Detection and characterization of urinary stones using material-specific images derived from contrast-enhanced dual-energy CT urography

OBJECTIVE

To determine the accuracy of material-specific images derived from contrast-enhanced dual-energy CT urography (DECTU) in detecting and measuring urinary stones in comparison with that of unenhanced images and its utility in calcified stone differentiation.

METHODS

105 patients with 202 urinary stones (121 had confirmed composition by infrared spectroscopy) underwent triphasic (unenhanced, portal venous (VP) and excretory phase (EP)) DECTU. Material-specific images were derived in VP and EP with calcium-water, calcium-iodine and CaOxalate_Dihydrate (COD)-Hydroxyapatite (HAP) as basis material pairs. Stone number and size were recorded on unenhanced images and VP and EP material-specific images, where stone densities were also measured. Material densities of calcified stones (pure calcium oxalate [pCaO, n = 34], mixed calcium oxalate [mCaO, n = 14], mixed carbonate phosphate [mCaP, n = 70]) were compared and thresholds for differentiating these stones were determined using receiver operating characteristic analysis.

RESULTS

All 202 urinary stones were detected on the unenhanced, calcium (water) and calcium (iodine) images in VP. While the detection rate was significantly decreased to 58 and 64% using calcium (water) and calcium (iodine) images in EP, respectively (all p < 0.001). Stone sizes measured on calcium (iodine) images in VP was similar to that of unenhanced images (10.6 vs 10.7 mm, p > 0.05). Significant differences in material densities were found among pCaO, mCaO and mCaP on COD(HAP) images with AUC of 0.72-0.74 for differentiating these stones.

CONCLUSION

Material-specific images in VP derived from DECTU allow reliably detecting and measuring urinary tract stones in comparison with unenhanced images and can identify calcified stones with moderate diagnostic performance to provide potential 33% dose reduction.

ADVANCES IN KNOWLEDGE

Material-specific images, especially the calcium (iodine) images in VP allow for reliable detection of urinary stones.Stone size measurement should be performed on the calcium (iodine) images in VP.Material density measurements on COD-HAP (VP) material decomposition images can be used to differentiate among pure calcium oxalate, mixed calcium oxalate and mixed carbonate phosphate stones with AUC of 0.72-0.74.

Sensitivity of virtual non-contrast dual-energy CT urogram for detection of urinary calculi: a systematic review and meta-analysis

OBJECTIVE

To determine the sensitivity of dual-energy (DE) virtual non-contrast computed tomography (vNCT), generated from the excretory phase of a CT urogram, compared to true non-contrast CT (tNCT) for the detection of urinary calculi.

METHODS

A search of multiple medical literature databases was performed using predetermined search terms. Inclusion and exclusion criteria were applied, and bias risk was assessed by two independent reviewers using the quality assessment of diagnostic accuracy studies (QUADAS) tool. Collated estimates of sensitivity were generated, and sources of heterogeneity were identified and reviewed.

RESULTS

Thirteen studies (1760 patients; 1740 urinary calculi) were included for sensitivity assessment. Pooled sensitivity for urinary calculi on vNCT was 78.1% (95% CI: 70.2 to 85.0%); however, heterogeneity between studies was very high (I² = 92.0%). Sources of heterogeneity between studies were explored through subgroup analysis by categorising studies according to slice thickness (≥ 2 mm and < 2 mm), use of oral hydration, and use of intravenous furosemide. Pooled sensitivity for detection of urinary calculi on vNCT for studies that used oral hydration and < 2 mm slice thickness was 92.2% (95% CI: 89.5 to 94.5%). Pooled specificity was not performed as true negatives were not reported in most studies. Potential sources of bias were identified in included studies.

CONCLUSION

vNCT demonstrated a moderate pooled sensitivity compared to tNCT for the detection of urinary calculi in split bolus CT urogram protocols. However, subgroup analysis suggests higher sensitivity when employing oral hydration and < 2 mm slice thickness or increment.

KEY POINTS

• vNCT demonstrated moderate pooled sensitivity for the detection of urinary calculi in split bolus CT urogram protocols. • Subgroup analysis suggested higher sensitivity with oral hydration and < 2 mm slice thickness or increment.

Dual-Energy CT applications in urinary tract cancers: an update

Urothelial tumours are the fourth most common cancer in the world and account for the majority of tumours involving the bladder. The symptom that often leads to diagnosis is the presence of haematuria. Diagnosis is made by cystoscopy, which is currently the gold standard in bladder cancer. Computed tomography (CT) performed with pre- and post-contrastographic phases is essential in order to assess the loco-regional and distant extension of disease. The diagnosis and staging of upper tract urothelial cancer (UTUC) are best done with computed tomography urography and flexible ureteroscopy (URS). In the acquisition protocol of this type of tumour, a urographic phase is mandatory, which allows for an accurate diagnostic assessment of the renal pelvis, ureter and bladder, especially in papillary forms. The use of multiple acquisition phases, especially in this type of patient who will have to perform follow-up CTs, leads to the problem of overexposure to ionising radiation, as well as the frequent administration of iodinated contrast medium. For this reason, in recent year, the focus has been put on advanced technologies such as dual-energy CT (DECT), that is a method that can offer some advantages for both radiologist and patient, in the diagnosis of cancer and, in particular, urinary tract disease.

Virtual non-contrast images calculated from dual-energy CT shoulder arthrography improve the detection of intraarticular loose bodies

OBJECTIVE

This study aims to evaluate the image quality of virtual non-contrast (VNC) images calculated from dual-energy CT shoulder arthrography (DECT-A) and their ability to detect periosteal calcifications and intraarticular loose bodies.

MATERIALS AND METHODS

In 129 shoulders of 123 patients, DECT arthrography (80 kV/140 kV) was performed with diluted iodinated contrast material (80 mg/ml). VNC images were calculated with image postprocessing. VNC image quality (1 = worst, 5 = best), dose parameters, and CT numbers (intraarticular iodine, muscle, VNC joint fluid density) were assessed. Image contrast (iodine/muscle) and percentage of iodine removal were calculated. Two independent readers evaluated VNC and DECT-A images for periosteal calcifications and intraarticular loose bodies, and diagnostic confidence (1 = low, 4 = very high) was assessed.

RESULTS

VNC images (129/129) were of good quality (median 4 (3-4)), and the mean effective dose of DECT-A scans was 2.21 mSv (± 1.0 mSv). CT numbers of iodine, muscle, and VNC joint fluid density were mean 1017.6 HU (± 251.6 HU), 64.6 HU (± 8.2 HU), and 85.3 HU (± 39.5 HU), respectively. Image contrast was mean 953.1 HU (± 251 HU) on DECT-A and 31.3 HU (± 32.3 HU) on VNC images. Iodine removal on VNC images was 91% on average. No difference was observed in the detection of periosteal calcifications between VNC (n = 25) and DECT-A images (n = 21) (p = 0.29), while the detection of intraarticular loose bodies was superior on VNC images (14 vs. 7; p = 0.02). Diagnostic confidence was higher on VNC images for both periosteal calcifications (median 3 (3-3) vs. 3 (3-3); p = 0.009) and intraarticular loose bodies (median 3 (3-4) vs. 3 (3-3); p < 0.001).

CONCLUSION

VNC images from DECT shoulder arthrography are superior to DECT-A images for the detection of intraarticular loose bodies and increase the confidence in detecting periosteal calcifications.

Assessment of Diagnostic Yield of Cystoscopy and Computed Tomographic Urography for Urinary Tract Cancers in Patients Evaluated for Microhematuria: A Systematic Review and Meta-analysis

IMPORTANCE

Microhematuria (MH) is a common finding that often leads to further evaluation for urinary tract cancers. There is ongoing debate about the extent to which patients with MH should be evaluated for cancer.

OBJECTIVE

To assess the diagnostic yield for detection of urinary tract cancers, specifically bladder cancer, upper tract urothelial carcinoma (UTUC), and kidney cell carcinoma, among patients evaluated for MH using cystoscopy and computed tomographic (CT) urography.

DATA SOURCES

MEDLINE, Scopus, and Embase were systematically searched for eligible studies published between January 1, 2009, and December 31, 2019.

STUDY SELECTION

Original prospective and retrospective studies reporting the prevalence of cancer among patients evaluated for MH were eligible. Two authors independently screened the titles and abstracts to select studies that met the eligibility criteria and reached consensus about which studies to include. Among 5802 records identified, 5802 articles were screened using titles and abstracts. After exclusions, 55 full-text articles were assessed for eligibility, with 39 studies selected for systematic review.

DATA EXTRACTION AND SYNTHESIS

This systematic review and meta-analysis was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guideline. Studies were quantitatively synthesized using a random-intercept logistic regression model.

MAIN OUTCOMES AND MEASURES

The primary outcome was diagnostic yield, defined as the proportion of patients with a diagnosis of urinary tract cancer (bladder cancer, UTUC, or kidney cell carcinoma) after presentation with MH. Studies were stratified by the percentage of cystoscopy and CT urography use and by high-risk cohorts. The diagnostic yields of CT urography and cystoscopy were calculated for each cancer type.

RESULTS

A total of 30 studies comprising 24 366 patients evaluated for MH were included in the meta-analysis. The pooled diagnostic yield among all patients was 2.00% (95% CI, 1.30%-3.09%) for bladder cancer, 0.02% (95% CI, 0.0%-0.15%) for UTUC, and 0.18% (95% CI, 0.09%-0.36%) for kidney cell carcinoma. Stratification of studies that used cystoscopy and/or CT urography for 95% or more of the cohort produced diagnostic yields of 2.74% (95% CI, 1.81%-4.12%) for bladder cancer, 0.09% (95% CI, 0.01%-0.75%) for UTUC, and 0.10% (95% CI, 0.04%-0.23%) for kidney cell carcinoma. In high-risk cohorts, the diagnostic yields increased to 4.61% (95% CI, 2.34%-8.90%) for bladder cancer and 0.45% (95% CI, 0.22%-0.95%) for UTUC.

CONCLUSIONS AND RELEVANCE

This study's findings suggest that, given the low diagnostic yield of CT urography and the associated risks and costs, limiting its use to high-risk patients older than 50 years is warranted. Risk stratification, as recommended by the recent American Urology Association guidelines on MH, may be a better approach to tailor further evaluation.

Side-by-side evaluation of virtual non-contrast and post-contrast images improves detection of clinically significant urolithiasis on single-phase split bolus dual-energy CT urography

OBJECTIVES

Studies show insufficient sensitivity of virtual non-contrast (VNC) reconstructions for stone detection in dual-energy CT urography (DE-CTU). The aim of this study was to investigate if side-by-side-evaluation of both VNC and post-contrast images could increase the sensitivity of single-phase split bolus DE-CTU.

METHODS

Consecutive patients with haematuria who underwent split bolus DE-CTU on the same dual-source DE-CT scanner were retrospectively enrolled in the study. Intravenous furosemide and oral hydration were employed. Two readers, independently and then jointly in two separate sessions, recorded the location and the longest axial stone diameter on three randomised sets of images: separate VNC and post-contrast images, and side-by-side-reconstructions. True non-contrast (TNC) images served as the standard of reference.

RESULTS

A total of 83 urinary stones were detected on TNC images. Independent reader side-by-side-evaluation of VNC and post-contrast images yielded higher stone detection sensitivity (76 and 84%, respectively) compared to evaluation of only VNC (71 and 81%, respectively) or post-contrast images (64 and 80%, respectively). The sensitivity of joint reader evaluation of side-by-side-images reached almost 86% and was not significantly different from TNC images (p = 0.77). All stones larger than 3 mm were correctly detected by side-by-side-evaluation. Dose reduction of 55% could be achieved by omitting TNC scans.

CONCLUSION

Side-by-side-VNC and post-contrast image evaluation enable detection of clinically significant urolithiasis on single-phase split bolus DE-CTU with significant dose reduction.

ADVANCES IN KNOWLEDGE

This study shows that single-phase DE-CTU is feasible if VNC imaging is simultaneously utilised with post-contrast images.

Diagnostic utility of axial imaging in the evaluation of hematuria: A systematic review and critical appraisal of the literature

INTRODUCTION

Increasing severity of hematuria is instinctively associated with higher likelihood of urological malignancy. However, the robustness of the evidentiary base for this assertion is unclear, particularly as it relates to the likelihood of upper urinary tract pathology. Thus, the value of axial imaging in the diagnostic workup of hematuria is unclear due to differences in the underlying patient populations, raising concern for sampling bias. We performed a systematic review to characterize the literature and association between severity of hematuria and likelihood of upper urinary tract cancer based on axial imaging.

METHODS

MEDLINE, EMBASE, and Cochrane were systematically searched for all studies reporting on adult patients presenting with hematuria. We used Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) for reporting of this systematic review and meta-analysis and the Newcastle-Ottawa Scale for risk of bias assessment. Degree of hematuria was classified as "microscopic," "gross," or "unspecified." Three urological malignancies (bladder, upper tract urothelial, and renal cancer) were considered both individually and in aggregate. Random-effects model with pairwise comparisons was employed to arrive at the axial imaging diagnostic yields.

RESULTS

Twenty-nine studies were included, of which six (20.7%) reported on patients with gross hematuria only, four (13.8%) reported on patients with microscopic hematuria only, seven (24.1%) included both, and 12 (41.4%) did not define or specify the severity of hematuria. Of 29 studies, two (6.9%) were at high-risk of bias, 21 (72.4%) at intermediate-risk, and six (20.7%) at low-risk of bias using the Newcastle-Ottawa criteria. Based on axial imaging, rates of diagnoses of renal, upper tract urothelial, and bladder cancers differed with differing severity of hematuria. Notably, rates of renal and upper tract urothelial carcinoma were higher in studies of patients with unspecified hematuria severity (3.6% and 10.4%, respectively) than among patients with gross hematuria (1.5% and 1.3%, respectively). When all urological malignancies were pooled, patients with unspecified hematuria were diagnosed more frequently (19.5%) compared to those with gross (15.3%) and microscopic hematuria (4.5%, difference=1.51%, 99% confidence interval 3.6-26.5%).

CONCLUSIONS

Lack of granularity in the available literature, particularly with regards to patients with unspecified hematuria severity, limits the generalizability of these results and highlights the need for future studies that provide sufficient baseline information, allowing for firmer conclusions to be drawn.

Split bolus dual-energy CT urography after urine dilution: a one-stop shop for detection and characterisation of urolithiasis

AIM

To determine the diagnostic performance of split-bolus dual-energy computed tomography (CT) urography (SBDECTU) in the detection and characterisation of urolithiasis.

MATERIALS AND METHODS

This single-centre Institute Ethics Committee (IEC)-approved prospective study was conducted from April 2014 to November 2015. One hundred and thirty consenting adults with microscopic haematuria underwent dual-energy true non-enhanced CT (DETNE) of the whole abdomen followed by a SBDECTU. The SBDECTU protocol consisted of synchronous nephrogram-urogram acquisition following urine dilution by oral hydration and normal saline injection. Calculi were detected and characterised using virtual non-enhanced (VNE) images derived from SBDECT were compared with DETNE (the reference standard). The subjective image quality and radiation dose were compared.

RESULTS

Twenty-six participants had one or more calculi (total 129 calculi) detected on DETNE CT. The sensitivity and specificity of VNE on a per-patient basis were 100%. Of the 129 calculi, 118 were detected on VNE, with a sensitivity of 91.47% and an accuracy of 91.47%. Of the calculi, 83.9% (99/118) could be characterised on SBDECTU images. On VNE images, complete iodine subtraction was seen in 73.1% (19/26). By omitting DETNE CT, the mean dose-length product of 537.6±152.9 mGy and volume CT dose index of 10.9±2.9 mGy•cm² could have been saved.

CONCLUSION

SBDECTU has high diagnostic accuracy in the detection and characterisation of clinically significant urinary calculi at potentially half the radiation dose.

Upper urinary tract urothelial carcinoma on multidetector CT: spectrum of disease

Urothelial carcinoma of the upper urinary tract (UUT) is a relatively uncommon genitourinary malignancy, accounting for about 5-7% of urothelial tumors. The significant features of this tumor are multifocality and high rate of recurrence. Computed tomography urography (CTU) has replaced excretory urography (EU) and retrograde pyelography (RP) for imaging of upper tract urothelial carcinoma. While many studies have confirmed high sensitivity (88-100%) and specificity (93-100%) of CTU, an optimized CT protocol is of critical importance in screening, staging, and post-operative follow-up of patients (Chlapoutakis, Eur J Radiol 73(2):334-338, 2010; Caoli and Cohan, Abdom Radiol (NY) 41(6):1100-1107, 2016). The key element of the CT protocol is to have adequate distension of the collecting system with excreted contrast, to detect subtle lesions at an early stage. In this article, we discuss the background of upper urinary tract TTC, pathogenesis, CT protocol and the role of imaging in evaluation of this malignancy, staging, as well as different imaging appearances.

What a difference a delay makes! CT urogram: a pictorial essay

PURPOSE

The aim of this pictorial essay is to demonstrate several cases where the diagnosis would have been difficult or impossible without the excretory phase image of CT urography.

METHODS

A brief discussion of CT urography technique and dose reduction is followed by several cases illustrating the utility of CT urography.

RESULTS

CT urography has become the primary imaging modality for evaluation of hematuria, as well as in the staging and surveillance of urinary tract malignancies. CT urography includes a non-contrast phase and contrast-enhanced nephrographic and excretory (delayed) phases. While the three phases add to the diagnostic ability of CT urography, it also adds potential patient radiation dose. Several techniques including automatic exposure control, iterative reconstruction algorithms, higher noise tolerance, and split-bolus have been successfully used to mitigate dose. The excretory phase is timed such that the excreted contrast opacifies the urinary collecting system and allows for greater detection of filling defects or other abnormalities. Sixteen cases illustrating the utility of excretory phase imaging are reviewed.

CONCLUSIONS

Excretory phase imaging of CT urography can be an essential tool for detecting and appropriately characterizing urinary tract malignancies, renal papillary and medullary abnormalities, CT radiolucent stones, congenital abnormalities, certain chronic inflammatory conditions, and perinephric collections.

Upper and Lower Tract Urothelial Imaging Using Computed Tomography Urography

Computed tomography (CT) urography is the best noninvasive method of evaluating the upper urinary tract for urothelial malignancies. However, the utility of CT urography is heavily contingent on the use of proper image acquisition protocols. This article focuses on the appropriate protocols for optimizing CT urography acquisitions, including contrast administration and the timing of imaging acquisitions, as well as the use of ancillary techniques to increase collecting system distention. In addition, imaging findings are discussed that should raise concern for urothelial carcinoma at each of the 3 segments of the urinary tract: the intrarenal collecting systems, ureters, and bladder.

Dual-Energy Computed Tomography: Dose Reduction, Series Reduction, and Contrast Load Reduction in Dual-Energy Computed Tomography

Evolution in computed tomography technology and image reconstruction have significantly changed practice. Dual energy computed tomography is being increasingly adopted owing to benefits of material separation, quantification, and improved contrast-to-noise ratio. The radiation dose can match that from single energy computed tomography. Spectral information derived from a polychromatic x-ray beam at different energies yields in image reconstructions that reduce the number of phases in a multiphasic examination and decrease the absolute amount of contrast media. This increased analytical and image processing capability provides new avenues for addressing radiation dose and iodine exposure concerns.

Split-bolus single scan CTA for evaluation of mesenteric ischemia

PURPOSE

To evaluate split-bolus single scan CTA protocol for evaluation of acute mesenteric ischemia.

MATERIALS AND METHODS

In this HIPAA-compliant IRB-approved study, consecutive patients evaluated for mesenteric ischemia between 11/2015 and 10/2016 were included. Patients scanned prior to 4/2016 were scanned with multiphasic CTA protocol and after with split-bolus single scan CTA. Objective and subjective evaluation was performed by three board-certified readers. Findings were correlated to composite clinical reference outcome.

RESULTS

Eighty patients were included: 40 with split-bolus and 40 with multiphasic CTA protocol with similar age (60.3 ± 16.2 years vs. 64.7 ± 17.0 years, p = 0.19) and BMI (28.0 ± 6.7 vs. 27.0 ± 8.7, p = 0.56). SMA attenuation was higher in multiphasic protocol compared to split-bolus protocol (336.5 ± 97.5 HU vs. 258.0 ± 67.3 HU, p < 0.001) with similar SMV attenuation (multiphasic 213.7 ± 58.4 HU vs. split-bolus 194.2 ± 52.2 HU, p = 0.14). Optimal phase of bowel, liver, and spleen enhancement was seen in similar high proportion (94-99%) in both protocols. There were 8/40 (20%) positive cases of mesenteric ischemia in each group. There was no difference in the diagnostic confidence of the readers for evaluation of the mesenteric vessels and bowel ischemia. There were no missed cases of mesenteric ischemia in either group. Mean effective dose was 42% lower in the split-bolus group, p < 0.001. There was a higher number of axial images to review in multiphasic protocol compared to split-bolus protocol (437.9 ± 48.7 vs. 263.5 ± 31.2, p < 0.001).

CONCLUSIONS

The split-bolus protocol for evaluation of mesenteric ischemia is clinically feasible with confident and accurate diagnostic ability, while reducing number of images and decreasing radiation exposure to the patient.

Split-Bolus Injection Producing Simultaneous Late Arterial and Portal Venous Phases in CT Enterography: Preliminary Results

OBJECTIVE

The purpose of this article is to evaluate the image quality and added value of split-bolus contrast agent injection combining late arterial and portal venous phases compared with single-bolus contrast agent injection late arterial phase CT enterography.

MATERIALS AND METHODS

Consecutive patients who underwent CT enterography before and after implementation of a single-bolus CT enterography protocol were included. Attenuation and contrast-to-noise ratio (CNR) were assessed by ROI measurements of the bowel wall and arterial and venous structures. Subjective enhancement of the bowel wall (1, arterial; 2, mucosal; 3, transmural; 4, transmural with mucosal hyperenhancement) and bowel abnormalities were assessed by two independent readers. MR enterography examinations, endoscopy reports, and surgery reports within 30 days after CT enterography were used to produce a composite outcome.

RESULTS

Sixty-six patients were included in our study: 33 (mean [± SD] age, 46.0 ± 19.8 years) who underwent split-bolus CT enterography and 33 (mean age, 49.9 ± 19.0 years) who underwent single-bolus CT enterography. Bowel wall attenuation and CNR were higher for split-bolus CT enterography than for single-bolus CT enterography at 120 kVp (enhancement, 98.7 ± 23.1 HU vs 85.1 ± 23.3 HU; CNR, 6.4 ± 2.5 vs 4.4 ± 2.3; p < 0.01). Subjective ratings of bowel wall enhancement were higher with the split-bolus CT enterography than the single-bolus CT enterography (2.6 ± 0.8 vs 2.3 ± 0.6; p < 0.001). Split-bolus CT enterography led to a higher detection rate of mucosal hyperenhancement than did single-bolus CT enterography in patients with active inflammatory bowel disease (100.0% [7/7; 95% CI, 59.0-100.0%] vs 33.3% [2/6; 95% CI, 4.3-77.7%]; p = 0.02), whereas both protocols had a specificity of 100.0% (9/9).

CONCLUSION

Split-bolus CT enterography led to improved CNR (47%) compared with single-bolus CT enterography and significantly increased the detection rate of mucosal hyperenhancement in patients with active inflammatory bowel disease.

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.

Renal applications of dual-energy CT

Dual-energy CT is being increasingly used for abdominal imaging due to its incremental benefit of material characterization without significant increase in radiation dose. Knowledge of the different dual-energy CT acquisition techniques and image processing algorithms is essential to optimize imaging protocols and understand potential limitations while using dual-energy CT renal imaging such as urinary calculi characterization, assessment of renal masses and in CT urography. This review article provides an overview of the current dual-energy CT techniques and use of dual-energy CT in renal imaging.