Image Quality and Patient-Specific Organ Doses in Stone Protocol CT: A Comparison of Traditional CT to Low Dose CT with Iterative Reconstruction

Abstract

Objective To compare organ specific radiation dose and image quality in kidney stone patients scanned with standard CT reconstructed with filtered back projection (FBP-CT) to those scanned with low dose CT reconstructed with iterative techniques (IR-CT). Materials and Methods Over a one-year study period, adult kidney stone patients were retrospectively netted to capture the use of noncontrasted, stone protocol CT in one of six institutional scanners (four FBP and two IR). To limit potential CT-unit use bias, scans were included only from days when all six scanners were functioning. Organ dose was calculated using volumetric CT dose index and patient effective body diameter through validated conversion equations derived from previous cadaveric, dosimetry studies. Board-certified radiologists, blinded to CT algorithm type, assessed stone characteristics, study noise, and image quality of both techniques. Results FBP-CT (n=250) and IR-CT (n=90) groups were similar in regard to gender, race, body mass index (mean BMI = 30.3), and stone burden detected (mean size 5.4 ± 1.2 mm). Mean organ-specific dose (OSD) was 54-62% lower across all organs for IR-CT compared to FBP-CT with particularly reduced doses (up to 4.6-fold) noted in patients with normal BMI range. No differences were noted in radiological assessment of image quality or noise between the cohorts, and intrarater agreement was highly correlated for noise (AC2=0.873) and quality (AC2=0.874) between blinded radiologists. Conclusions Image quality and stone burden assessment were maintained between standard FBP and low dose IR groups, but IR-CT decreased mean OSD by 50%. Both urologists and radiologists should advocate for low dose CT, utilizing reconstructive protocols like IR, to reduce radiation exposure in their stone formers who undergo multiple CTs.

Ultra-Low-Dose CT: An Effective Follow-Up Imaging Modality for Ureterolithiasis

“…8,9 Low-dose scans have been shown to have 59% lower organ-specific radiation compared with standard CT with no loss of image quality. 5,10 More recently, ultra-low-dose CT (ULD CT) protocols, which use even less ionizing radiation than lowdose CT, have been developed. A systematic review demonstrated that ULD CT (<1.9 mSv) and low-dose CT (<3.5 mSv) have comparable sensitivity (90%-96%) and specificity (97%-99%) for ureteral stones.…”

Comparison of diagnostic accuracy of ultra low‐dose computed tomography and X‐ray of the kidneys, ureters and bladder for urolithiasis in the follow‐up setting

“…12,22 The long-term risks of high radiation exposure become a concern in those patients undergoing repeated CTs for recurrent urolithiasis, particularly with regard to the development of secondary malignancy. 8,23 Furthermore, CT examinations are being performed more frequently as imaging services become increasingly accessible. 24 LD-CTKUB protocols for urolithiasis have been investigated in several studies, with several having an effective dose of <2.0 mSv.…”

“…Ongoing follow up forms an important component of its management with CT imaging being the established, gold‐standard approach 12,22 . The long‐term risks of high radiation exposure become a concern in those patients undergoing repeated CTs for recurrent urolithiasis, particularly with regard to the development of secondary malignancy 8,23 . Furthermore, CT examinations are being performed more frequently as imaging services become increasingly accessible 24 …”

The Diagnostic Accuracy of Low-Dose Computed Tomography in Diagnosing Urolithiasis: A Systematic Review and Meta-Analysis

“…Time has witnessed the development of the reconstruction algorithms during these years. Conventional ltered back projection (FBP) reconstruction technique has been well received due to its quick imaging technology for decades [36]. Iterative reconstruction (IR) algorithms have been introduced to improve image quality with less image noise [37][38].…”