Optical coherence tomography is one of a class of optical tomographic techniques. Its location can be identified with computed tomographic angiography. HRCT is performed using a conventional computed axial tomographic scanner without injection of contrast agents. Later, the substance was used in dedicated positron tomographic scanners, to yield the modern procedure. Tomographic imaging techniques were further developed at the Washington University School of Medicine. The mathematical basis for tomographic imaging was laid down by Johann Radon. There are several types of tomographic optical system including the parallel beam irradiation optical system. Colonoscopy is usually preferred to computerized tomographic colonography. The reconstruction is also called 'quantum tomographic reconstruction'. These systems are capable of tomographic studies as well as mapping horizontal patterning. This is called a tomogram, or tomographic reconstruction. This creates a fast anomaly that is visible in tomographic images. Regional to global scale tomographic models are generally based on long wavelengths.