Proceedings Article | 9 March 2017
KEYWORDS: X-rays, Spatial frequencies, Angiography, Sensors, Modulation transfer functions, Scintillators, Quantum efficiency, Prototyping, Sensor performance, Diagnostics, Image resolution, X-ray detectors, CMOS sensors
X-ray detectors to meet the high-resolution requirements for endovascular image-guided interventions (EIGIs)
are being developed and evaluated. A new 49.5-micron pixel prototype detector is being investigated and
compared to the current suite of high-resolution fluoroscopic (HRF) detectors. This detector featuring
a 300-micron thick CsI(Tl) scintillator, and low electronic noise CMOS readout is designated the HRF-
CMOS50. To compare the abilities of this detector with other existing high resolution detectors, a standard
performance metric analysis was applied, including the determination of the modulation transfer function
(MTF), noise power spectra (NPS), noise equivalent quanta (NEQ), and detective quantum efficiency (DQE)
for a range of energies and exposure levels. The advantage of the smaller pixel size and reduced blurring due
to the thin phosphor was exemplified when the MTF of the HRF-CMOS50 was compared to the other high
resolution detectors, which utilize larger pixels, other optical designs or thicker scintillators. However, the
thinner scintillator has the disadvantage of a lower quantum detective efficiency (QDE) for higher diagnostic
x-ray energies. The performance of the detector as part of an imaging chain was examined by employing
the generalized metrics GMTF, GNEQ, and GDQE, taking standard focal spot size and clinical imaging
parameters into consideration. As expected, the disparaging effects of focal spot unsharpness, exacerbated by
increasing magnification, degraded the higher-frequency performance of the HRF-CMOS50, while increasing
scatter fraction diminished low-frequency performance. Nevertheless, the HRF-CMOS50 brings improved
resolution capabilities for EIGIs, but would require increased sensitivity and dynamic range for future clinical
application.
