**3.1. Recent advances in SPECT and PET imaging systems**

The key technology in the development of SPECT and PET systems for static or dynamic image acquisition is embodied in the development of the detector, or rather, the detector chain. Although it has already reached a high degree of perfection, continuous improvements are still increasing the performance of, for example, the scintillator material, which is a critical component in the chain. The time of flight camera, introduced by Philips Medical Systems in the 1980s, is replacing the conventional Anger camera and offers significant improvements in image quality. The trend here is towards higher resolution where, for certain applications, 2048 x 2048 pixel matrices will be used. In addition to continuous improvements in the detector chain, there are also radically novel approaches which dispense with the need for a semicon‐ ductor detector. A detector based on scintillator crystals coupled to hybrid photodetectors that provides full 3D reconstruction in PET imaging with high resolution and avoiding parallax errors developed during last ten years are actually available [29, 30].

Another improvement is SPECT systems provision on a single stand of rotation of several (two or three) detecting heads, allowing examination time reduction and detection sensitivity increasing. In addition, one of the heads can record a transmission coefficient image induced by a radioactive external gamma source photons of the same energy as those issued by the tracer during the examination. These acquisitions are then used to correct the effect of selfabsorption.

Development of SPECT and PET systems much more efficient enable major advances in the clinical use of these techniques with very widespread applications field. Additional develop‐ ment may include research on more efficient scintillators, the use of more adequate recording geometries, such as the conical geometry for example, accompanied sure with the development of robust reconstruction algorithms.

GE offers a variation in its range of PET-CT "Discovery ST" machine to meet the specific clinical needs. After the Discovery ST oriented oncology and cardiology, the GE Discovery VCT sells dedicated cardiology is associated with a 64-slice scanner. The latest version offers a higher spatial resolution responding to neurological applications. GE ST machines are available in versions scanner 4, 8 or 16 cups. The 2D acquisition abandoned by other manufacturers is optional and defended by GE to obtain less noisy images (useful for some advanced applica‐ tions or for overweight patients) and for new applications mostly outside the scope FDG. GE believes that the increase of activity of PET-CT will be around 50% in the next three years and examines the association of PET and MRI modalities. The contribution of MRI compared to

Principles and Applications of Nuclear Medical Imaging: A Survey on Recent Developments

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PHILIPS GEMINI PET/CT scanners combine the Brilliance CT technology, that is well-suited to cardiac imaging with its wide-coverage submillimeter imaging, ultra fast acquisition times and Rate Responsive image acquisition technology that adapts to the patient's heart rate and rhythm during acquisition. GEMINI PET/CT scanners deliver high spatial resolution and high sensitivity PET imaging resulting in improved image quality when imaging the short-lived radiopharmaceuticals used with cardiac PET. Philips PET-CT hybrid machines ALLEGRO

SIEMENS works to upgrade the install PET-CT around the world. The range of PET-CT, BIOGRAPH marketed since 2000 continues to benefit from developments. After improving the sensitivity BGO crystals by replacing the LSO crystals, SIEMENS in 2004 increased the detection speed by introducing a new channel detection (PICO 3D) with the coincidence window is only 4.5 ns and improved spatial resolution due to detector Hi-Rez (block 13 x 13 x 8 against 8 elements far). Note that BIOGRAPH have a tunnel of 70 cm diameter field used

A variety of SPECT-CT scanners are nowadays available in many hospitals and oncology centres (Figure 10). GE proposes a robust SPECT-CT hybrid machine called "Infinia" which is a dual-head, large field for general applications. The Infinia has an open stand. It is available with SPECT thick crystals (5/8th) or thin (3/8th) depending on the intended application. It is available in solo or in combination with a scanner. The Infinia Hawkeye 4 SPECT/CT from GE

in whole to acquire PET scanner. This criterion is important for obese patients.

CT is questionable, except perhaps in functional imaging.

maintain in the range GEMINI.

**Figure 9.** Example of commercially PET-CT scanners.

*3.1.2. SPECT-CT*

Time-of-Flight technology has always held the promise of better PET imaging. Philips delivered on that promise with its innovative Astonish TF technology. Now with 4D TOF, Philips continues to push the envelope of PET imaging performance. See how 4D TOF Innovation is making an impact on PET imaging.

Design of Hybrid machines has been a very interesting research and technologic development axe in nuclear imaging during last fifteen years. Indeed, many hybrid PET-CT, SPECT-CT and PET-MRI machines were manufactured offering a variety of very interesting diagnostic applications by the combination of results of two imaging methods allowing the revelation of a very interesting pathologic information that cannot be revealed by a single technique alone. PET-CT is creating a new benchmark in imaging and analysis of cardiovascular disease. PET-CT enables the combination of PET myocardial perfusion and viability imaging with CT coronary angiography and calcium scoring in a single integrated environment. In oncology, it provides the integration of metabolic data from PET and anatomical data from CT.

SPECT-CT is a system designed entirely for nuclear medicine and has particular value in the cardiology cycle of care. This hybrid machine allows table to remain stationary in many cases, eliminating complexities inherent in table indexing, acquires the entire heart volume in just one rotation and permits patients to breathe normally during SPECT and CT acquisitions. In oncology, it plays an important role in diagnosis, treatment, and follow-up in the oncology cycle of care, including the use of low-dose localization and aids better visualization that is especially valuable during studies and in bone imaging.

Researchers continue to develop new ways of using PET. One recent development has been the combination of PET and MRI2 into a single apparatus. Compared to CT, MRI generally provides more detailed images, which can aid in the more precise localization of cancerous growths. A hybrid PET-MRI scanner simultaneously delivers functional information plus anatomy and tissue characterization (soft tissue contrast and blood vessel physiology), from a state-of-the-art MRI scanner. At the same time, it provides metabolic imaging from PET technology. Fusing these images gives the best of both worlds, providing greatly superior information to what you'd get from either machine individually

Actually, the main hybrid machines routinely used in hospitals are the following:
