Studio delle prestazioni di un sistema a fosfori per mammografia ...

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a cassette reader and a touch screen display for easy adjust of the readout process parameters and operation selection (see Fig. 3.5). Figure 3.5: The FUJI FCR5000. The IP handling unit furnishes the cassette with shock absorbing clothes to prevent scratch- ing of the IP. In addition to IP cleaning brush rollers positioned on both sides of the IP, it has also cleaning guides to prevent dirtying of the plate and minimize the possibility of image im- pairment by dust. In the configuration used during this work, the image reader was connected to an external controller (based on a personal computer) equipped with an image processor. The controller was connected also to a film printer and to a graphical workstation by means of a network system. The graphical workstation was based on a further PC, dedicated to image storage, and a pair of high definition clinical diagnosis monitors manufactured by Barco. The controller has further features, regarding the image ID registrations and the image acquisition and processing setup. The hardware dimensions of the FCR5000 MA are 730 mm width, 700 mm depth and 1565 mm height, for a total weight of 280 Kg. The feed/load time specified for the high resolution 39
Figure 3.6: The graphical workstation equipped with a pair of Barco high resolution monitors and, on the right, the controller. 18cm¢24cm cassette is about 72 sec, corresponding to a processing capability of about 48 IPs/hour. This reading rate is one of the items that need to be improved in order to provide good clinical use performances, where higher readout rates are desired. 3.4 IP cassette and photostimulable storage plate The cassette holding the imaging plate has been designed to cope with the specifications of a dual light collection mammographic system. The IP is not easily accessible from the exterior during normal operation and the body is a tight light enclosure. Anyway a fully-openable design is employed to facilitate interior cleaning. For the protection of both IP surfaces, shock absorbing clothes are affixed on the back surface as well as the front surface. The cassette is available in two sizes ( � ¢ �cm and � ¢ cm ), with the same dimensional standards of the conventional film plate cassettes, so to allow their use in pre-existing X-ray units. A picture of the IP cassette used in this work is shown in Fig. 3.7. A bar-code label is attached to the cassette body for IP identification purposes. When used with an external controller, the whole system allows a bar code identification procedures that prevents the user from possible mistakes and makes easier the input of the patient parameters and the association of the image information with the readout data. The photostimulable storage plate is comprised of a barium fluorobromide/iodide (BaFBr ��I � �) compound with an activator (Europium) [16]. The high resolution dual side (HR-BD) reading plate thickness is about 30 % greater with respect to the single side reading plate (� �m), 40
Page 1 and 2: UNIVERSITÀ DEGLI STUDI DI FIRENZE
Page 3 and 4: 3.6 Histogram analysis and IP sensi
Page 5 and 6: made, allowing the diffusion of the
Page 7 and 8: Figure 1.1: Block diagram of the im
Page 9 and 10: function and to replace the very ge
Page 11 and 12: energy of the proper wavelength by
Page 13 and 14: Figure 1.4: Energy levels of the PS
Page 15 and 16: Figure 1.5: Single-side reading met
Page 17 and 18: digital levels. The system under in
Page 19 and 20: ¯ multiplying � Ü� Ý by a co
Page 21 and 22: frequency properties of our system.
Page 23 and 24: on the gain £ and on the function
Page 25 and 26: (a) (b) (c) -u N MTF pre MTF pre -u
Page 27 and 28: (a) (b) (c) -u N -u N -u N MTF p re
Page 29 and 30: -2u N Re { OTF } dig u1 u2 u3 uN 2u
Page 31 and 32: for every exposition. The output va
Page 33 and 34: The experimental data will be analy
Page 35 and 36: Console Value Measured Value (kVp)
Page 37 and 38: mAs Dose (�Gy) mAs Dose (�Gy) 2
Page 39 and 40: Al thickness Dose (mm) (�Gy) 0.0
Page 41: (a) (b) Figure 3.4: X-ray spectrum
Page 45 and 46: theless a set of cassettes has been
Page 47 and 48: ing plate is very wide, a variable
Page 49 and 50: Chapter 4 Measurement of the physic
Page 51 and 52: Figure 4.1: Section along the short
Page 53 and 54: Figure 4.4: Pixel Value plotted as
Page 55 and 56: was filtered by a 30 mm block of PM
Page 57 and 58: 17 13 9 5 1 18 14 10 6 2 19 15 11 7
Page 59 and 60: y the pixel size (� �m) and the
Page 61 and 62: Figure 4.13: Comparison between MTF
Page 63 and 64: 4.3 EMTF The phase dependence of Å
Page 65 and 66: Figure 4.18: Differences between EM
Page 67 and 68: Figure 4.20: 2 dimensional NPS The
Page 69 and 70: The Noise Equivalent Quanta was com
Page 71 and 72: Figure 4.26: NEQ scan vs NEQ subsca
Page 73 and 74: Figure 4.29: DQEsubscan. In Fig. 4.
Page 75 and 76: Conclusions The work performed in t
Page 77 and 78: Bibliography [1] M.J. Yaffe and J.A
Page 79 and 80: [21] “Characteristics of digital

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