Low-dose Non-contrast CT Research Articles

Determining the composition of urinary tract calculi using stone-targeted dual-energy CT: evaluation of a low-dose scanning protocol in a clinical environment.

This study will evaluate the accuracy of dual-energy CT (DECT) in characterizing urinary tract stone composition on patients presenting to a UK hospital with renal colic. The study will also assess the additional radiation dose burden of DECT over standard protocol. Data from 106 DECTs between October 2011 and October 2015 were retrospectively analyzed. Patients were imaged using a Toshiba Aquilion ONE™ CT scanner (Toshiba Medical Systems, Otawara-shi, Japan). All patients received a low-dose non-contrast CT of the abdomen and pelvis prior to stone-targeted DECT at 80 and 135 kVp and 40-mm field of view. Radiation dose output was evaluated using dose-length product (DLP). 19 stones were recovered and their compositions were analyzed using Fourier transform infrared spectroscopy. 137 stones were characterized. Mean stone diameter was 8.8 mm (range 3-48 mm). There was an 18.7% increase in mean DLP for DECT over standard CT protocol (319.4 vs 269.1 mGy cm; p < 0.001). Infrared spectroscopy analysis of 19 recovered stones identified 15 stones as calcium, 2 stones as cystine and 2 stones as mixed composition. Dual energy correctly predicted 11 (78.6%) of 14 calcium stones, 2 (100%) of 2 mixed composition stones and 0 (0%) of 2 cystine stones, resulting in a fair agreement (Cohen's κ = 0.374, p = 0.009). DECT is able to determine the composition of urinary tract stones with fair accuracy. Its utility is offset by a small but significant supplementary radiation exposure. Advances in knowledge: DECT can provide urological surgeons with useful diagnostic stone material information prior to planning optimal management of stone disease.

Validation of Low Dose Non-contrast CT Scanning and Ultrasound Scanning as a Screening Tool for Abdominal Aortic Aneurysms – A Substudy from the DANCAVAS Trial

Objective: Establishing non-contrast-enhanced Computed Tomography (CT), as equal and/or superior to the current abdominal aortic aneurysm (AAA) screening standard e Ultrasound Sonography (US). Material: 538 consecutive attending men to the pilot study of the randomized Danish CardioVascular Screening trial (DANCAVAS trial). Method: Participants underwent non-contrast CT and US examination. Measurements were done outer-to-outer in both transverse and anterior-posterior (AP) axial plane. All were done in systolic phase. Abdominal aortic aneurysms were defined as a maximal infrarenal aortic diameter of 30 mm or more. Sensitivity and specificity were calculated using CT and US as the golden standard, respectively. All measurements were tested for correlation and variance in diameters. Differences in means were tested using the paired t-test. Results: Of the 529 men examined, 30 AAAs were found by CT, giving a prevalence of 5.7%. However, US failed to detect 9 of these, resulting in a sensitivity of 70%. US specificity was 99%. Thus US based AAA prevalence was 4.0%. CT tested against US; sensitivity overall was 87.5% with a specificity of 98.2%. Analysis of paired differences showed no significance between CT and US, with means varying only slightly in both axial measurements. Measurements made in both the AP and transverse plane showed general agreement between the modalities with no tendency to increasing variance with increasing diameters. Conclusions: In a multifaceted screening program for CVD, CT appears superior to US. In addition to detecting the AAA otherwise detectable by US, the CT scanning enables a more thorough evaluation by providing visualization of unknown lesions of the coronary vessels, thoracic aorta and the iliac arteries. In fact, some isolated iliac aneurysms were detected by CT and not US. In addition, the US based prevalence on Fyen (2014) is almost similar to the prevalence of 4.2% detected in the Viborg County (1994e98), and higher than the prevalence of 3.3% detected in the VIVA trial (2008e11) in the Mid region of Denmark Median Arcuate Ligament Syndrome Qasam M. Ghulam , Kim K. Bredahl , Thomas Axelsen , Torben V. . Schroeder , Lisbeth E. Hvolris , Viggo B. Kristiansen , Svend Schulze , Lisbeth G. Jorgensen , Jonas P. Eiberg a,e a Clinic of Vascular Surgery, Rigshospitalet, Blegdamsvej 9, 2100 Copenhagen, Denmark b Department of Radiology, Rigshospitalet, Blegdamsvej 9, 2100 Copenhagen, Denmark c Center for Clinical Education, Center for HR, Region H, Blegdamsvej 9, 2100 Copenhagen, Denmark d Department of Gastro-Surgery, Hvidovre Hospital, Kettegard Alle 30, 2650 Hvidovre, Denmark e University of Copenhagen, Blegdamsvej 9, 2100 Copenhagen, Denmark Abstract The median arcuate ligament syndrome (MALS) is a rare entityThe median arcuate ligament syndrome (MALS) is a rare entity and poorly described in the Danish literature, which makes the exact prevalence difficult to estimate. It is more often among women, typically younger and less cardiovascular stigmatized as compared to the usual patients suffering intestinal ischemia. It is believed that the median arcuate ligament (MAL), being a fibrous structure of the diaphragm, compresses the celiac trunk, causing a stenosis and the characteristic “hook-shape” found on imaging. Whether symptoms originate from malperfusion of the gastrointestinal organs or are caused by compression of sympathetic fibers is not fully elucidated. The syndrome is characterized by chronic abdominal pain, postprandiale pain and weight loss. Moreover, worsening of abdominal pain associated with physical activity and when lying supine is commonly described. Most centers are reluctant to perform percutaneous transluminal angioplasty (PTA), because of the significant risk of stent-fracture and failure, as well as open ligament release and revascularization due to the extensive nature of such a procedure. Within the last decade, laparoscopic approacheswith release of themedian arcuate ligament have shown promising results and few periand postoperative complications. In some cases with insufficient symptom relief after ligament relief, a postoperative PTA can be performed adjunctively without the risk of stent-fracture. Median arcuate ligament syndrome is a rare disease, and should be a diagnosis of

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We thank for these pleasant comments and are happy that the idea of dose-reduced computed tomography (CT) and CT-based compositional analysis of urinary stones is of importance for the editors of Urology. 1 Slater R.C. Jackman S.V. Focused dual-energy CT maintains diagnostic and compositional accuracy for urolithiasis using ultralow-dose noncontrast CT [Editorial Comment]. Urology. 2015; 86: 1097-1103 Abstract Full Text Full Text PDF PubMed Google Scholar New developments of imaging modalities have influenced different fields of medicine sustainably, including urolithiasis management. In many urology departments, CT has replaced radiography of kidney, ureter, and bladder as well as intravenous pyelogram almost completely in primary evaluation of renal colic patients. Over the years, the CT technology could be improved significantly due to bringing innovations such as dose-reduced protocols, shorter examination times, high-definition imaging, and in situ compositional analysis of the targeted stones. Our study was performed on 61 patients revealing high sensitivity and specificity in detection of clinically relevant uric acid- and non–uric acid-containing fragments. 1.We believe that similar results for sensitivity and specificity rates can be reproduced in other institutions using the highly dose-reduced noncontrast CT (NCCT) protocol including compositional analysis. The methods applied have been described in detail. We would be very pleased if other groups, wishing to decrease radiation exposure of urolithiasis patients, would join our efforts and work on related topics in collaborative projects. 2.In the German health care system, the radiologist is involved in the evaluation process of the CT results and decision making whether the dual-energy (DE) technology is applied. Because of this organization model, a significant decrease in radiation can be achieved. We are aware that this is not the case in many countries worldwide. As a consequence, this might be the crucial limitation in the acceptance of this approach in differently organized health care systems, where CT scans are not interpreted directly by a radiologist and the image acquisition is performed independently by excellently trained radiology technicians. We believe that diagnosing urolithiasis might be feasible for such personnel after professional training. Furthermore, these measures would make radiology technicians more familiar with the DE technology and novel CT protocols. In our opinion, the decision whether to use a targeted DE mode scan can also be taken by a radiology technician. In countries where legal issues prohibit such course of action, efforts should be undertaken to rearrange the workflow in radiology departments and establish a timely involvement of a radiologist in the CT scan evaluation in stone patients. 3.Conventional NCCT might provide reliable information regarding stone composition based on Hounsfield unit characteristics of a visualized fragment. However, this might not be accurate in many cases and leads to substantially higher patient radiation exposure. To our knowledge, it is not possible to determine the stone composition correctly while performing an NCCT according to an ultralow energy dose protocol. Therefore, an additional DE technology–based analysis has to be implemented. Applying our novel protocol, low-dose NCCT plus DE mode–based analysis of stone composition results in significantly lower cumulative radiation exposure and provides superior results at the same time. “Primum non nocere” (first, do no harm): We believe that this justifies potentially higher financial expenses and time. Editorial CommentUrologyVol. 86Issue 6PreviewThe authors provide a timely demonstration of an innovative low-dose noncontrast computed tomography (NCCT) plus dual-energy CT (DECT) protocol in reducing radiation exposure in the evaluation of patients presenting with urolithiasis while simultaneously maintaining accurate compositional analysis of such calculi.1 This protocol calls for patients to undergo an ultralow-dose NCCT followed by a focused dose-reduced noncontrast DECT. It was evaluated in 61 patients whose stones were available for chemical analysis. Full-Text PDF

Non-contrast CT at comparable dose to an abdominal radiograph in patients with acute renal colic; impact of iterative reconstruction on image quality and diagnostic performance

ObjectivesThe aim was to assess the performance of low-dose non-contrast CT of the urinary tract (LD-CT) acquired at radiation exposures close to that of abdominal radiography using adaptive statistical iterative reconstruction (ASiR).MethodsThirty-three patients with clinically suspected renal colic were prospectively included. Conventional dose (CD-CT) and LD-CT data sets were contemporaneously acquired. LD-CT images were reconstructed with 40 %, 70 % and 90 % ASiR. Image quality was subjectively and objectively measured. Images were also clinically interpreted.ResultsMean ED was 0.48 ± 0.07 mSv for LD-CT compared with 4.43 ± 3.14 mSv for CD-CT. Increasing the percentage ASiR resulted in a step-wise reduction in mean objective noise (p < 0.001 for all comparisons). Seventy % ASiR LD-CT images had higher diagnostic acceptability and spatial resolution than 90 % ASiR LD-CT images (p < 0.001). Twenty-seven calculi (diameter = 5.5 ± 1.7 mm), including all ureteric stones, were correctly identified using 70 % ASiR LD-CT with two false positives and 16 false negatives (diameter = 2.3 ± 0.7 mm) equating to a sensitivity and specificity of 72 % and 94 %. Seventy % ASiR LD-CT had a sensitivity and specificity of 87 % and 100 % for detection of calculi >3 mm.ConclusionReconstruction of LD-CT images with 70 % ASiR resulted in superior image quality than FBP, 40 % ASIR and 90 % ASIR. LD-CT with ASIR demonstrates high sensitivity and specificity for detection of calculi >3 mm.Teaching Points• Low-dose CT studies for urinary calculus detection were performed with a mean dose of 0.48 ± 0.07 mSv• Low-dose CT with 70 % ASiR detected calculi >3 mm with a sensitivity and specificity of 87 % and 100 %• Reconstruction with 70 % ASiR was superior to filtered back projection, 40 % ASiR and 90 % ASiR images

Comparing Stone Attenuation in Low- and Conventional-Dose Noncontrast Computed Tomography

Noncontrast computed tomography (NCCT) has high sensitivity, specificity, and is able to predict stone composition using Hounsfield units (HU) but is associated with high radiation exposure. In an attempt to reduce radiation exposure, low-dose stone protocols have been developed that provide excellent detection of stones. It is not known, however, whether these protocols are equally effective in determining HU stone density. The purpose of this study is to compare stone HU attenuation between low- and conventional-dose NCCT. In this prospective randomized, single blinded study, 7-mm calcium oxalate stones were placed randomly into nine intact urinary systems and scanned in three different cadaveric vehicles. Holding other parameters constant, NCCT was performed at varying mAs levels ranging from 5 to 140. Identical magnified images at each mAs setting were reviewed in a blinded fashion to determine HU attenuation. Statistical analyses were performed using a Kruskal-Wallis test and the Levene test, with P<0.05 considered significant. In 19 different stone configurations with 133 stones, median attenuation levels were 614, 674, 681, 669, 670, 674, and 667 HU at 5, 7.5, 15, 30, 50, 70, and 140 mAs, respectively. The differences in median attenuation levels were not significantly different (P=0.998). An increasing trend of attenuation variability was noticed as the radiation dose decreased; however, this was not significant (P=1.0). Low-dose NCCT results in similar HU attenuation compared with conventional-dose NCCT. Although there is a slight increase in variability, low-dose NCCT provides similar information to assist in determining stone composition as conventional-dose NCCT.

Automated aorta segmentation in low-dose chest CT images

Abnormalities of aortic surface and aortic diameter can be related to cardiovascular disease and aortic aneurysm. Computer-based aortic segmentation and measurement may aid physicians in related disease diagnosis. This paper presents a fully automated algorithm for aorta segmentation in low-dose non-contrast CT images. The original non-contrast CT scan images as well as their pre-computed anatomy label maps are used to locate the aorta and identify its surface. First a seed point is located inside the aortic lumen. Then, a cylindrical model is progressively fitted to the 3D image space to track the aorta centerline. Finally, the aortic surface is located based on image intensity information. This algorithm has been trained and tested on 359 low-dose non-contrast CT images from VIA-ELCAP and LIDC public image databases. Twenty images were used for training to obtain the optimal set of parameters, while the remaining images were used for testing. The segmentation result has been evaluated both qualitatively and quantitatively. Sixty representative testing images were used to establish a partial ground truth by manual marking on several axial image slices. Compared to ground truth marking, the segmentation result had a mean Dice Similarity Coefficient of 0.933 (maximum 0.963 and minimum 0.907). The average boundary distance between manual segmentation and automatic segmentation was 1.39 mm with a maximum of 1.79 mm and a minimum of 0.83 mm. Both qualitative and quantitative evaluations have shown that the presented algorithm is able to accurately segment the aorta in low-dose non-contrast CT images.

Adequacy of Low Dose Computed Tomography in Patients Presenting with Acute Urinary Colic

Noncontrast abdominal/pelvic CT is the current imaging standard for patients who present with acute urinary colic. Conventional CT, however, exposes the patient to significant amounts of ionizing radiation, which is cumulative when additional CTs are used to monitor stone migration, outcomes, etc. We sought to maintain diagnostic adequacy while decreasing our patients' radiation exposure from CT by using a reduced tube current, an abbreviated scanning area, and the use of coronal reformatted images. Between March 3, 2011 and October 31, 2011, 101 consecutive adult patients with suspected urinary colic were evaluated with a "low" dose CT. If the suspected calculus(i) was not seen, the patient underwent immediate conventional CT imaging customized to their body habitus. Radiation exposure for each patient was calculated using an established formula of dose length product and scan length. The effective total radiation dose was measured in millisieverts (mSv). Overall, 84 patients had an upper tract calculus(i) consistent with the clinical suspicion. Of these, 76 (90%) were adequately imaged with low dose and 8 (10%) with conventional noncontrast CTs. The mean effective radiation dose in the 76 low dose stone-positive CTs was 2.14 mSV (median 2.10 mSv). This was almost seven-fold lower than the mean conventional stone-positive CT dose of 14.5 mSv (median 13.1 mSv). Low dose noncontrast CT provided adequate imaging to guide optimal urologic management in the majority of our patients. This modality offered a significantly lower ionizing radiation dose and should be considered in patients who present with acute urinary colic.

Limitations of Ultrasonography in the Evaluation of Urolithiasis: A Correlation With Computed Tomography

Cumulative radiation exposure from imaging studies is hazardous. In chronic diseases such as urolithiasis, efforts are made to limit radiation exposure, particularly for routine surveillance. We sought to determine the correlation of ultrasonography (US) compared with noncontrast CT (NCCT) in detecting and determining size of stones. Findings were evaluated in patients who underwent both imaging modalities within a 90-day period between July 2008 and June 2010. Urinary calculi were noted on NCCT in 72 patients. The sensitivity of US to determine the number, size, and location of the stones as described on official radiology reports were compared in reference to NCCT. There were 203 urinary calculi in 90 urinary tracts identified on NCCT imaging. The sensitivity, specificity, and accuracy of detecting specific stones on US were 40%, 84%, and 53%. Correlation between US and NCCT findings decreased with smaller stone size and ureteral location and increased with right-sided laterality. For identified stones, larger stone size discrepancies were noted in up to one-third of stones on US. Despite concern for excessive radiation exposure, urologists should recognize limitations of US in the evaluation of urolithiasis. As the ideal study to image stones, particularly for routine surveillance, remains unclear, tese data also supports the need for low-dose NCCT protocols and/or selective use of alternative modalities, such as magnetic resonance urography.

Unusual Finding of Thoracic Kidney on Myocardial Perfusion Imaging Using SPECT/CT

Noncardiac abnormalities are not uncommon in myocardial perfusion imaging. With the advent of SPECT/CT hybrid system, CT could produce high-quality attenuation maps to improve resolution. In addition, extracardiac abnormalities are easily differentiated by using SPECT/CT. We report a 47year-old man who felt chest tightness on exertion for 2 months. He denied hypertension, diabetes mellitus, or hyperlipidemia. Dipyridamole stress and redistribution myocardial SPECT revealed no perfusion defect. However, a retrocardiac mass with focal radioactivity was identified in the projection images, corresponding to a kidney shadow in the low-dose noncontrast CT scan. Subsequent conventional CT scan confirmed the diagnosis of thoracic renal ectopia.

Value of contrast-enhanced multiphase CT in combined PET/CT protocols for oncological imaging

To evaluate the additional value of contrast-enhanced multiphase CT in comparison with low-dose non-contrast CT in combined positron emission tomography (PET)/CT protocols for oncological imaging, we retrospectively analysed 100 patients with different malignant tumours. All patients underwent a PET/CT consisting of a multiphase CT protocol including a low-dose non-enhanced attenuation scan and an arterial and portal-venous contrast-enhanced scan followed by a whole-body PET. PET/CT studies were analysed by different categories to determine the added value of contrast-enhanced CT. The additional value was defined as new information provided by diagnostic CT and not available from the low-dose CT, resulting in change of PET/CT interpretation. The results were validated either by histopathology or by clinical-radiological follow up at > or =6 months. The clinical impact was evaluated with respect to changes in patient management. Diagnostic multiphase CT was of additional value in 52 out of 100 patients with 85 suspected lesions. In 40 out of 100 patients, no additional value could be detected. Eight patients were excluded due to inconclusive diagnosis in both methods including fusion. The analysis showed the greatest benefit of diagnostic CT in the categories localization of pathological fluorodeoxyglucose (FDG) uptake and precise tumour delineation, changing PET/CT interpretation in 42% and 31% of patients, respectively. The benefit of diagnostic CT was influenced by the tumour type demonstrating the highest impact in gastrointestinal, lung and neuroendocrine tumours. Diagnostic CT changed clinical management in 21 patients (21%). Diagnostic multiphase CT as part of the combined PET/CT protocol has the potential to provide considerable additional value in specific clinical conditions with resultant change of management in a substantial proportion of patients.