Radiation dose evaluation in multidetector-row CT imaging for acute stroke with an anthropomorphic phantom

Abstract

ABSTRACT. This study evaluated radiation dose and dose reduction in CT imaging for acute stroke. Radiation doses in three types of CT imaging (i.e. non-contrast-enhanced CT, CT perfusion (CTP) and CT angiography (CTA)) were measured with an in-phantom dosimetry system for 4-, 16-and 64-detector CT scanners in 5 hospitals. To examine the relationship between image quality and radiation dose in CTA, image contrast-to-noise ratio was evaluated. Doses to the brain, lens, salivary glands and local skin obtained with scan protocols in routine use were: 42-71 mGy, 30-88 mGy, 3.9-7.3 mGy and 40-97 mGy in non-contrast-enhanced CT; 41-75 mGy, 9.9-10 mGy, 1.5-2.1 mGy and 107-143 mGy in CTP; and 8.2-55 mGy, 26-69 mGy, 2.0-73 mGy and 32-72 mGy in CTA. For the combination of these CT examinations, on average a patient would receive 236 mGy for the maximum local skin dose and 4.2 mSv for the effective dose evaluated by the International Commission on Radiological Protection (ICRP) 103. Effective doses in CTP in this study were less than those obtained with representative protocols of Western countries. Average effective doses in each CT examination were not more than 1.5 mSv. The use of reduced kV and a narrow scan range would be effective in dose reduction of CTA and CTP, and intermittent scanning would be essential in CTP. Although lens and maximum local skin doses were far less than the thresholds for deterministic effects, since radiation risks would be increased in repeated CT examinations, efforts should be devoted to dose reduction in stroke CT examinations. Most patients with suspected stroke undergo either CT or MRI as the initial diagnostic examination [1,2]. MRI has some advantages over CT in depicting stroke lesions; however, the provision of MR scanners in general hospitals is still low, an examination takes more time and patients with pacemakers cannot undergo MRI examinations. While CT techniques carry the risk of radiation exposure, CT scanners are nearly always available [3] and scans can be done quickly. Schramm et al [4] have reported that CT images obtained by the combination of various CT examinations allow diagnostic assessment of acute stroke with a quality comparable with that of stroke MRI. So CT examination has some advantages for the diagnosis of acute stroke patients who have no time to lose.The diagnostic CT examination for acute stroke generally requires three imaging techniques: non-contrast-enhanced CT of the head; CT perfusion (CTP); and CT angiography (CTA) of intracranial vessels. In these CT examinations the local skin dose in CTP might be considerably high. In a previous study we reported that the maximum skin dose was as high as 712 mGy, 13 times higher than that in non-contrast-enhanced CT of the head [5]. Although the latest multidetector-row CT (MDCT) scanners have a dose reduction function of intermittent scanning or shuttle scanning, detailed patient doses using the function have not been reported.The CTA technique has been developing with great potential owing to high scan speed and ...

The effect of head size/shape, miscentering, and bowtie filter on peak patient tissue doses from modern brain perfusion 256‐slice CT: How can we minimize the risk for deterministic effects?

“…Zhang et al 4 reported peak dose to eye lens and skin of 81 and 87 mGy, respectively, for the Philips Briliance 64 CT scanner at 80 kVp and 3750 mAs. Corresponding values found here for Philips Briliance iCT 256-slice CT scanner were 35% and 28% higher which may be attributed mainly to the double z-coverage allowed by the later scanner, i.e., 80 vs 40 mm, and secondarily to the 7% lower value of total mAs assumed in the study of Zhang et al 4 Compared to current results, Yamauchi-Kawara et al 8 and Cohnen et al 9 reported peak eye-lens doses lower by a factor of 10 which may be mainly attributed to the exclusion of the eye lenses from the primarily exposed head region. The range of the reported peak eyelens dose when eyes are primarily exposed is 81-279 mGy whereas the corresponding range when the eyes are not primarily exposed is 9.9-19.8 mGy.…”

“…Therefore, reporting of peak tissue doses to skin, eye lens, brain parenchyma, and RBM may be far more important than an estimate of effective dose in brain perfusion CT studies. Despite, peak skin and peak eye-lens doses from brain perfusion CT studies have been reported in a few recent studies, 4,8,9 reported data on peak doses to brain and RBM are scanty. Besides, published dose data refer mostly to low-dose brain perfusion CT studies performed on MD CT systems with up to 64 detector rows.…”

Should CT Angiography be a Routine Component of Acute Stroke Imaging?

“…On the other hand, all patients who are examined with CTA are exposed to its risks, which include an approximate doubling of the radiation dose, contrast exposure, and incidental findings such as unruptured aneurysms, thyroid nodules, and lung nodules. 23 Emergent CTA protocols require injection of iodinated contrast without a laboratory assessment of renal function. Patients run a risk of developing contrast-induced nephropathy, especially if they have underlying chronic kidney disease (CKD).…”

Improved accuracy of quantitative parameter estimates in dynamic contrast-enhanced CT study with low temporal resolution

“…14 To reduce radiation dose to patient during a DCE-CT scan, one can simply reduce tube voltage and tube current-exposure time product (mAs). [15][16][17] However, the associated image usually suffers from low signal to noise due to reduced current (mAs) and the radiation dose to patient could paradoxically increase if a study is repeated due to poor image quality. 17 In recent years, several studies reported the effectiveness of iterative reconstruction methods on low dose (low mAs) perfusion CT imaging for better image noise reduction, lowcontrast object detection, and, more importantly, quantitative perfusion values.…”