Dose reduction in multidetector CT of the urinary tract. Studies in a phantom model

Abstract

A novel ureter phantom was developed for investigations of image quality and dose in CT urography. The ureter phantom consisted of a water box (14 cm x 32 cm x 42 cm) with five parallel plastic tubes (diameter 2.7 mm) filled with different concentrations of contrast media (1.88-30 mg iodine/ml). CT density of the tubes and noise of the surrounding water were determined using two multidetector scanners (Philips MX8000 with four rows, Siemens Sensation 16 with 16 rows) with varying tube current-time product (15-100 mAs per slice), voltage (90 kV, 100 kV, 120 kV), pitch (0.875-1.75), and slice thickness (1 mm, 2 mm, 3.2 mm). Contrast-to-noise ratio as a parameter of image quality was correlated with dose (CTDI) and was compared with image evaluation by two radiologists. The CT densities of different concentrations of contrast media and contrast-to-noise ratio were significantly higher when low voltages (90 kV versus 120 kV, 100 kV versus 120 kV) were applied. Smaller slice thickness (1 mm versus 2 mm) did not change CT density but decreased contrast-to-noise ratio due to increased noise. Contrast phantom studies showed favourable effects of low tube voltage on image quality in the low dose range. This may facilitate substantial dose reduction in CT urography.

Delineation of upper urinary tract segments at MDCT urography in patients with extra-urinary mass lesions: retrospective comparison of standard and low-dose protocols for the excretory phase of imaging

“…Thus, it appears that considerable dose reduction is possible when the primary task is to delineate the course of the upper urinary tract, e.g., for surgical planning in lesions outside of the urinary tract. Our finding corroborates earlier observations in phantom studies [10] and animal studies [11] that emphasize the option of considerable dose reduction at CTU in the excretory phase. They are in keeping with observations in patients with urolithiasis that demonstrate that there is no significant diagnostic loss associated with dose reduction by a factor of about 6 in unenhanced CTs of the abdomen [12,15].…”

“…administration of low doses of frusemide prior to CTU [6][7][8], and obtaining additional CT images in the excretory phase [9]. However, one major concern in CTU is additional radiation exposure due to (repetitive) CT data acquisitions in the excretory phase [3,10]. Experimental studies [10,11] and clinical experience in patients with urinary calculi [12] suggest that the high image contrast between dense matter within the urinary lumen (contrast media or urinary calculi) and surrounding tissue warrants considerable dose reduction at CTU without apparent loss of diagnostic quality.…”

CT urography: definition, indications and techniques. A guideline for clinical practice

“…While low kVp settings for dose-reduction have been recommended [50], they are still used infrequently in clinical practice. Tube load settings have varied significantly between groups, continents and machine types and have ranged from 50-300 mAs on 4-slice and 65-200 mAs on 16-slice CT systems.…”

“…Bae, presented at RSNA 2005). Furthermore, lower tube voltages of 90-100 kV have favourable effects on image quality (contrast-to-noise ratio) in the low-dose range [50].…”

Effect of various environments and computed tomography scanning parameters on renal volume measurements in vitro: A phantom study

“…However, the effect of low kilovoltage and low tube current on segmentation of solid organ has not been widely evaluated. A decrease in the X-ray tube voltage resulted in reduced amount of penetrating radiation, and thus an increase in object attenuation and image noise (28)(29)(30). Numerous studies have focused on the lower kilovoltage application in iodinated contrast agent CT scanning, since the lower kilovoltage imaging resulted in evidently higher attenuation of iodine (28,29).…”