Michael J. Flynn

A method for measuring the presampled MTF of digital radiographic systems using an edge test device

The modulation transfer function (MTF) of radiographic systems is frequently evaluated by measuring the systems line spread function (LSF) using narrow slits. The slit method requires precise fabrication and alignment of a slit and high radiation exposure. An alternative method for determining the MTF uses a sharp, attenuating edge device. We have constructed an edge device from a 250-microm-thick lead foil laminated between two thin slabs of acrylic. The device is placed near the detector and aligned with the aid of a laser beam and a holder such that a polished edge is parallel to the x-ray beam. A digital image of the edge is processed to obtain the presampled MTF. The image processing includes automated determination of the edge angle, reprojection, sub-binning, smoothing of the edge spread function (ESF), and spectral estimation. This edge method has been compared to the slit method using measurements on standard and high-resolution imaging plates of a digital storage phosphor (DSP) radiography system. The experimental results for both methods agree with a mean MTF difference of 0.008. The edge method provides a convenient measurement of the presampled MTF for digital radiographic systems with good response at low frequencies.

Experimental comparison of noise and resolution for 2k and 4k storage phosphor radiography systems.

The purpose of this study was to compare the image quality for a digital storage phosphor system using 1760 x 2140 (2k) and 3520 x 4280 (4k) image arrays. Measurements were made on a chest radiography system (Fuji FCR-9501) with special provisions to be operated in both 2k (standard) and 4k (HQ) modes. Presampled modulation transfer functions (MTF) were measured using an edge method. Noise power spectra (NPS) were determined for different input exposures by two-dimensional Fourier analysis. These measures along with exposure measurements and an x-ray spectral model were used to determine the frequency-dependent detective quantum efficiency DQE (f) of the system for the 4k and the 2k modes. The magnitude of the NPS for the 4k mode was about 1/2 that of the 2k mode. A MTF value of 0.5 was found at 1.25 cycles/mm for the 4k system and 1.50 cycles/mm for the 2k system. The 4k images had an extended MTF of 0.1 at 4.5 cycles/mm in the plate-scan direction. Overall, the DQE (f) of the 4k mode was slightly better than that for the 2k mode by about 0.02 due primarily to its better noise characteristics.

Microfocus X-ray sources for 3D microtomography

Abstract An analytic model for the performance of cone beam microtomography is described. The maximum power of a microfocus X-ray source is assumed to be approximately proportional to the focal spot size. Radiation flux penetrating the specimen is predicted by a semi-empirical relation which is valid for X-ray energies less than 20 keV. Good signal to noise ratio is predicted for bone specimens of 0.1 to 10 mm when scanned at the optimal energy. A flux of about 1 × 10 10 photons/mm 2 /s is identified for 0.2 mm specimens. Cone beam volumetric microtomography is found to compare favorably with synchrotron based methods.

A technique for measuring regional bone mineral density in human lumbar vertebral bodies

A method for measuring the regional bone mineral density (rBMD) in human lumbar vertebral bodies using a series of contiguous computed tomography images, each 1 mm thick, is fully described. The technique has a sample volume of 0.004 cm3, a sample spacing of 0.8 X 0.8 X 1.0 mm, and results in a bone marrow radiation dose of 1.59 to 2.75 rads (0.016-0.028 Gy). The use of physical density (mg/cm3) is introduced and the measurement noise (0.7-1.3%), accuracy (2.7%), and serial precision (0.2%) have been evaluated in vitro using appropriate phantoms. The corresponding percentage errors for accuracy and precision relative to K2HPO4 concentration were 6.9% and 2.0%, respectively. A multiple region density measurement is described and evaluated.

Trabecular microstructure and surface changes in the greater tuberosity in rotator cuff tears

Abstractn Objective. When planning surgery in patients with rotator cuff tear, strength of bone at the tendon insertion and trabecular bone structure in the greater tuberosity are usually taken into consideration. We investigated radiographic changes in bone structure of the greater tuberosity in rotator cuff tears.n Design. Twenty-two human cadaveric shoulders from subjects ranging from 55 to 75 years of age were obtained. The integrity of the rotator cuff was examined by sonography to determine if it is intact without any tear, or torn partially or completely. The humeral head was sectioned in 3xa0mm thick coronal slab sections and microradiographed. After digitization of the microradiographs and imaging processing with in-house semi-automated image processing software tools developed using software interfaces on a Sun workstation, the trabecular histomorphometrical structural parameters and connectivity in the greater tuberosity were quantified. The degenerative changes on the surface of the greater tuberosity were interpreted blindly by 2 independent readers.n Results. Among the 22 shoulder specimens, the rotator cuff was found intact in 10 shoulders, partially in 7 and fully torn in 5. Statistically significant loss in apparent trabecular bone volume fraction, number of trabecular nodes, and number of trabecular branches, and a statistically significant increase in apparent trabecular separation and number of trabecular free ends were found in the greater tuberosity of the shoulders with tears. The loss was greater in association with full tear than in partial tear. Thickening of the cortical margin of the enthesis, irregularity of its surface, and calcification beyond the tidemark were observed in 2 (20%) shoulders with intact rotator cuff, in 6 (86%) shoulders with partial tear, and in 5 (100%) shoulders with full tear.n Conclusions. Rotator cuff tears are associated with degenerative changes on the bone surface and with disuse osteopenia of the greater tuberosity. Aging, degenerative enthesopathy of the supraspinatus tendon, and rotator cuff tears appear closely related.

Method for measuring veiling glare in high-performance display devices

An experimental method for measuring the veiling glare characteristics of display devices is presented. The measured veiling glare ratio (G) is taken to be the luminance in the surrounding bright field divided by the luminance in a dark circle. The method is based on a collimated conic probe that minimizes signal contamination from bright surroundings allowing for measurements of low luminance in a circular dark spot of a test pattern. A correction factor computed with test patterns having opaque spots is introduced. The factor is expressed as a bivariate function of the dark-spot radius and the distance between the probe and the emissive surface. We studied the uncertainty introduced by the method by measuring veiling glare test patterns printed on radiographic film for which the transmission of the dark spots was determined experimentally. Performance characterization measurements show that signal contamination is less than 10(-4) of the bright field surrounding a dark circle. Our results show that G of a few hundred can be measured with an uncertainty of a few percent, and ratios of approximately 10(3) can be reported within 10%. Finally, we demonstrate the method by measuring G for a high-performance monochrome cathode-ray tube display.

Differentiation between benign and malignant disease of the breast using digital subtraction angiography of the breast

The authors have investigated digital subtraction angiography (DSA) for the differential diagnosis of breast lesions detected initially by mammography. Eighteen patients scheduled for biopsy first underwent digital subtraction angiography of the breast (DSAB). Criteria for malignancy included the presence of abnormal vessels and a “blush” in the area of the lesion. A total of 17 lesions are currently available for histopathologic correlation. Although this is a small series, the initial results of DSAB suggest its potential utility for differentiating between benign and malignant lesions.

Automated distortion correction of X-ray image intensifier images

An automated procedure for accurately correcting the distortion present in X-ray image intensifiers is described. An image of a rectilinear grid of wires is acquired. The wire crossing point positions are determined to sub-pixel accuracy without operator intervention. The points are then associated with their true coordinates. Following this association procedure, a piecewise affine transformation is found. Each output pixel point needed is mapped to the corresponding location in the distorted image. If it is not at a true acquired pixel location, bilinear interpolation is done to estimate the gray level at that point. After calibration data are analyzed, all subsequent images are corrected using a fast and simple table lookup algorithm. High accuracy is achieved for applications requiring sub-pixel registration.<<ETX>>

Technical innovation: digital tomosynthesis of the hip following intra-articular administration of contrast

ObjectiveTo demonstrate the clinical use of digital tomosynthesis in the depiction of labral and chondral pathology in the setting of post-operative CAM-type impingement of the hip following intra-articular administration of dilute iodinated contrast.Materials and MethodsWe present images from a 46xa0year-old African American female with suspected CAM-type femoroacetabular impingement (FAI) following percutaneous pinning of the right hip for slipped capital femoral epiphysis (SCFE).ResultsA partial tear of the labrum and clinically significant acetabular chondral abnormalities were demonstrated with the use of digital tomosynthesis with superb anatomic detail.ConclusionDigital tomosynthesis can be of great clinical utility and can depict pathology in superb anatomic detail, particularly in situations in which MRI is not available as well as under circumstances in which artifact due to orthopedic hardware is of concern as shown in this case.

Comparison of dual photon and dual energy X-ray bone densitometers in a clinic setting

In clinical practice, decisions must be made about whether and how to convert to newer technologies. To address this issue, two separate studies were conducted. We evaluated the relationships between results of lumbar spine measurements using two dual photon absorptiometry (DPA1 and DPA2) instruments and one dual energy X-ray (DXA) instrument with the same subjects (49 volunteers), and also in 65 patients who were measured on the DPA1 and DXA machines. Second, we measured the lumbar spine and the proximal femur in three groups of 12 female volunteers three times on one instrument within 1 week. We purposely simulated a busy clinic setting with different technologists, older radioactive sources, and a heterogeneous patient group. The comparison study indicated a significant difference between the mean bone density values reported by the machines, but the results were highly correlated (R2 = 0.89–0.96). The short-term precision errors (coefficients of variation) differed among the instruments, ranging from 1.3% (DXA of the spine) to 5.1% (DPA1 of the spine), and in the femoral neck, 2.3% and 2.4% (DXA and DPA1, respectively) versus 3.5% by DPA2. This study emphasizes the differences between instruments, the potential for greater error in busy clinic environments, and the apparent superiority of dual energy X-ray absorptiometry under these less than ideal conditions.