In previous labs, it was demonstrated that a high kilovoltage (kV) results in scatter radiation. In order to acquire sufficient penetration, a high kV is oftentimes needed. To reduce the amount of scatter caused from the increase in kV, a grid can used. According to Carlton and Adler (2013), “a grid is designed to absorb the unwanted scatter radiation” (p.259).
To demonstrate how grids affect density, contrast, and patient dose, four labs were performed using an abdomen phantom and a pelvis phantom. Both film screen and digital image receptor systems were used, both with a 14” x 17” cassette. The experiments were performed tabletop and in the Bucky tray with varying grid placement, using a 400-speed screen system. The source to image receptor …show more content…
Performed tabletop, the base radiograph was exposed at 5 mAs (200 mA at 25 ms) with 75 kV. This film was adequately penetrated and exposed; however, scatter was present. Using the Bucky tray with an 8:1 grid ratio, Film 2 was exposed using the base technique. Film 2 was adequately penetrated but underexposed. It resulted in decreased density, increased contrast, and consistent patient dose. Film 3 was also exposed in the Bucky tray, but the grid conversion factor was applied. According to Johnston and Fauber (2016), “the grid conversion factor can be used to determine the adjustment in mAs needed when changing from using a grid to non-grid or for changing to grids with different ratios” (p.148). It was exposed at 20 mAs (400 mA at 50 ms) with 75 kV. This allowed density to be maintained with a much higher scale of contrast. Patient dose increased by a factor of 4. Using a 16:1 stationary grid, film 4 was exposed at 30 mAs (300 mA at 100 ms) with 75 kV. While density was maintained with the GCF, film 4 showed the highest contrast and patient dose. Film 4 had visible grid lines because a stationary grid was …show more content…
The base radiograph was performed tabletop and exposed at 3.2 mAs (320 mA @ 10 ms) with 80 kV providing an exposure index (EI) number of 485. Using the Bucky tray, which contained a 12:1 grid ratio, image 2 was exposed with the same technique as the base. Image 2 was adequately penetrated but underexposed with an EI number of 170. Image 3 was also exposed in the Bucky tray, but the GCF was applied. It was exposed with 15 mAs (300 mA @ 50 ms) with 80 kV and an EI number of 452. Density and receptor exposure were maintained while contrast and latitude increased. For image 4, a stationary grid with a 16:1 grid ratio was used. Grid lines were visible. Using the GCF, technique was manipulated to 18 mAs (200 mA @ 90 ms) with 80 kV and an EI number of 420. It produced the highest contrast, and patient dose increased by a factor of 6. While grids “improve the contrast of the radiographic image by absorbing scatter radiation”, the grid conversion formula must be used to maintain density (Verhovsek, 2017, s.3). This, in turn, increases patient