Modulation transfer function MTF

The detectability of critical defects with CT depends on the final image quality and the skill of the operator, see figure 2. The basic concepts of image quality are resolution, contrast, and noise. Image quality are generally described by the signal-to-noise ratio SNR), the modulation transfer function (MTF) and the noise power spectrum (NFS). SNR is the quotient of a signal and its variance, MTF describes the contrast as a function of spatial frequency and NFS in turn describes the noise power at various spatial frequencies [1, 3]. 

Modulation Transfer Function MTF The course of the MTF is calculated from the established inherent unsharpness. 

The unsharpness is generally measured with the duplex wire IQI (CERL B), strip pattern IQI-s (here we used a Siemens star) or adduced via the modulation transfer function (MTF). References [1,2,3] give the MTF s determined for the BAS2000, BAS2500 and BAS5000. 

Figure 2b. Profiles of the modulation transfer function (MTF), its inverse and Wiener inverse-filter.

Modulation transfer function (MTF) analyses, 19 222, 264-265 Module factor investment cost estimates, 9 530... 

Figure 2. Modulation Transfer Functions (MTF s) for the Perkin Elmer Micralign cameras operating at 250 nm, 300 nm and 400 nm, and for a step-and-repeat camera lens with a numerical aperture of 0.35.

The ultimate resolution that can be obtained with a Vidicon-tube system can best be seen from the manufacturers specification. The spatial resolution is expressed by the so called modulation-transfer function (MTF), which is measured by the projection of a test mask directly on the photocathode, with visible light. Of course, this test does not include the degradation by the phosphor screen in X-ray applications. 

Equal modulation transfer function (MTF) across the array. 

SIT ISIT. The resolution of SIT detectors can be defined in several ways— a) position (spatial) resolution, b) Rayleigh resolution, and c) modulation transfer function (MTF). 

Applying the superposition principle, the response to an initially sinusoidal modulation of the photoacid concentration, also called the modulation transfer function (MTF), can be calculated with Eq. (17.3) ... 

Spatial resolution can be characterized quantitatively and more usefully through the modulation transfer function (MTF). The MTF describes how well the imaging system or one of its components such as the detector transfers the contrast of sinusoidal patterns from the incident X-ray pattern to the output. A sinusoid is a repetitive function, characterized as having a frequency (in this case a spatial frequency specified in cydes/mm) and an amplitude. The concept of spatial frequency can be visualized by considering ripples in a pond. Low spatial frequencies (long distance between wave peaks) represent coarse structures and high spatial frequencies (short wavelengths) describe fine detail. 

As discussed in Chap. 1, digital images are acquired by sampling the pattern of X-rays transmitted by the breast. In practice, this is often accomplished using a detector that is constructed as an array of discrete detector elements or dels, each of which more or less independently measures the X-rays incident on it The pitch or spacing between dels and the dimensions of the active portion of each del (aperture) in part determine the spatial resolution properties of the imaging system. The concept of spatial resolution and its quantification in terms of the modulation transfer function (MTF) were introduced in Chap. 1. 

The EndoTester was designed and fabricated to perform a wide array of quantitative tests and measurements. Some of these tests include (1) Relative light loss, (2) Reflective symmetry, (3) Lighted (good) fibers, (4) Geometric distortion, and (5) Modulation transfer function (MTF). Each series of tests is associated with a specific endoscope to allow for trending and easy comparison of successive measurements. 

Figure 7. Modulation Transfer Function (MTF) measured with a CVD diamond window (lower curve), the MTF degradation caused by form shape errors (middle curve) and the MTF of the system with no window in place showing the diffraction limited case (upper curve).

Spatial resolution in imaging is a measure of how close two identical bright objects can be approximated before they can no longer be resolved due to vanishing image contrast (modulation) (Gonzalez and Woods 2002). The concept of modulation transfer function (MTF) can be used to describe spatial resolution mathematically. 

Fig. 6.5. Modulation transfer function (MTF) as a function of Ne where N is the total number of elementary transfers and E is the transfer inefficiency per elementary transfer. The curves are drawn for different spatial frequencies [/ is the Nyquist frequency (JJ2) ] and different array con-iigurations. The solid curves are for a staring array and the dashed curves for an array which uses series-parallel scan with TDl...

Lenses Lenses have their own modulation transfer function (MTF) characteristics that change with aperture of ( setting. 

Thus care is required in comparing results from different sources. The best method of determining resolution is to measure the (contrast in the image)/(contrast in the object) as a function of detail separation. This is the modulation transfer function (MTF), also called the contrast transfer function, which describes how the modulation or contrast in the object is transferred to the image. Clearly when MTF falls to some very small value no object detail is reproduced in the image. 

The geometrical resolution can be represented by the modulation transfer function (MTF). Basically, the MTF is the ratio between the true dimension of the object and the resolution of the images acquired. It is usually calculated from the measurements of a thin wire phantom which provides the point spread function of the system. A given point spread function is used to calculate the MTF. The MTF curves describe the ratio of the contrast in the CT or micro-CT image to the contrast in the object with respect to the spatial frequency. The MTF demonstrates the frequency components of a structure in line pairs per millimeter (Ip/mm). Normally, the MTF, and therefore the resolution of a CT system, is evaluated at 10% contrast difference (Fig. 6.7). 

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