A patient-centric approach to quality control and dosimetry in CT including CBCT.

One measurement and an algebraic formula are used to calculate the incident air kerma (Ka,i) at the skin after any CT examination, including cone-beam CT (CBCT) and multi-slice CT (MSCT). Empty scans were performed with X-ray CBCT systems (dental, C-arm and linac guidance scanners) as well as two MSCT scanners. The accumulated Ka,i at the flat panel (in CBCT) or the maximum incident air kerma at the isocentre (in MSCT) were measured using a solid-state probe. The average Ka,i(skin), at the skin of a hypothetical patient, was calculated using the proposed formula. Additional measurements of dose at the isocentre (DFOV) and kerma-area product (KAP), as well as Ka,i(skin) from thermoluminiscence dosimeters (TLDs) and size-specific dose estimates are presented for comparison. The Ka,i(skin) for the standard head size in the dental scanner, the C-arm (high dose head protocol) and the linac (head protocol) were respectively 3.33 ±â€¯0.19 mGy, 15.15 ±â€¯0.76 mGy and 3.23 ±â€¯0.16 mGy. For the first MSCT, the calculated Ka,i(skin) was 13.1 ±â€¯0.7 mGy and the TLDs provided a Ka,i(skin) between 10.3 ±â€¯1.1 mGy and 13.8 ±â€¯1.4 mGy. Estimation of patient air kerma in tomography with an uncertainty below 7% is thus feasible using an empty scan and conventional measurement tools. The provided equations and website can be applied to a standard size for the sake of quality control or to several sizes for the definition of diagnostic reference levels (DRLs). The obtained incident air kerma can be directly compared to the Ka,i from other X-ray modalities as recommended by ICRU and IAEA.

Exact calculation of the minimal exposure for the secure detection of a transmission contrast signal.

In contrary to conventional screen film radiography digital radiographic methods allow the flexible adaptation of the visualisation of an image to a clinical question even after its generation. Nevertheless, the information content of an image is in addition to covering effects like anatomical noise ultimately limited by the applied exposure, its energy distribution and the dose to the detector. This limitation needs to be analysed quantitatively and in connection with efficiency properties of the image generation process. The random variation of pixel values in plane digital radiography is in general attributed to the limited number of imaging quanta. This allows determining a minimal number of applied quanta from requirements to the image information. The number of applied quanta is closely related to the entrance dose. It can be calculated by understanding the imaging process as the sum of many binomial sampling processes. This approach is useful for the separation and examination of the influences of the transmission, absorption and scattering properties of an imaging setup, including the used radiation quality. The model imaging task examined here is the detection of a thin contrast layer of one material behind a homogeneous main absorber of a second material by projection radiography. As the physical properties of the setup are dependent on the energy of the applied radiation, the energy leading to a minimal number of applied photons to achieve the required information can be calculated. It turns out to depend on the materials of both but on the thickness of only the main absorber. The efficiency of the exposure by other energies can be determined as the ratio between the minimal number and the number of quanta needed to achieve the same information. For monoenergetic exposures it is shown that changing the optimal energy by a fixed factor leads to the same loss of efficiency independent of the thicknesses of contrast layer and main absorber. The efficiency of the detection process can shift the optimal position. It directly follows that the optimal range of photon energy becomes smaller for thinner specimens. This clearly stresses the need for an adaptation of the applied energies to the physical properties of the patient especially when thin objects are examined.

Epidemiologic study of insecticide exposures, obesity, and risk of bladder cancer in household dogs.

A case-control study of household dogs was conducted to determine if exposure to sidestream cigarette smoke and chemicals in the home, use of topical insecticides, and obesity are associated with the occurrence of bladder cancer. Information was obtained by interview from owners of 59 dogs with transitional-cell carcinoma of the bladder and 71 age- and breed size-matched control dogs with other chronic diseases or neoplasms. Bladder cancer risk was unrelated to sidestream cigarette smoke and household chemical exposures. Risk was significantly increased by topical insecticide use (OR = 1.6 for 1-2 applications per year and OR = 3.5 for greater than 2 applications per year; chi 2 trend; p = .008). This risk was enhanced in overweight or obese dogs. Further studies of this canine model may facilitate identification of specific carcinogens present in insecticides commonly used on pet animals and in the environment.