Focused Dual-energy CT Maintains Diagnostic and Compositional Accuracy for Urolithiasis Using Ultralow-dose Noncontrast CT

Dual-energy CT kidney stone characterization-can diagnostic accuracy be achieved at low radiation dose?

OBJECTIVES

To assess the accuracy of low-dose dual-energy computed tomography (DECT) to differentiate uric acid from non-uric acid kidney stones in two generations of dual-source DECT with stone composition analysis as the reference standard.

METHODS

Patients who received a low-dose unenhanced DECT for the detection or follow-up of urolithiasis and stone extraction with stone composition analysis between January 2020 and January 2022 were retrospectively included. Collected stones were characterized using X-ray diffraction. Size, volume, CT attenuation, and stone characterization were assessed using DECT post-processing software. Characterization as uric acid or non-uric acid stones was compared to stone composition analysis as the reference standard. Sensitivity, specificity, and accuracy of stone classification were computed. Dose length product (DLP) and effective dose served as radiation dose estimates.

RESULTS

A total of 227 stones in 203 patients were analyzed. Stone composition analysis identified 15 uric acid and 212 non-uric acid stones. Mean size and volume were 4.7 mm × 2.8 mm and 114 mm3, respectively. CT attenuation of uric acid stones was significantly lower as compared to non-uric acid stones (p < 0.001). Two hundred twenty-five of 227 kidney stones were correctly classified by DECT. Pooled sensitivity, specificity, and accuracy were 1.0 (95%CI: 0.97, 1.00), 0.93 (95%CI: 0.68, 1.00), and 0.99 (95%CI: 0.97, 1.00), respectively. Eighty-two of 84 stones with a diameter of  ≤ 3 mm were correctly classified. Mean DLP was 162 ± 57 mGy*cm and effective dose was 2.43 ± 0.86 mSv.

CONCLUSIONS

Low-dose dual-source DECT demonstrated high accuracy to discriminate uric acid from non-uric acid stones even at small stone sizes.

KEY POINTS

• Two hundred twenty-five of 227 stones were correctly classified as uric acid vs. non-uric acid stones by low-dose dual-energy CT with stone composition analysis as the reference standard. • Pooled sensitivity, specificity, and accuracy for stone characterization were 1.0, 0.93, and 0.99, respectively. • Low-dose dual-energy CT for stone characterization was feasible in the majority of small stones  < 3 mm.

Comparison of Four Dual-Energy CT Scanner Technologies for Determining Renal Stone Composition: A Phantom Approach

Background Studies have investigated the value of various dual-energy CT (DECT) technologies for determining renal stone composition. However, sparse multivendor comparison data exist. Purpose To compare the performance of four DECT technologies in determining renal stone composition at standard- and low-dose acquisitions. Materials and Methods This was an in vitro phantom study. Seventy-one urinary stones (size: 2.7-14.1 mm) of known chemical composition (51 calcium, four struvite, four cystine, and 12 urate) were placed in a custom-made cylindrical phantom. Consecutive scans with manufacturer-recommended protocols and dose-optimized institutional protocols (up to 80% reduction in volumetric CT dose index) were obtained with rapid kilovolt peak switching DECT (rsDECT) (n = 2), dual-source DECT (n = 2), twin-beam DECT (tbDECT) (n = 1), and dual-layer detector-based CT (dlDECT) (n = 1) scanners. The image data sets were analyzed using effective atomic number and dual-energy ratio indexes of maximally available and comparable spectra. The performance of each combination of scanner technology, method, and acquisition was assessed. Logistic regression models were used to calculate the area under the receiver operating characteristic curve (AUC). Results After image analysis, all scanners except tbDECT had an AUC greater than 0.95 in at least one acquisition in distinguishing urate from other stones. All DECT techniques were able to help differentiate calcium oxalate monohydrate stones with moderate accuracy (AUC: 0.70-0.83), and brushite was differentiated from urate with AUC greater than 0.99. There was no correlation between performance and acquisition with dose-optimized and/or vendor-recommended settings. Conclusion All four dual-energy CT (DECT) technologies enabled accurate determination of stone composition at standard- and low-dose acquisitions; however, performance varied based on the scanner parameters, DECT technique, and stone type. © RSNA, 2022 Online supplemental material is available for this article. See also the editorial by Ringl and Apfaltrer in this issue.

Can Dual Energy CT with Fast kV-Switching Determine Renal Stone Composition Accurately?

RATIONALE AND OBJECTIVES

To determine whether a single source computed tomography (CT) system utilizing fast kV switching and low dose settings can characterize (diameter and chemical composition) renal stones accurately when compared infrared spectroscopy.

MATERIALS AND METHODS

The chemical composition of 15 renal stones was determined using Fourier transform infrared spectroscopy. The stones were inserted into a porcine kidney and placed within a water tank for CT scanning using both fast kV switching dual energy and standard protocols. Effective atomic number of each stone was measured using scanner software. Stone diameter measurements were repeated twice to determine intra-rater variation and compared to actual stone diameter as measured by micro CT.

RESULTS

The chemical composition of three stones (one calcium phosphate and two carbonite apatite) could not be determined using the scanner software. The composition of 10/12 remaining stones was correctly identified using dual energy computed tomography (83% absolute agreement; k = 0.69). No statistical difference (p = 0.051) was noted in the mean stone diameter as measured by clinical CT and micro CT.

CONCLUSION

Dual energy computed tomography using fast kV switching may potentially be developed as a low dose clinical tool for identifying and classifying renal stones in vivo supporting clinical decision-making.

Single-energy CT predicts uric acid stones with accuracy comparable to dual-energy CT-prospective validation of a quantitative method

OBJECTIVES

To prospectively validate three quantitative single-energy CT (SE-CT) methods for classifying uric acid (UA) and non-uric acid (non-UA) stones.

METHODS

Between September 2018 and September 2019, 116 study participants were prospectively included in the study if they had at least one 3-20-mm urinary stone on an initial urinary tract SE-CT scan. An additional dual-energy CT (DE-CT) scan was performed, limited to the stone of interest. Additionally, to include a sufficient number of UA stones, eight participants with confirmed UA stone on DE-CT were retrospectively included. The SE-CT stone features used in the prediction models were (1) maximum attenuation (maxHU) and (2) the peak point Laplacian (ppLapl) calculated at the position in the stone with maxHU. Two prediction models were previously published methods (ppLapl-maxHU and maxHU) and the third was derived from the previous results based on the k-nearest neighbors (kNN) algorithm (kNN-ppLapl-maxHU). The three methods were evaluated on this new independent stone dataset. The reference standard was the CT vendor's DE-CT application for kidney stones.

RESULTS

Altogether 124 participants (59 ± 14 years, 91 men) with 106 non-UA and 37 UA stones were evaluated. For classification of UA and non-UA stones, the sensitivity, specificity, and accuracy were 100% (37/37), 97% (103/106), and 98% (140/143), respectively, for kNN-ppLapl-maxHU; 95% (35/37), 98% (104/106), and 97% (139/143) for ppLapl-maxHU; and 92% (34/37), 94% (100/106), and 94% (134/143) for maxHU.

CONCLUSION

A quantitative SE-CT method (kNN-ppLapl-maxHU) can classify UA stones with accuracy comparable to DE-CT.

KEY POINTS

• Single-energy CT is the first-line diagnostic tool for suspected renal colic. • A single-energy CT method based on the internal urinary stone attenuation distribution can classify urinary stones into uric acid and non-uric acid stones with high accuracy. • This immensely increases the availability of in vivo stone analysis.

Dose independent characterization of renal stones by means of dual energy computed tomography and machine learning: an ex-vivo study

OBJECTIVES

To predict the main component of pure and mixed kidney stones using dual-energy computed tomography and machine learning.

METHODS

200 kidney stones with a known composition as determined by infrared spectroscopy were examined using a non-anthropomorphic phantom on a spectral detector computed tomography scanner. Stones were of either pure (monocrystalline, n = 116) or compound (dicrystalline, n = 84) composition. Image acquisition was repeated twice using both, normal and low-dose protocols, respectively (ND/LD). Conventional images and low and high keV virtual monoenergetic images were reconstructed. Stones were semi-automatically segmented. A shallow neural network was trained using data from ND1 acquisition split into training (70%), testing (15%) and validation-datasets (15%). Performance for ND2 and both LD acquisitions was tested. Accuracy on a per-voxel and a per-stone basis was calculated.

RESULTS

Main components were: Whewellite (n = 80), weddellite (n = 21), Ca-phosphate (n = 39), cysteine (n = 20), struvite (n = 13), uric acid (n = 18) and xanthine stones (n = 9). Stone size ranged from 3 to 18 mm. Overall accuracy for predicting the main component on a per-voxel basis attained by ND testing dataset was 91.1%. On independently tested acquisitions, accuracy was 87.1-90.4%.

CONCLUSIONS

Even in compound stones, the main component can be reliably determined using dual energy CT and machine learning, irrespective of dose protocol.

KEY POINTS

• Spectral Detector Dual Energy CT and Machine Learning allow for an accurate prediction of stone composition. • Ex-vivo study demonstrates the dose independent assessment of pure and compound stones. • Lowest accuracy is reported for compound stones with struvite as main component.

Aktualisierung der S2k-Leitlinie zur Diagnostik, Therapie und Metaphylaxe der Urolithiasis (AWMF Registernummer 043-025)

Die Zunahme des medizinischen Wissens, technische Neuerungen gemeinsam mit demographischem Wandel stellen eine Herausforderung an die Neukonzeption von Leitlinien und klinischen Studien dar. Die vorliegende S2k-Leitlinie, die sich ausschließlich mit Nieren- und Harnleitersteinen beschäftigt, soll die Behandlung von Harnsteinpatienten in Klinik und Praxis unterstützen, aber auch Patienteninformationen zur Urolithiasis geben. Die zunehmende interdisziplinäre Zusammenarbeit in der Steintherapie zeigt sich auch an der Anzahl beteiligter Fachgruppen und Arbeitsgemeinschaften in der Erstellung des neuen Leitlinienupdates. Die vorliegende, aus einem interdisziplinären Konsensusprozess hervorgegangene S2k-Leitlinie stellt die aktuellen Empfehlungen praxisnah dar und gibt Entscheidungshilfen für Diagnostik‑, Therapie- und Metaphylaxemaßnahmen auf Basis von Expertenmeinungen und verfügbaren Evidenzgrundlagen aus der Literatur.

Percutaneous kidney stone surgery and radiation exposure: A review

During the past 3 decades, radiation exposure (RE) has increased drastically among patients undergoing percutaneous nephrolithotomy (PCNL), thus potentially causing new cases of cancer each year. The effective dose received by patients comes from pre- and post-operative computed tomography (CT) and intraoperative fluoroscopy (FL). We reviewed literature to find novel techniques and approaches that help to decrease RE of patients and personnel. We performed PubMed search using keywords percutaneous nephrolithotomy, intraoperative fluoroscopy, radiation exposure, imaging, percutaneous access, ultrasound, computed tomography, endoscopy, reconstruction, innovations, and augmented reality. Forty-four relevant articles were included in this review. As much as 20% of patients with first diagnosed urolithiasis exceed background RE level almost 17-fold. For diagnosing purposes using low-dose and ultra-low-dose CT, as well as low-dose dual energy scan protocols can be efficient ways to decrease RE while maintaining decent accuracy. Patients with urinary stones can be effectively monitored with digital tomosynthesis, ultrasound alone or ultrasound combined with plain film of the abdomen. Percutaneous access (PCA) into the kidney can be performed with reduced or even no RE, using novel PCA methods. REs from conventional imaging techniques during diagnosis and treatment increase probability of non-stochastic radiation effects. Urologists should be aware of protocols that decrease RE from CT and FL in diagnosis and management of urinary stones. Consideration of recently developed imaging modalities and PCA techniques will also aid in adherence to the “as low as reasonably achievable” principle.

New Imaging Techniques in the Management of Stone Disease

Recent advances in computed tomography, X-ray-based imaging, and ultrasonography have improved the accuracy of urinary stone detection and differentiation of stone composition while minimizing radiation exposure. Dual-energy computed tomography and digital tomosynthesis show promise in predicting mineral composition to optimize medical and surgical therapy. Electromagnetic tracking may enhance the use of ultrasonography to achieve percutaneous renal access for nephrolithotomy. This article reviews innovations in imaging technology in the contemporary management of urinary stone disease.

Predictors of Uric Acid Stones: Mean Stone Density, Stone Heterogeneity Index, and Variation Coefficient of Stone Density by Single-Energy Non-Contrast Computed Tomography and Urinary pH

We analyzed the capacities of pertinent parameters (determined by single-energy non-contrast computed tomography [NCCT]) and urinary pH to predict uric acid stones. We reviewed the medical records of 501 patients whose stones were removed surgically or passed spontaneously between December 2014 and April 2016. Qualifying participants (n = 420) were stratified by the nature of the stone (calcium oxalate, uric acid, or infectious). Based on NCCT, we determined maximal stone length (MSL), mean stone density (MSD), and stone heterogeneity index (SHI) using Hounsfield units (HU) and calculated the variant coefficient of stone density (VCSD = SHI/MSD × 100). Urinary pH was also ascertained. Mean patient age was 55.55 ± 15.46 years. MSD (448.59 ± 173.21 HU), SHI (100.81 ± 77.37 HU), and VCSD (22.58 ± 10.55) proved to be significantly lower in uric acid versus other types of stones, as did urinary pH (5.33 ± 0.56; all p < 0.001). Receiver operating characteristic (ROC) curves depicting predictability of uric acid stones yielded area under ROC curve (AUC) values for MSD, SHI, VCSD, and urinary pH of 0.806 (95% CI: 0.761⁻0.850), 0.893 (95% CI: 0.855⁻0.931), 0.782 (95% CI: 0.726⁻0.839), and 0.797 (95% CI: 0.749⁻0.846), respectively, with corresponding cutpoints of 572.3 HU, 140.4 HU, 25.79, and 6.0. Among these four parameters, SHI was verifiably (DeLong's test) the most effective predictor of uric acid stones (all p < 0.001). Compared with MSD, VCSD, and urinary pH, SHI may better predict uric acid stones, using a cutpoint of 140.4 HU.

A new method for predicting uric acid composition in urinary stones using routine single-energy CT

Urinary stones composed of uric acid can be treated medically. Prediction of uric acid stone type is, therefore, desirable when a urinary stone is diagnosed with unenhanced CT. The purpose of the present study was to describe single-energy thin slice quantitative CT parameters of urinary stones correlated to chemical stone type and to develop a method to distinguish pure uric acid stones (UA) from other stones (non-UA/Mix). Unenhanced thin slice single-energy CT images of 126 urinary stones (117 patients) with known chemical stone type were retrospectively included in the study. Among the included stones, 22 were UA and 104 were non-UA/Mix. The included CT images and Laplacian filtered images of the stones were quantitatively analyzed using operator-independent methods. A post hoc classification method for pure UA stones was created using a combination of cutoff values for the peak attenuation and peak point Laplacian. The stone types differed in most quantitative image characteristics including mean attenuation (p < 0.001), peak attenuation (p < 0.001), and peak point Laplacian (p < 0.001). The sensitivity for the post hoc-developed peak attenuation-peak point Laplacian method for classifying pure UA stones was 95% [21/22, 95% CI (77-100%)] and the specificity was 99% [103/104, 95% CI (95-100%)]. In conclusion, quantitative image analysis of thin slice routine single-energy CT images is promising for predicting pure UA content in urinary stones, with results comparable to double energy methods.

Dual-energy computed tomography for characterizing urinary calcified calculi and uric acid calculi: A meta-analysis

OBJECTIVE

A meta-analysis was conducted to determine the accuracy of dual-energy computed tomography (DECT) for differentiating urinary uric acid and calcified calculi.

METHODS

The databases PubMed, EMBASE, Web of Science, and the Cochrane Library were searched up to May 2016 for relevant original studies. Data were extracted to calculate the pooled sensitivity, specificity, diagnostic odds ratio (OR), positive and negative likelihood ratios (PLR and NLR), and areas under summary receiver operating characteristic (AUROC) curves for analysis.

RESULTS

Nine studies (609 stones in 415 patients) were included. For differentiating uric acid (UA) and non-UA calculi with DECT, the analysis indicated: pooled weighted sensitivity, 0.955 (95% CI, 0.888-0.987); specificity, 0.985 (95% CI, 0.970-0.993); PLR, 0.084 (95% CI, 0.041-0.170); NLR 33.327 (95% CI, 18.516-59.985); and diagnostic OR 538.18 (95% CI, 195.50-1478.5). The AUROC value was 0.9901. For calcified stones, the analysis indicated: pooled weighted sensitivity, 0.994 (95% CI, 0.969-1); specificity, 0.973 (95% CI, 0.906-0.997); PLR, 11.200 (95% CI, 4.922-25.486); NLR 0.027 (95% CI, 0.010-0.072); and diagnostic OR 654.89 (95% CI, 151.31-2834.4). The AUROC value was 0.9915.

CONCLUSION

This meta-analysis found that DECT is a highly accurate noninvasive method for characterizing urinary uric acid and calcified calculi.

Imaging of flank pain: readdressing state-of-the-art

Pain resulting from renal and ureteral stones is a common cause for patients presenting in the acute setting. Since the late 1990s, computed tomography (CT) has been the initial imaging method of choice to evaluate patients with suspected ureteral stones; however, concerns regarding both radiation dose and cost-effectiveness have prompted investigations into a different imaging algorithm. Studies utilizing ultrasound have provided evidence indicating that it may be a more appropriate first step, with selective use of CT in selected cases, in the diagnostic work-up. Techniques have evolved with low-dose CT, dual-energy CT, and magnetic resonance urography emerging as useful in imaging of renal colic patients. This manuscript reviews the current literature on state-of-the-art imaging for acute flank pain and proposes a new imaging algorithm in the evaluation of patients with acute flank pain and suspected ureteral stones.

Acute vertebral fracture after spinal fusion: a case report illustrating the added value of single-source dual-energy computed tomography to magnetic resonance imaging in a patient with spinal Instrumentation

Magnetic resonance imaging (MRI) is degraded by metal-implant-induced artifacts when used for the diagnostic assessment of vertebral compression fractures in patients with instrumented spinal fusion. Dual-energy computed tomography (DECT) offers a promising supplementary imaging tool in these patients. This case report describes an 85-year-old woman who presented with a suspected acute vertebral fracture after long posterior lumbar interbody fusion. This is the first report of a vertebral fracture that showed bone marrow edema on DECT; however, edema was missed by an MRI STIR sequence owing to metal artifacts. Bone marrow assessment using DECT is less susceptible to metal artifacts than MRI, resulting in improved visualization of vertebral edema in the vicinity of fused vertebral bodies.