Feasibility of dose reduction using needle-structured image plates versus powder-structured plates for computed radiography of the knee.

OBJECTIVE

A newly developed computed radiography (CR) detector that uses a storage phosphor plate made of needle-shaped crystals provides improved dose efficiency. The aim of our study was to compare the image quality of standard-dose CR and dose-reduced CR achieved using needle technology for knee imaging in a clinical setting.

MATERIALS AND METHODS

We compared standard CR images obtained using a powder-structured image plate (PIP) (ADC Compact Plus) with images obtained using the new needle-structured image plate (NIP) (DX-S). In 30 consecutive patients with knee pain willing to participate in this study, anteroposterior knee radiographs were acquired with both systems at a standard dose. In addition, NIP images were obtained with approximately 75% and 50% of the standard dose (corresponding incident doses: 300, 235, and 154 μGy, respectively). Images were evaluated in a blinded, side-by-side comparison. Six radiologists determined whether there was an appreciable difference in image quality at five anatomic landmarks in regions with high and low differences of attenuation. They also assessed the delineation of selected abnormalities and ranked them using a 10-point scale. The rating scores were tested for statistical differences using an analysis of variance with repeated measures.

RESULTS

The mean overall rating scores for the evaluation of anatomic landmarks were 6.97 for NIP images obtained at full dose, 6.48 for NIP images obtained at about 75% dose, 5.47 for NIP images obtained at half dose, and 6.01 for PIP images. There was a significant difference in favor of the CR system with an NIP at the same dose level (p < 0.05). The NIP images obtained at a dose of about 75% were also ranked significantly better than the PIP images with regard to the depiction of both anatomic landmarks and abnormalities. The readers ranked half-dose NIP images inferior to the PIP images with regard to abnormalities and anatomic landmarks in areas with high attenuation, whereas in areas with low attenuation, the image quality was regarded as equivalent to the standard technique.

CONCLUSION

NIP technology allows a dose reduction of approximately 25% compared with PIP while still providing higher image quality. Even at the half-dose level, there was no relevant loss of image quality with regard to the delineation of anatomic landmarks in areas with low attenuation in anteroposterior knee images. The higher dose efficiency of the needle-detector CR technology compared with conventional CR can be used either for dose reduction or for improved image quality.