All IP-Docs relevant  to Synchrotron, Undulator, FEL and CLS  have been searched, in the  on-line esp@cenet search-engine of the European Patent Office (EPO).

In total 872 relevant IP-Docs have been retrieved and evaluated. This search has led to the Idustrial Property Documents that constitute the innovation kernel of the present break-through in the field of Compact Light Sources and their implementation in a way that directly serves Medical Imaging and especially Cardiac Radiology, as a really disrupting technology, after  Wilhelm Conrad Röntgen and Sir Godfrey Newbold Hounsfield.

Figure 3 displays the temporal evolution of Tunable X-ray Systems related Industrial Property Documents since 1960, as searched on esp@cenet .

Figure 4 presents the Light-sources categories (Synchrotron, Undulator,  FEL and CLS) related numbers of the 872 in total retrieved and classified relevant Industrial Property Documents.

Figure 5 presents the US Patent 7277526 B2, "Apparatus, system, and method for high flux, compact compton x-ray source", granted to  Lyncean Technologies Inc., Palo Alto, 94306, California, USA. on October 2nd 2007.

This is the most important IP-Doc, so far, since it is the key-patent that describes the technologies that led to the development and recent (May 2015) installation of a CLS in a clinical environment in a common action of LMU/TUM in Munich.

In contrast to any conventional X-ray tube sources, the CLS intrinsically produces a narrow-band, nearly monochromatic and tunable X-ray spectrum.

The CLS is a LASER-driven X-ray source, based on the Thomson back-scattering of low-energy photons at high-energy electrons.

Energy is transferred from the electrons to the photons which are boosted into the X-ray region. This process is also commonly known as ‘‘inverse Compton scattering’’.

Inverse Compton scattering (ICS) is the scattering of electrons on photons. From a classical point of view, the process is referred to as “Thomson scattering” and can be visualized as a plane wave of frequency ω₀ impinging on an electron.

In the approximation where LASER-energy is much lower than rest electron energy (i.e., in the rest electron frame), the scattered electromagnetic wave frequency is conserved.

In the laboratory frame, as electrons are relativistic, the incident electromagnetic wave undergoes two frame changes, and its frequency is increased by a 4γ² factor, due to the relativistic Doppler effect.

In quantum electrodynamics, ICS is visualized as a succession of absorption and emission of a photon by an electron. In this approach we refer to “Compton scattering,” which lets us consider electron recoil and particle polarization.

The process is described as the collision between photons and electrons. This collision is elastic, so the interaction parameters can be calculated according to energy and momentum conservation.

The scattered photon energy is a complicated function of electron energy, LASER wavelength, collision, and scattering angles:

         E_x  = E_p(1-βcosθ₁) / [(1-βcosθ₂)+ E_p(1-βcos(θ₂ - θ₁)/Ε_e]

where E_X is the energy of the scattered photon, E_p is the energy of the  LASER photon, E_e is the energy of the electron, γ is the relativistic factor, θ₁ is the collision angle, and θ₂ is the scattering angle.

A small electron storage ring with a circumference of less than five meter, is filled with electron bunches at an energy of 25–45 MeV by a linear accelerator of about five meter length. The orbital frequency is 65 MHz.

The electron bunches are focused to about 40 mm diameter (rms) in a spot where the counter propagating LASER-beam of a bow-tie, high-finesse LASER-cavity is also focused. The LASER has a wavelength of about 1 mm.

The electrons oscillate in the electromagnetic field of the laser light like in the undulator field of an insertion device, at a synchrotron beamline. Due to the short period of this laser field, radiation in the keV energy regime is produced even by electrons of some MeV energy [7]–[12].

In a "conventional" synchrotron, an undulator with some centimeter field period, needs electrons in the GeV order of magnitude, in order  to produce keV X-Ray radiation.

With a beam divergence of 4 mrad and an energy bandwidth of 3% in the energy range of 15–36 keV, the radiation is perfectly suitable for high- and medium resolution radiographic and tomographic X-ray imaging applications.

Figure 6 presents a schematic view of the photon-electron interaction [13].

Figure 7 shows a front view of the CLS showing the injector (on the right), the transport line (on the left) and the electron storage ring (at the top). The length of the CLS is about 5 m[8].

Figure 8 presents a CAD drawing of the CLS with the electron storage ring and the optical cavity of the infrared laser system. The interaction point of the laser pulse and the electron pulse is emphasized[8].

Figure 9 presents (black, blue and green lines) the spectra of the FR591 rotating anode X-ray tube at peak voltages of 20, 30 and 60 kVp and (red line) the spectrum of the Compact Light Source at 21 keV[8].

Figure 10 displays histograms of the tomographic images of the water sample in a polypropylen container (phantom):Green, blue and black lines represent the frequency of absorption coefficients m for the measurement with the X-ray tube at 60, 30 and 20 kVp. Red line gives the values for the measurement with the CLS at 21 keV [8].

Figure 11 shows X-ray images of a variety of mammography test objects using absorption (left), phase-contrast (center) and dark-field (right) imaging modes. Different objects appear more clearly in one or another image, depending on the object’s structure [13]-[15].

Finally, in Figure 12 X-ray images of a mouse  using absorption (left), phase-contrast (center) and dark-field (right) imaging modes. Soft-tissue details are obviously better visible, compared to "classical" X-ray images.