Intravenous arteriography using digital subtraction techniques.

The application of digital computers to electronic x-ray imaging devices has rejuvenated interest in the field of intravenous arteriography. By utilizing computer image subtraction techniques, digital roentgenographic systems based on fluoroscopy or computed tomography (scanned projection radiography) provide significantly improved vascular imaging compared with conventional film subtraction methods. Digital subtraction angiography schemes isolate contrast media in the vessel by detecting differences in images obtained before and after the injection of contrast medium or changes in the relative attenuation of contrast media at different x-ray energies.

Performance of x-ray imaging systems applied to intravenous angiography.

A review is made of the performance of X-ray systems applied to the imaging of dilute amounts of iodine using subtraction methods. Relevant performance criteria are defined and desired performance levels are derived. For a general purpose system these are iodine sensitivity of 1 mg/cm2, cancellation of 10 g/cm2 soft tissue and 2 g/cm2 bone to be equivalent to iodine sensitivity, capability of imaging through 25 cm soft tissue, spatial resolution exceeding 1 lp/mm and acceptable imaging time depending on the application.

Intracranial intravenous digital subtraction angiography.

Intravenous digital subtraction angiography (iDSA) promises to significantly alter the use of conventional cerebral angiography in the workup of neurological patients. Understanding its diagnostic potential and its limitations are important in incorporating this new examination into the diagnostic thought process of neuroradiologic tests. Different image processing techniques such as integration of mask and contrast images promise to improve image quality for neuroradiologic application.

Generalized image combinations in dual KVP digital radiography.

Dual energy basis decomposition techniques apply to single projection radiographic imaging. The high and low energy images are non-linearly transformed to generate two energy-independent images characterizing the integrated Compton/photoelectric attenuation components. Characteristic linear combinations of these two basis images identify unknown materials, cancel known materials, and generate synthesized monoenergetic images.

Three-beam K-edge imaging of iodine using differences between fluoroscopic video images: experimental results.

In an earlier article we discussed the rationale for using differences between video images in three-beam selective iodine K-edge imaging. Rather than combining three initial images Li linearly to yield the final image k1L1 + k2L2 + k3L3, differences between the Li were first generated and then combined either to linear or quadratic order. This approach was motivated by the desire to suppress the large multiplicative biases of fluoroscopic imaging and justified by theoretically proving that k1 + k2 + k3 is approximately equal to 0.

Three-beam K-edge imaging of iodine using differences between fluoroscopic video images: theoretical considerations.

Our lab has previously generated selective iodine images with an image intensifier fluoroscopic system using a three-beam K-edge approach. Logarithmically amplified video images Li were linearly combined to yield the final image k1L1 + k2L2 + k3L3. This paper discusses refinements of the K-edge technique.

Application of the noise power spectrum to positron emission CT self-absorption correction.

Two methods are compared in correcting for self-absorption in positron emission CT scans, or equivalently, in determining the integral of attenuation along a strip in a cross section. These are CT reconstruction and direct measurement. It is shown that the former method is slightly more precise than the latter with the degree of improvement proportional to the number of angles used.

Limitations to iodine isolation using a dual beam non-K-edge approach.

In dual-beam selective iodine imaging, images of an object are made with each of two spectrally different x-ray beams. The mean beam energies may either straddle the 33 keV iodine K-edge or both lie above the K-edge. Both patient exposure considerations and the availability of sufficient x-ray flux make the latter approach favorable for tissue thicknesses exceeding 5 cm.

A hybrid computerized fluoroscopy technique for noninvasive cardiovascular imaging.

The excellent linearity of digital image storage and retrieval permits hybrid analog-digital subtraction to extend the spatial resolution of two previously developed algorithms which employed entirely digital apparatus. A low resolution, time-integrated preinjection digital mask image is reconverted to analog form and subtracted from live analog video images of iodine administered by peripheral intravenous injection to produce a high resolution display of the cardiovascular system with contrast ten times greater than conventional fluoroscopy. Preliminary studies in dogs are compared with images obtained with our digital subtraction algorithms.

Computerized fluoroscopy techniques for intravenous study of cardiac chamber dynamics.

A computerized fluoroscopy system which was recently developed in our laboratories permits image contrast increases of 8-16 relative to conventional image intensifer fluoroscopy and permits study of canine and human ventricular wall motion using peripheral intravenous injections. Two time-dependent image subtraction algorithms are illustrated in connection with observation of artificially infarcted dog hearts. The first algorithm produces a display analogous to direct ventriculography using catheterization.

Real-time digital K-edge subtraction fluoroscopy.

We report in vitro and in vivo trials of K-edge fluoroscopy, by which iodine contrast concentration is displayed live, with tissue and bone images suppressed, free of patient-motion artifacts. Iodine and cerium, 125 and 225 mg/cm2 respectively, filter alternate TV fields of cine-pulsed 50 KVP x-rays. Weighted subtraction of successive TV fields isolates the iodine image and simultaneously minimizes artifacts.

The noise power spectrum in computed X-ray tomography.

An expression is derived showing that the two-dimensional noise power spectrum of computed X-ray tomography is proportional to [G(k)]2/k where k is the radial spatial frequency and G(k) is the one-dimensional corrective filter used in the filtered back-projection reconstuction technique. It is shown that predicted noise power spectra compare well with those estimated from CT reconstructions of simulated noise for both the ramp filter and the Hanning-weighted ramp filter. A consequence of the non-uniform shape of the noise power spectrum is that statistical noise in CT reconstructions is correlated from point to point.

Selective iodine imaging using K-edge energies in computerized x-ray tomography.

Iodine is commonly used as a contrast material in computerized x-ray tomography. In some cases the determination of the iodine distribution in the image may be prevented by the presence of bone or tissue variations within the tomographic slice. This paper describes a method for quantitative selective imaging of the iodine concentration in the slice.

Digital K-edge subtraction radiography.

K-edge subtraction images have been produced using a digital video image processor. Images formed by three filtered x-ray beams are detected by an image intensifier-Plumbicon system, digitilized, and combined in real time to produce bone- and tissue-free K-edge subtraction images of iodinated structures. Preliminary studies of rhesus monkey cranial, spinal, and abdominal structures are compared with those of conventional radiography.

Relative properties of tomography, K-edge imaging, and K-edge tomography.

The properties of tomography, K-edge imaging, and K-edge tomography are discussed in relation to the imaging of small concentrations of elements such as iodine and xenon and are compared by means of phantom images. It is demonstrated that the complementary selectivities provided by depth and energy subtraction are combined in K-edge tomography. Using a three-spectrum subtraction technique, the iodine difference signal predicted by computer calculations is on the order of 8000 times that of an equal concentration fo bone.

Spectral considerations for absorption-edge fluoroscopy.

In our previous reports on absorption-edge fluoroscopy, it was not possible to relate fully the subtleties involved in the selection of spectral parameters. This paper is intended as an overview of this important aspect of the technique. It is shown that, by using the 1-kVp, 2-filter technique, it is possible to image certain elements (e.

Noise due to photon counting statistics in computed X-ray tomography.

A general expression is derived for the noise due to photon counting statistics in computed X-ray tomography. The variance is inversely proportional to the cube of the resolution distance. For scanners using a water box, the noise in the reconstructed image depends inversely on the number of detected primary photons, summed over all angles, that have passed through a resolution element.