal). The muscles measured were the sternocleidomastoid, biceps, trapezius, and gastrocnemius, selected based on the visual analogue scale reported by Sharp et al. We used a multi-purpose portable bio-amplifier (Polymate AP1000) to assess the muscle activities. The results showed that the trapezius in right MLO and sternocleidomastoid in right CC were active in all three subjects. This suggests that the muscles directly related to mammography positioning are highly active. In addition, the gastrocnemius was active throughout the mammography. The biceps and gastrocnemius were also active in at least one of the three women. We believe that quantitative assessment of muscle activities during mammography positioning will contribute to the improvement of pain-reduction programs in mammography.

Usefulness of z-score mapping for quantification of extent of hypoattenuation regions of hyperacute stroke in unenhanced computed tomography: analysis of radiologists' performance.

OBJECTIVE: The purpose of this study was to evaluate the usefulness of z-score mapping method on neuroradiologists' performance in quantification of the extent of hypoattenuation regions of hyperacute stroke on unenhanced computed tomographic (CT) images by using the Alberta Stroke Programme Early CT Score system. METHODS: Twenty-one patients with infarction (<3 hours) were retrospectively selected. Five neuroradiologists interpreted CT images first without and then with z-score maps by using the Alberta Stroke Programme Early CT Score system. Their performances in the quantification of the extent of hypoattenuation were compared. RESULTS: Average accuracies for the quantification without and with the z-score maps were 82.6% and 86.6%, respectively (P < 0.0001). The average area under the receiver operating characteristic curve for detection of focal hypoattenuation significantly increased from 0.883 to 0.925 (P = 0.01) by use of z-score maps. CONCLUSIONS: The use of z-score mapping method has the potential to help neuroradiologists quantify the extent of hypoattenuation regions of hyperacute stroke on unenhanced CT images.

Z-score mapping method for extracting hypoattenuation areas of hyperacute stroke in unenhanced CT.

RATIONALE AND OBJECTIVES: The purpose of this study was to develop a z-score mapping method on the basis of a voxel-by-voxel analysis to visualize hypoattenuation areas of hyperacute stroke on unenhanced computed tomographic (CT) images. MATERIALS AND METHODS: The algorithm of the developed method consisted of five main steps: anatomic standardization, the construction of a normal reference database, calculation of the z scores, the elimination of false-positive areas, and the extraction of hypoattenuation areas. The obtained z-score map was then superimposed on the original CT images for identifying hypoattenuation areas of hyperacute stroke on the unenhanced CT images. The method was applied to 21 patients with infarctions of the middle cerebral artery territory <3 hours after symptom onset. The performance of the method was evaluated using receiver-operating characteristic analysis. RESULTS: Hypoattenuation regions could be significantly distinguished from normal regions by z-score values (P < .0001). The area under the receiver-operating characteristic curve for distinction between 68 hypoattenuation regions and 142 normal regions was 0.834. CONCLUSIONS: The developed method has the potential to accurately indicate high-signal intensity areas corresponding to hypoattenuation areas on CT images in the hyperacute stage of stroke.

Computerized quantitative evaluation of mammographic accreditation phantom images.

PURPOSE: The objective was to develop and investigate an automated scoring scheme of the American College of Radiology (ACR) mammographic accreditation phantom (RMI 156, Middleton, WI) images. METHODS: The developed method consisted of background subtraction, determination of region of interest, classification of fiber and mass objects by Mahalanobis distance, detection of specks by template matching, and rule-based scoring. Fifty-one phantom images were collected from 51 facilities for this study (one facility provided one image). A medical physicist and two radiologic technologists also scored the images. The human and computerized scores were compared. RESULTS: In terms of meeting the ACR's criteria, the accuracies of the developed method for computerized evaluation of fiber, mass, and speck were 90%, 80%, and 98%, respectively. Contingency table analysis revealed significant association between observer and computer scores for microcalcifications (p<5%) but not for masses and fibers. CONCLUSIONS: The developed method may achieve a stable assessment of visibility for test objects in mammographic accreditation phantom image in whether the phantom image meets the ACR's criteria in the evaluation test, although there is room left for improvement in the approach for fiber and mass objects.

Improvement of determination technique for extracting centerline in coronary artery with calcification on CTA.

The present study proposes a method for improving an existing technique used for extracting the centerlines of coronary arteries with calcifications on CTA. Through the use of the improved centerline extraction method, CPR images could be depicted accurately. In the proposed method, two dynamic range compression algorithms using two ITC for blood vessel regions and calcification regions were employed. Two dynamic range compressed CTA images obtained from the two ITC were then subtracted. After that, automatic tracing to determine the centerline for creating CPR images was performed using 3D image processing equipment. The usefulness of our proposed method was confirmed by using simulated CTA of the coronary artery with calcification. We also applied the proposed method to CTA images of 39 branches in 18 cases, and to 48 segments. Our experimental results showed that automatic tracing software pre-installed in the workstation could accurately determine the centerline of the coronary artery without being affected by the existence of calcification. Furthermore, an experienced radiological technologist evaluated the CPR images obtained by the proposed method. The results showed that most created CPR images could be used as diagnostic images after a minor revision performed manually.

[Evaluation of irreversible compressed images in computed radiography using physical image quality measures].

Joint photographic experts group(JPEG)and JPEG2000 are widely used as image compression algorithms in medical image database systems. Compressed images have been mainly evaluated by visual assessment on acceptable compression levels in clinical studies. However, to the best of our knowledge, little work has been done to clarify image properties based on physical analysis. In this work, investigations were made to clarify image properties based on physical analysis and to discuss the major causes of degradation related to compression ratios. The physical properties of JPEG2000-compressed and JPEG-compressed images in computed radiography(CR)were compared by measuring the characteristic curve, modulation transfer function(MTF), noise power spectrum(NPS), peak signal-to-noise ratio(PSNR), contrast-to-noise ratio(CNR), and noise equivalent quanta(NEQ). In the MTF measurement, the MTFs of JPEG at high compression ratio showed pronounced degradation at all frequencies. The NPS values of JPEG2000 tend to decrease considerably compared to that of the JPEG at all frequencies with the increase of compression ratio. Furthermore, JPEG2000 images showed higher PSNR, CNR, and NEQ values than JPEG images in the same compression ratio. In these signal-to-noise ratio measurements, good reproducibility of JPEG2000 images was achieved. Overall, JPEG2000 compressed images were far superior to JPEG compressed images. In the physical properties measured, these physical analyses are useful to comprehend physical properties for each irreversible compressed image related to compression ratios in CR.

[Improvement of detection of early CT signs in hyperacute stroke using a novel noise reduction filter].

PURPOSE: In the diagnosis of hyperacute stroke, an early CT sign such as the loss of gray-white matter interface may be difficult to detect within the first hours of the onset of symptoms because of the presence of quantum noise on CT images. We present a method for improving the detection of early CT sign, and to evaluate whether our method can help radiologists detect the early CT signs at emergency CT scan. METHODS AND MATERIALS: Our method provides an adaptive partial median filter (APMF), which can reduce local noise without blurring of anatomical structure using variable filter shape and size according to the pixel value distribution of object around a center pixel. The APMF can enhance the loss of gray-white matter interface due to hyperacute stroke. Twenty-six patients with early CT signs at the lentiform nucleus and/or the cortical ribbon and 49 control subjects were included in an observer study. The CT images of 26 patients with acute (<5 hours) middle cerebral artery territory infarction were proved with follow-up CT. The APMF was applied to all the CT images. Four radiologists, without and with applying the APMF, indicated their confidence level regarding the presence (or absence) of the early CT signs on each CT images. Receiver operating characteristic (ROC) curves were calculated to evaluate the observers' performance. RESULTS: A 78% noise reduction with the APMF was obtained from simulation. The average area under the ROC curve (Az) was improved from 0.868 to 0.924 for all radiologists by applying the APMF to the original images. The difference in Az values with and without the APMF was statistically significant with a P value of .002 for all radiologists. CONCLUSION: Our proposed APMF can improve the visibility of gray-white matter interface. As a result, the APMF can help radiologists detect the early CT signs at emergency CT scan.

Information entropy measure for evaluation of image quality.

This paper presents a simple and straightforward method for synthetically evaluating digital radiographic images by a single parameter in terms of transmitted information (TI). The features of our proposed method are (1) simplicity of computation, (2) simplicity of experimentation, and (3) combined assessment of image noise and resolution (blur). Two acrylic step wedges with 0-1-2-3-4-5 and 0-2-4-6-8-10 mm in thickness were used as phantoms for experiments. In the present study, three experiments were conducted. First, to investigate the relation between the value of TI and image noise, various radiation doses by changing exposure time were employed. Second, we examined the relation between the value of TI and image blurring by shifting the phantoms away from the center of the X-ray beam area toward the cathode end when imaging was performed. Third, we analyzed the combined effect of deteriorated blur and noise on the images by employing three smoothing filters. Experimental results show that the amount of TI is closely related to both image noise and image blurring. The results demonstrate the usefulness of our method for evaluation of physical image quality in medical imaging.

[Development of an algorithm for the detection of early signs of cerebral ischemia on CT images].

This paper describes an approach to automatically detect the parenchymal hypoattenuation of hyperacute stroke in nonenhanced computed tomography (CT) images. This technique is based on a comparison between the CT values histograms of right and left brains. A subtraction curve that was regarded as an output value was calculated by subtracting the right-hemispherical histogram from the left-hemispherical histogram obtained from one of the region-of-interest (ROI) sets on an image. The output value was used to assess whether hypoattenuation exists on CT images with a threshold value. If judged abnormal, a rectangular region including a whole or partial hypoattenuation area was detected from the ROI. Twenty-six cases with hypoattenuation and 30 cases without hypoattenuation were included in this study. As a result of our experiments, the sensitivity of this method in detecting hypoattenuation was found to be 92%, with approximately 0.16 false-positive per image. Our preliminary experimental results indicated that the proposed technique can be used for the automated detection of parenchymal hypoattenuation of hyperacute stroke on nonenhanced CT images.

Novel noise reduction filter for improving visibility of early computed tomography signs of hyperacute stroke: evaluation of the filter's performance--preliminary clinical experience.

PURPOSE: The aim of this study was to evaluate the performance of a novel noise reduction filter for improving the visibility of early computed tomography (CT) signs of hyperacute stroke on nonenhanced CT images. MATERIAL AND METHODS: Fourteen patients with a middle cerebral artery occlusion within 4.5 h after onset were evaluated. The signal-to-noise ratio (SNR) of the processed images with the noise reduction filter and that of original images were measured. Two neuroradiologists visually rated all the processed and original images on the visibility of normal and abnormal gray-white matter interfaces. RESULTS: The SNR value of the processed images was approximately eight times as high as that of the original images, and a 87% reduction of noise was achieved using this technique. For the visual assessment, the results showed that the visibility of normal gray-white matter interface and that of the loss of the gray-white matter interface were significantly improved using the proposed method (P < 0.05). CONCLUSION: The noise reduction filter proposed in the present study has the potential to improve the visibility of early CT signs of hyperacute stroke on nonenhanced CT images.