A : This paper outlines image domain material decomposition algorithms that have been routinely used in MARS spectral CT systems. These algorithms (known collectively as MARS-MD) are based on a pragmatic heuristic for solving the under-determined problem where there are more materials than energy bins. This heuristic contains three parts: (1) splitting the problem into a number of possible sub-problems, each containing fewer materials; (2) solving each sub-problem; and (3) applying rejection criteria to eliminate all but one sub-problem's solution. An advantage of this process is that different constraints can be applied to each sub-problem if necessary. In addition, the result of this process is that solutions will be sparse in the material domain, which reduces crossover of signal between material images. Two algorithms based on this process are presented: the Segmentation variant, which uses segmented material classes to define each subproblem; and the Angular Rejection variant, which defines the rejection criteria using the angle between reconstructed attenuation vectors.

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Pakistan has been trapped by a blend of problems such as political chaos, economic turmoil, social unrest, religious extremism, rampant corruption, unemployment, pervasive poverty, child labor, moral degeneration, etc. The energy crisis has added fuel to the fire; it has created many more socio-economic issues for the whole nation. This research study has highlighted the impact of the energy crisis in Pakistan particularly on its society and economy. It has enunciated that the energy crisis has deteriorated the social setup in Pakistan as it has disturbed the domestic routines, institutional schedules, health facilities, transportation system and educational procedures. Similarly, the crisis has pushed Pakistan into an economic decline. Most of the local and foreign investors have migrated to other states due to the non-availability of electricity, gas and petroleum products. Resultantly, Pakistan is experiencing the lowest ebb of Foreign Direct Investment (FDI). Unannounced load-shedding has not only discouraged the industrialists but also has decreased the ratio of production- a severe setback to the rate of exports. Non-availability of energy has decreased the ratio of agricultural productivity that has a significant share in the gross domestic product (GDP) of Pakistan. The cottage industry has also fallen victim to the energy crisis. In this way, there is a restrained flight of foreign capital to the country. In the end, the study has recommended some policies which can be formulated and practiced by the ends of both the government and the public to discard the energy crisis.

Energy resolving performance of spectral CT systems is influenced by the accuracy of the detector's energy calibration. Global energy calibration maps a given threshold to the average energy response of all pixels of the detector. Variations arising from CMOS manufacturing processes and properties of the sensor cause different pixels to respond differently to photons of the same energy. Threshold dispersion adversely affects spectral imaging by degrading energy resolution, which contributes to blurring of the energy information. In this paper, we present a technique for per-pixel energy calibration of photon-counting x-ray detectors (PCXDs) that quantifies the energy response of individual pixels relative to the average response. This technique takes advantage of the measurements made by an equalized chip. It uses a known global energy map to quantify the effect of threshold dispersion on the energy response of the detector pixels across an energy range of interest. The proposed technique was assessed using a MARS scanner with an equalized Medipix3RX chip flip-bonded to 2 mm thick CdTe semiconductor crystal at a pitch of 110 μ m. Measurements were made of characteristic x-rays of a molybdenum foil. Results were compared between the case that the global calibration was used on its own and the case of using it in conjunction with our per-pixel calibration technique. The proposed technique quantified up to 1.87 keV error in energy response of 100 pixels of a selected region of interest (ROI). It made an improvement of 28.3% in average FWHM. The additional information provided by this per-pixel calibration technique can be used to improve spectral reconstruction.