In recent years, almost all equipment vendors have introduced some techniques to reduce overranging including, for instance, dynamic/adaptive beam collimators, hybrid reconstruction algorithms or by setting restrictions on detector sections [1,2]. These have proven to work properly reducing the overranging dose approximately 50% for high (> 1) pitch values [3, 4, 5]. However, information is missing concerning the performance of modern anti-overranging systems for clinically-relevant pitch, collimation and rotation time values. Using the C2i santé database, overranging was computed from online exposure data and measured...

In helical CT, overranging is the difference between total exposed scan length and total imaged scan length (cf. [Fig 1]). To assess overranging, several approaches exist; some rely on displayed data at CT console [1,2], while others measure the dose profile using computed radiology (CR) imaging plates or Gafchromic films [2,6,7,8], or even through in-air ionization chamber measurements [2,5,9,10,11,12] or finally considering more elaborated measurements suitable for modern tomographs equipped with dynamic z-collimation [13]. In the present work, overranging length (LOR) was defined and computed...

For a typical head protocol, overranging was found to be equal to 1.63 cm for the GE Revolution Evo 64 model (0.531 pitch, 20 mm collimation, 1 s rotation time), 1.07 cm for the Siemens Somatom Definition AS+ 128 CT (0.55 pitch, 38.4 mm collimation, 1s rotation time) and 5.6 cm for the Philips Ingenuity Core 128 CT scan (0.394 pitch, 40 mm collimation, 0.4s rotation time). As expected, these values were respectively of 4.66 cm (1.375 pitch, 40 mm collimation, 0.5s rotation time), 3.32...

The four parameters affecting overranging are pitch (67% overranging increase for a pitch increase from 0.5 to 1.2), collimation (64% overranging increase for a collimation increase from 24 mm to 38.4 mm), rotation time (7% overranging increase for a rotation time increase from 0.5s to 1s) and own technology of the CT scan vendor (type/efficiency of dynamic collimation system). When comparing the scan models, it is also worth noting that, for very similar and almost identical acquisition parameters, overranging can be as low as 1.09...

[1] Schilham A, van der Molen AJ, Prokop M, de Jong HW. Overranging at Multisection CT: An Underestimated Source of Excess Radiation Exposure <sup/>. RadioGraphics. Juill 2010;30(4):1057‑67. [2] Trevisan D, Bonutti F, Ravanelli D, Valentini A. Real time evaluation of overranging in helical computed tomography. Phys Med. 1 déc 2014;30(8):968‑72. [3] Deak PD, Langner O, Lell M, Kalender WA. Effects of Adaptive Section Collimation on Patient Radiation Dose in Multisection Spiral CT. Radiology. 1 juill 2009;252(1):140‑7. [4] Booij R, Dijkshoorn ML, van Straten M. Efficacy...

L. A. GONZALEZ MENDEZ: Nothing to disclose J. Bozec: Nothing to disclose I. Rousselle: Nothing to disclose B. Royer: Nothing to disclose A. Noel: Nothing to disclose J. Farah: Nothing to disclose