Scan field of view

With this approach, constant temporal resolution equivalent to a quarter of the gantry rotation time is achieved in a centered region of the scan field of view. For trot= 0.33 s, the temporal resolution is t t/4 = 83 ms, independent of the patients heart rate. 

Fig. 1.5a,b. Schematic illustration of a dual-source CT (DSCT) system using two tubes and two corresponding detectors offset by 90°. A scanner of this type provides temporal resolution equivalent to a qiuirter of the gantry rotation time, independent of the patient s heart rate. In a technical realization, one detector (a) covers the entire scan field of view with a diameter of 50 cm, while the other detector (b) is restricted to a smaller, central field of view... 

Hsieh J, Chao E, Thibault J, etal. (2004) A novel reconstruction algorithm to extend the CT scan field-of-view. Med Phys 31 2385-2391... 

Ohnesorge B, Flohr T, Schwarz K, et al. (2000) Efficient correction for CT image artifacts caused by objects extending outside the scan field of view. Med Phys 27 39 46 Parker D (1982) Optimal short scan convolution for fanbeam CT. Med Phys 9 254-257... 

Two cylindrical phantoms were used for simulation. The small phantom was water phantom with a wall made of Perspex material. The external diameter of this phantom is 215 mm and its wall thickness is equal to 6 mm. The large utilized phantom was polypropylene phantom. This phantom that normally used for modeling of bony structures has 350 mm diameter, suitable for large scan field of views. 

From the early 1980s to present, infrared sensitive two dimensional arrays were mated to integrated circuits for signal processing and sensitivity to better than 0.03 K (see Photodetectors). These focal plane arrays of some 500 by 500 elements eliminate the need for scanning and provide good spatial resolution. Some versions have no special cooling requirements. The development trend is to increase the number of pixels to improve resolution, increase the field of view and keep the size and cost of the optics within acceptable bounds. 

This type of infrared instrument provides a single dimensional scan or line of comparative radiation. While this type of instrument provides a somewhat larger field of view, i.e. area of machine surface, it is limited in predictive maintenance applications. 

The field of view for the ultrasound equipment is rather small, typically, not more than 20-30 cm and just a few centimeters at higher spatial resolution. Normally, a cross-sectional image in the plane of the imaging probe is obtained. Respectively, the operator must know where to place the transducer to locate the area of an expected lesion, as compared with a whole-body CT, the wide flat view of planar X-ray or MRI scans. 

The sky map of the LMC region. The scan paths (dashed lines), the target position (+) for the offset pointing mode and the full field of view (2° x 4° ) are indicated. The thick solid rectangle shows the 90% confidence... 

Free Spectral Range Resolution. . . . Scanning Speed. . Field of View. . . Optics. ... 

Dedicated PET systems are usually based on lull ring detector systems with an axial field of view exceeding 15 cm, and can be operated in septa extended (2D mode) or septa retracted mode (3D) for patient examinations. Some systems only provide 3D-data acquisition modes. Most systems allow the simultaneous acquisition of 36 transversal slices and more with a theoretical slice thickness of 2-5 mm. Transmission scans for a total of 10 min are obtained prior to the radionuclide application, for the attenuation correction of the acquired emission tomographic images. All PET images are attenuation corrected and iteratively reconstructed. 

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