Quantitative assessment of image quality enhancement due to unsharp-mask processing in x-ray fluoroscopy

Edge enhancement algorithm for low-dose X-ray fluoroscopic imaging

BACKGROUND AND OBJECTIVE

Low-dose X-ray fluoroscopy has continually evolved to reduce radiation risk to patients during clinical diagnosis and surgery. However, the reduction in dose exposure causes quality degradation of the acquired images. In general, an X-ray device has a time-average pre-processor to remove the generated quantum noise. However, this pre-processor causes blurring and artifacts within the moving edge regions, and noise remains in the image. During high-pass filtering (HPF) to enhance edge detail, this noise in the image is amplified.

METHODS

In this study, a 2D edge enhancement algorithm comprising region adaptive HPF with the transient improvement (TI) method, as well as artifacts and noise reduction (ANR), was developed for degraded X-ray fluoroscopic images. The proposed method was applied in a static scene pre-processed by a low-dose X-ray fluoroscopy device. First, the sharpness of the X-ray image was improved using region adaptive HPF with the TI method, which facilitates sharpening of edge details without overshoot problems. Then, an ANR filter that uses an edge directional kernel was developed to remove the artifacts and noise that can occur during sharpening, while preserving edge details.

RESULTS

The quantitative and qualitative results obtained by applying the developed method to low-dose X-ray fluoroscopic images and visually and numerically comparing the final images with images improved using conventional edge enhancement techniques indicate that the proposed method outperforms existing edge enhancement methods in terms of objective criteria and subjective visual perception of the actual X-ray fluoroscopic image.

CONCLUSIONS

The developed edge enhancement algorithm performed well when applied to actual low-dose X-ray fluoroscopic images, not only by improving the sharpness, but also by removing artifacts and noise, including overshoot.

Innovative algorithm to evaluate the capabilities of visual, near infrared, and infrared technologies for the detection of veins for intravenous cannulation

Intravenous cannulation is the process of inserting a cannula into a vein to administrate medication, fluids, or to take blood samples. The process of identification and of locating veins plays an important role during the intravenous cannulation procedure to reduce health care costs and the suffering of patients. This paper compares the three technologies used to assess their suitability and capability for the detection of veins to support the cannulation process. Three types of cameras are used in this study; a visual, an infrared, and a near infrared. The collected images, 103 in total, from the three technologies have been analyzed using a wide range of image processing techniques and compared with identification templates to evaluate the performance of each technology. The results show that the near infrared technology supported by suitable LED illumination is the most effective for the visualization of veins. However, infrared thermography is found to be successful when followed by a cold stimulation.

A spatio-temporal detective quantum efficiency and its application to fluoroscopic systems

PURPOSE

Fluoroscopic x-ray imaging systems are used extensively in spatio-temporal detection tasks and require a spatio-temporal description of system performance. No accepted metric exists that describes spatio-temporal fluoroscopic performance. The detective quantum efficiency (DQE) is a metric widely used in radiography to quantify system performance and as a surrogate measure of patient "dose efficiency". It has been applied previously to fluoroscopic systems with the introduction of a temporal correction factor. However, the use of a temporally-corrected DQE does not provide system temporal information and it is only valid under specific conditions, many of which are not likely to be satisfied by suboptimal systems. The authors propose a spatio-temporal DQE that describes performance in both space and time and is applicable to all spatio-temporal quantum-based imaging systems.

METHODS

The authors define a spatio-temporal DQE (two spatial-frequency axes and one temporal-frequency axis) in terms of a small-signal spatio-temporal modulation transfer function (MTF) and spatio-temporal noise power spectrum (NPS). Measurements were made on an x-ray image intensifier-based bench-top system using continuous fluoroscopy with an RQA-5 beam at 3.9 microR/frame and hardened 50 kVp beam (0.8 mm Cu filtration added) at 1.9 microR/frame.

RESULTS

A zero-frequency DQE value of 0.64 was measured under both conditions. Nonideal performance was noted at both larger spatial and temporal frequencies; DQE values decreased by approximately 50% at the cutoff temporal frequency of 15 Hz.

CONCLUSIONS

The spatio-temporal DQE enables measurements of decreased temporal system performance at larger temporal frequencies analogous to previous measurements of decreased (spatial) performance. This marks the first time that system performance and dose efficiency in both space and time have been measured on a fluoroscopic system using DQE and is the first step toward the generalized use of DQE on clinical fluoroscopic systems.

[An investigation of the subjective assessment of fluoroscopic imaging using instantaneous detectability]

Instantaneous detectability was introduced in a method for the subjective assessment of fluoroscopic images, particularly in the interventional radiology (IVR) procedure. Quantitatively, instantaneous detectability was obtained by measuring the time required for observers to detect the tip of a linear pattern, such as a guide wire, just after the image is displayed. Dynamic images used in this measurement, which mimic degraded fluoroscopic images, were created in the computer simulation software by adding a low-contrast linear pattern to a noisy background image. Radiological technologists and students in the faculty of computer engineering participated in the assessment, and all measurements were performed using a personal computer system. Even if the contrast-to-noise ratio was identical, instantaneous detectability was remarkably increased when the background noise was dominated by higher frequency components. Also, the sign test suggested that a frame rate of 30 f/s significantly improved detectability compared to a frame rate of 15 f/s. These results enable us to discuss new possibilities for image processing and the optimization of system performance. Although the standard deviation of the measured inter- and intra-observer data was large, statistical significance should be suitably examined by a paired-comparison like the sign test, which will be one of the important analyzers in experiments investigating human performance.

Visualization of color anatomy and molecular fluorescence in whole-mouse cryo-imaging

We developed multi-scale, live-time interactive visualization of color image data, including microscopic whole-mouse cryo-images serving many biomedical applications. Using true-color volume rendering, we interactively, selectively enhanced anatomy using feature detection. For example, to enhance red organs (vessels, liver, etc.) and internal surfaces, we computed a red feature from R/(R+G+B) and surface features from color/gray-scale gradients, respectively. For >70GB cryo-image volumes, we developed multi-resolution visualization, which provided low-resolution rendering of an entire mouse and zooming to organs, tissues, and cells. Fusions of fluorescence and color cryo-volumes uniquely showed biodistribution of metastatic and stem cells within an anatomical context.

Adaptive enhancement of sea-surface targets in infrared images based on local frequency cues

Image enhancement is an important preprocessing step of infrared (IR) based target recognition and surveillance systems. For a better visualization of targets, it is vital to develop image enhancement techniques that increase the contrast between the target and background and emphasize the regions in the target while suppressing noises and background clutter. This study proposes what we believe to be a novel IR image enhancement method for sea-surface targets based on local frequency cues. The image is transformed blockwise into the Fourier domain, and clustering is done according to the number of expected regions to be enhanced in the scene. Based on the variations in the elements in any cluster and the differences between the cluster centers in the frequency domain, two gain matrices are computed for midfrequency and high frequency images by which the image is enhanced accordingly. We provide results for real data and compare the performance of the proposed algorithm through subjective and quantitative tests with four different enhancement methods. The algorithm shows a better performance in the detail visibility of the target.

A small-signal approach to temporal modulation transfer functions with exposure-rate dependence and its application to fluoroscopic detective quantum efficiency

The detective quantum efficiency (DQE) is a metric widely used in radiography to quantify system performance and as a surrogate measure of patient "dose efficiency." It has been applied previously to fluoroscopic systems with the introduction of a temporal correction factor. Calculation of this correction factor relies on measurements of the temporal modulation transfer function (MTF). However, the temporal MTF is often exposure-rate dependent, violating a necessary Fourier linearity requirement. The authors show that a Fourier analysis is appropriate for fluoroscopic systems if a "small-signal" approach is used. Using a semitransparent edge, a lag-corrected DQE is described and measured for an x-ray image intensifier-based fluoroscopic system under continuous (non-pulsed) exposure conditions. It was found that results were equivalent for both rising and falling-edge profiles independent of edge attenuation when effective attenuation was in the range of 0.1-0.6. This suggests that this range is appropriate for measuring the small-signal temporal MTF. In general, lag was greatest at low exposure rates. It was also found that results obtained using a falling-edge profile with a radiopaque edge were equivalent to the small-signal results for the test system. If this result is found to be true generally, it removes the need for the small-signal approach. Lag-corrected DQE values were validated by comparison with radiographic DQE values obtained using very long exposures under the same conditions. Lag was observed to inflate DQE measurements by up to 50% when ignored.

A moving slanted-edge method to measure the temporal modulation transfer function of fluoroscopic systems

Lag in fluoroscopic systems introduces a frame-averaging effect that reduces measurements of image noise and incorrectly inflates measurements of the detective quantum efficiency (DQE). A correction can be implemented based on measurements of the temporal modulation transfer function (MTF). We introduce a method of measuring the temporal MTF under fluoroscopic conditions using a moving slanted edge, a generalization of the slanted-edge method used to measure the (spatial) MTF, providing the temporal MTF of the entire imaging system. The method uses a single x-ray exposure, constant edge velocity, and assumes spatial and temporal blurring are separable. The method was validated on a laboratory x-ray image intensifier (XRII) system by comparison with direct measurements of the XRII optical response, showing excellent agreement over the entire frequency range tested (+/- 100 Hz). With proper access to linearized data and continuous fluoroscopy, this method can be implemented in a clinical setting on both XRII and flat-panel detectors. It is shown that the temporal MTF of the CsI-based validation system is a function of exposure rate. The rising-edge response showed more lag than the falling edge, and the temporal MTF decreased with decreasing exposure rate. It is suggested that a small-signal approach, in which the range of exposure rates is restricted to a linear range by using a semitransparent moving edge, would be appropriate for measuring the DQE of these systems.

Multifunctional nanocarriers for mammographic quantification of tumor dosing and prognosis of breast cancer therapy

Nanoscale therapeutic interventions are increasingly important elements in the portfolio of cancer therapeutics. The efficacy of nanotherapeutics is dictated, in part, by the access they have to tumors via the leaky tumor vasculature. Yet, the extent of tumor vessel leakiness in individual tumors varies widely resulting in a correspondingly wide tumor dosing and resulting range of responses to therapy. Here we report the design of a multifunctional nanocarrier that simultaneously encapsulates a chemotherapeutic and a contrast agent which enables a personalized nanotherapeutic approach for breast cancer therapy by permitting tracking of the nanocarrier distribution by mammography, a widely used imaging modality. Following systemic administration in a rat breast tumor model, imaging demonstrated a wide range of intratumoral deposition of the nanocarriers, indicating variable tumor vessel leakiness. Notably, specific tumors that exhibited high uptake of the nanocarrier as visualized by imaging were precisely the animals that responded best to the treatment as quantified by low tumor growth and prolonged survival.

Quantitative image quality evaluation of pixel-binning in a flat-panel detector for x-ray fluoroscopy

X-ray fluoroscopy places stringent design requirements on new flat-panel (FP) detectors, requiring both low-noise electronics and high data transfer rates. Pixel-binning, wherein data from more that one detector pixel are collected simultaneously, not only lowers the data transfer rate but also increases x-ray counts and pixel signal-to-noise ratio (SNR). In this study, we quantitatively assessed image quality of image sequences from four acquisition methods; no-binning and three types of binning; in synthetic images using a clinically relevant task of detecting an extended guidewire in a four-alternative forced-choice paradigm. Binning methods were conventional data-line (D) and gate-line (G) binning, and a novel method in which alternate frames in an image sequence used D and G binning. Two detector orientations placed the data lines either parallel or perpendicular to the guide wire. At a low exposure of 0.6 microR (1.548 x 10(-10) C/kg) per frame, irrespective of detector orientation, D binning with its reduced electronic noise was significantly (p<0.1) better than the other acquisition methods. On average, alternate binning performed better than G binning. At a higher exposure of 4.0 microR (10.32 x 10(-10) C/kg) per frame, with data lines parallel to the guidewire, detection with D binning was significantly (p<0.1) better than G binning. However, with data lines perpendicular to the guidewire, G binning was significantly (p<0.1) better than D binning because the partial area effect was reduced. Alternate binning was the best binning method when results were averaged over both orientations, and it was as good as the best binning method at either orientation. In addition, at low and high exposures, alternate binning gave a temporally fused image with a smooth guidewire, an important image quality feature not assessed in a detection experiment. While at high exposure, detection with no binning was as good, or better, than the best binning method, it might be impractical at fluoroscopy imaging rates. A computational observer model based on signal detection theory successfully fit data and was used to predict effects of similar acquisition methods. Results from this study suggest the use of exposure-dependent detector binning in fluoroscopy that switches between D binning and alternate binning at low and high exposures, respectively.