Dual-Energy CT for the Musculoskeletal System

Accuracy, agreement, and reliability of DECT-derived vBMD measurements: an initial ex vivo study

OBJECTIVES

To assess the agreement and reliability of DECT (dual-energy CT)-derived vBMD (volumetric bone mineral density) measurements from excised human femoral heads and to compare DECT-derived BMD with that measured by DXA (dual-energy X-ray absorptiometry) and QCT (quantitative CT) to determine its accuracy.

METHODS

Twenty patients that underwent total hip arthroplasty were enrolled to this study. Femoral heads were excised to rectangles without cortical bones for scanning. A dual-source DECT scanner generated images under 80/Sn140 kVp and 100/Sn140 kVp scanning conditions. Specimens were subsequently scanned by QCT and DXA to produce QCT-derived vBMD (mg/cm³) and DXA-derived BMM (bone mineral mass, g). DECT images were loaded to a post-processing workstation to calculate DECT-derived vBMD and BMM.

RESULTS

Higher DECT-derived vBMD and BMM were found under 80/Sn140 and 100/Sn140 kVp compared with those for QCT and DXA (p = 0.005). DECT-derived vBMD was highly correlated with QCT-derived vBMD (r = 0.961 ~ 0.993, p < 0.05). Similarly, DECT-derived BMM was strongly correlated with DXA-derived BMM (r = 0.927 ~ 0.943, p < 0.05). Agreement of the inter- and intra-observation of DECT-derived vBMD was excellent. Linear regression was carried out to calibrate DECT-derived vBMD of 80/Sn140 kVp (14 + 0.7 × DECT-derived vBMD) and 100/Sn140 kVp (74 + 0.4 × DECT-derived vBMD) with the reference of QCT-derived vBMD. After calibration, excellent agreement was found for vBMD and BMM within various imaging modalities.

CONCLUSIONS

Our study showed that DECT-derived vBMD exhibited high agreement and reliability features, and after calibration, it also displayed a high degree of accuracy. However, in vivo studies are needed to extend its potential utility in clinical settings.

KEY POINTS

• Measurements of DECT-derived vBMD had high intra- and inter-observer agreement and reliability. • Measurements of DECT-derived vBMD and BMM had a high correlation with those derived from QCT and DXA. • DECT-derived vBMD and BMM were accurate after calibration compared with QCT and DXA.

Imaging and Laboratory Workup for Hand Infections

Hand infections can lead to significant morbidity if not treated promptly. Most of these infections, such as abscesses, tenosynovitis, cellulitis, and necrotizing fasciitis, can be diagnosed clinically. Laboratory values, such as white blood cell count, erythrocyte sedimentation rate, C-reactive protein, and recently, procalcitonin and interleukin-6, are helpful in supporting the diagnosis and trending disease progression. Radiographs should be obtained in all cases of infection. Ultrasound is a dynamic study that can provide quick evaluation of deeper structures but is operator dependent. Computed tomographic and MRI studies are useful for evaluating deep space or bony infections and preoperative surgical planning.

Differentiating Rheumatoid and Psoriatic Arthritis of the Hand: Multimodality Imaging Characteristics

Accurate diagnosis and therapeutic intervention at an early stage is paramount for the management of rheumatoid arthritis (RA) and psoriatic arthritis (PsA), which are the two major types of inflammatory arthritis that involve the hand joints. As more disease-specific medications are developed, medication selection according to the correct diagnosis becomes more important. A delay in diagnosis and inappropriate medication selection may result in poor functional prognosis. However, clinical differentiation between RA and PsA can be challenging and may become largely dependent on imaging interpretation results. Although there is substantial overlap in the imaging findings of RA and PsA, there are differences in the affected primary target sites, reflected by the various patterns of joint involvement, and different microanatomic localization of abnormalities within a single joint in each disease. Therefore, appropriate use of various imaging modalities and accurate image interpretation add significant value to the diagnosis and treatment process. The synovio-entheseal complex is an important concept for understanding the imaging features of PsA. The authors review the different features of RA and PsA of the hands seen with various imaging modalities, including radiography, US, MRI, and dual-energy CT, with updates on the contemporary role of imaging in diagnosis and treatment. The radiologist should have sufficient knowledge to interpret imaging findings and understand the strengths and weaknesses of each modality to recommend the appropriate imaging method and differentiate both diseases accurately. ^©RSNA, 2020.

Protocol Optimization and Implementation of Dual-Energy and Dual-Source Computed Tomography in Clinical Practice: Field of View, Speed, or Material Separation?

Clinical use of dual-energy computed tomography (DECT) and dual-source computed tomography (DSCT) has been well established for more than a decade. Improved software and decreased postprocessing time have increased the advantages and availability of DECT and DSCT imaging. In this article, we will provide a practical guide for implementation of DECT and DSCT in clinical practice and discuss automated processing and selection of CT protocols in neurologic, cardiothoracic, vascular, body, and musculoskeletal imaging.

Added value of color-coded virtual non-calcium dual-energy CT in the detection of acute knee fractures in non-radiology inexpert readers

PURPOSE

To evaluated the added value of dual-energy CT (DECT) virtual non-calcium (VNCa) protocol on conventional CT in the detection of acute knee fractures in non-radiology inexpert readers.

METHOD

One hundred fifty-six patients (mean age, 51.97 years; age range, 17-86 years) with knee trauma, who underwent DECT and MRI within 3 days between April 2017 and October 2018, were retrospectively analyzed. Three readers (intern, 1st-year general surgery resident, 1st-year emergency medicine resident) independently analyzed CT alone and then with the additional color-coded DECT VNCa for fractures. A board-certified radiologist, analyzed CT and MRI series to define the reference standard. Sensitivity, specificity, and AUC were compared between the two reading sessions.

RESULTS

Fifty-seven patients had acute fractures and 99 had no fractures. Thirteen of 57 fractures were nondisplaced. The additional use of VNCa images significantly increased the mean AUC (reader 1: 0.813 vs. 0.919; reader 2: 0.842 vs. 0.930; reader 3: 0.837 vs. 0.921; P < 0.05). When only nondisplaced fractures included, the mean AUC was more increased in the combined analysis of CT and DECT VNCa (reader 1: 0.521 vs. 0.916; reader 2: 0.542 vs. 0.926; reader 3: 0.575 vs. 0.926; P <  .01). Sensitivity increased by 15 %-20 % in total fracture group and by 69 %-77 % in nondisplaced fracture group over that with CT alone when both CT and DECT VNCa were used. Specificity did not differ significantly.

CONCLUSIONS

The additional use of color-coded DECT VNCa protocol to conventional CT improved diagnostic performance in detecting acute knee fractures for inexperienced non-radiology readers.

Towards Robust and Accurate Detection of Abnormalities in Musculoskeletal Radiographs with a Multi-Network Model

This study proposes a novel multi-network architecture consisting of a multi-scale convolution neural network (MSCNN) with fully connected graph convolution network (GCN), named MSCNN-GCN, for the detection of musculoskeletal abnormalities via musculoskeletal radiographs. To obtain both detailed and contextual information for a better description of the characteristics of the radiographs, the designed MSCNN contains three subnetwork sequences (three different scales). It maintains high resolution in each sub-network, while fusing features with different resolutions. A GCN structure was employed to demonstrate global structure information of the images. Furthermore, both the outputs of MSCNN and GCN were fused through the concat of the two feature vectors from them, thus making the novel framework more discriminative. The effectiveness of this model was verified by comparing the performance of radiologists and three popular CNN models (DenseNet169, CapsNet, and MSCNN) with three evaluation metrics (Accuracy, F1 score, and Kappa score) using the MURA dataset (a large dataset of bone X-rays). Experimental results showed that the proposed framework not only reached the highest accuracy, but also demonstrated top scores on both F1 metric and kappa metric. This indicates that the proposed model achieves high accuracy and strong robustness in musculoskeletal radiographs, which presents strong potential for a feasible scheme with intelligent medical cases.

The utility of dual energy computed tomography in the management of axial gout: case reports and literature review

Background

Severe spinal pain is an unusual presentation of gout. Due to its rarity and the difficulty of obtaining joint fluid or tissue for crystal analysis, dual energy computed tomography (DECT) may be a useful imaging modality in the management of axial gout.

Case presentation

Two patients independently presented to a major teaching hospital with severe spinal pain subsequently shown to be due to gout. The first patient presented with back pain and fevers and was initially thought to have lumbar facet joint septic arthritis. The second case presented with severe back pain. In both cases, DECT suggested monosodium urate deposition in spinal tissues as the cause of their presentation.

Conclusions

Axial gout should be considered in the differential diagnosis of severe spinal pain. A DECT study may be a useful diagnostic tool in the management of spinal gout.

The accurate relationship between spine bone density and bone marrow in humans

CONTEXT

The accuracy of QCT measurements of lumbar spine trabecular volumetric bone mineral density (vBMD) is decreased due to differences in the amount of bone marrow adipose tissue (BMAT).

OBJECTIVE

To correct vBMD measurements for differences in marrow composition and investigate the true relationship between vBMD and BMAT.

DESIGN

Cross-sectional study.

SETTING

University teaching hospital.

PARTICIPANTS

Healthy Chinese subjects (233 women, 167 men) aged between 21 and 82 years.

MAIN OUTCOME MEASURES

vBMD and BMAT were measured using QCT (120 kV) and chemical shift-encoded MRI of the L2-L4 vertebrae. vBMD measurements were standardized to the European Spine Phantom (ESP) and corrected for differences in BMAT. Linear regression was used to analyze BMAT, ESP adjusted vBMD (vBMD_ESPcorr) and BMAT corrected vBMD (vBMD_BMATcorr) against age and corrected vBMD against BMAT.

RESULTS

BMAT in the L2-L4 vertebral bodies increased with age in both sexes, with a faster rate of change in women compared with men (0.54%/year vs. 0.27%/year, P < 0.0001). After vBMD measurements were corrected for BMAT there were statistically significant changes in the slope of the regression line with age in both sexes (women: -3.00 ± 0.13 vs. -2.57 ± 0.11 mg/cm³/year, P < 0.0001; men: -1.92 ± 0.15 vs. -1.70 ± 0.14 mg/cm³/year, P < 0.0001). When vBMD_BMATcorr was plotted against BMAT, vBMD decreased linearly with increasing BMAT in both sexes (women: -3.30 ± 0.18 mg/cm³/%; men: -2.69 ± 0.25 mg/cm³/%, P = 0.048).

CONCLUSION

Our approach reveals the true relationship between vBMD and BMAT and provides a new tool for studying the interaction between bone and marrow adipose tissue.

Cartilage icing and chondrocalcinosis on knee radiographs in the differentiation between gout and calcium pyrophosphate deposition

Objective

To determine if findings of “cartilage icing" and chondrocalcinosis on knee radiography can differentiate between gout and calcium pyrophosphate deposition (CPPD).

Methods

IRB-approval was obtained and informed consent was waived for this retrospective study. Electronic medical records from over 2.3 million patients were searched for keywords to identify subjects with knee aspiration-proven cases of gout or CPPD. Radiographs were reviewed by two fellowship-trained musculoskeletal radiologists in randomized order, blinded to the patients’ diagnoses. Images were evaluated regarding the presence or absence of cartilage icing, chondrocalcinosis, tophi, gastrocnemius tendon calcification, and joint effusion. Descriptive statistics, sensitivity, specificity, positive and negative predictive values, and accuracy were calculated.

Results

From 49 knee radiographic studies in 46 subjects (31 males and 15 females; mean age 66±13 years), 39% (19/49) showed gout and 61% (30/49) CPPD on aspiration. On knee radiographs, cartilage icing showed a higher sensitivity for CPPD than gout (53–67% and 26%, respectively). Chondrocalcinosis also showed a higher sensitivity for CPPD than gout (50–57% versus 5%), with 95% specificity and 94% positive predictive value for diagnosis of CPPD versus gout. Soft tissue tophus-like opacities were present in gout at the patellar tendon (5%, 1/19) and at the popliteus groove in CPPD (15%, 4/27). Gastrocnemius tendon calcification was present in 30% (8/27) of subjects with CPPD, and 5% (1/19) of gout.

Conclusion

In subjects with joint aspiration-proven crystal disease of the knee, the radiographic finding of cartilage icing was seen in both gout and CPPD. Chondrocalcinosis (overall and hyaline cartilage) as well as gastrocnemius tendon calcification positively correlated with the diagnosis of CPPD over gout.

Metal artifact reduction by monoenergetic extrapolation of dual-energy CT in patients with metallic implants

PURPOSE

The objective of this study is to assess artifact reduction and image quality using dual-energy computed tomography (DECT) and metal artifact reduction techniques in patients with metallic implants.

METHODS

Forty patients with metallic implants, who had targeted CT performed by DECT during March to September 2018, were prospectively recruited. Post-processing with monoenergetic extrapolation at 70 and 150 keV was performed. Forty matched controls with metallic implants with single-energy CT (SECT) performed were selected. Attenuation value, noise, and signal-to-noise ratio (SNR) at the site of maximal artifact were measured at muscle and fat areas. Image quality of three sets of images (70 keV, 150 keV, and SECT) was assessed by two independent reviewers using a 5-point Likert-type scale. Statistical analysis of measured values, Likert-type scales, and radiation doses (volume CT dose index (CTDI_vol)) of DECT and SECT were performed with Mann-Whitney U test.

RESULTS

As compared to SECT, high keV reconstruction of DECT show (1) significantly higher values within muscle and fat surrounding the implant (DECT vs. SECT-muscle: -96 Hounsfield units (HU) vs. -405 HU, fat: -115 HU vs. -301 HU; p < 0.001), (2) significantly lower mean image noise (75 HU vs. 129 HU; p = 0.02), and (3) higher SNR (-0.8 vs. -4.3; p < 0.001). In addition, image quality of high keV reconstruction was rated superior to the other two groups on Likert-type scales ( p < 0.001). The mean radiation doses (CTDI_vol) were comparable between DECT and SECT (14.2 mGy vs. 19.3 mGy; p = 0.08).

CONCLUSION

For patients with metallic implants, monoenergetic extrapolation of DECT at high keV can reduce metal artifacts, increase SNR, and improve qualitative image quality at comparable radiation dose.

Metal artifact reduction of orthopedics metal artifact reduction algorithm in total hip and knee arthroplasty

The purpose of this study was to investigate metal artifact reduction effect of orthopedics metal artifact reduction (O-Mar) algorithm in computer tomography (CT) image of patients who have undergone total hip arthroplasty (THA) or total knee arthroplasty (TKA).35 cases of patients who underwent TKA or THA have been recruited in this study. CT image of hip or knee joint was obtained with Philips 256-row CT scanner. Tube voltages of 120 and 140 kilovolt peak (KVP) were set. Afterwards, CT image was reconstructed by O-Mar algorithm to reduce metal artifact. Grade of image quality and severity of metal artifact would be taken into qualitative evaluation. While, quantitative evaluation mainly included measurement of metal artifact volume and 2D measurement of average CT value in region of interest (ROI). The visibility of interface between bone-prostheses was also estimated.Result of qualitative analysis indicated that score of CT quality was improved and grade of metal artifact was decreased significantly with O-Mar. Quantitative analysis illustrated that volume of beam-hardening (B-H) metal artifact decreased remarkably after reconstruction of O-Mar (P < .001). In addition, O-Mar algorithm reduced 83.3% to 83.7% volume of photon-starvation (P-S) metal artifact. As for result of 2D measurement, CT value in ROI was closer to standard value in O-Mar group CT image (P < .001). Meanwhile, error of CT value also decreased significantly after reconstruction of O-Mar algorithm. Visibility rate of bone-prosthesis interface improved from 34.3% (Non-O-Mar) to 66.7% (O-Mar).O-Mar algorithm could significantly reduce metal artifact in CT image of THA and TKA in both 2D and three-dimensional (3D) level. Therefore, better image quality and visibility of bone-prostheses interface could be presented. In this study, O-Mar was proved as an efficient metal artifact reduction method in CT image of THA and TKA.

Fast kilovoltage (KV)-switching dual-energy computed tomography hydroxyapatite (HAP)-water decomposition technique for identifying bone marrow edema in vertebral compression fractures

Background

Hydroxyapatite (HAP) is the main component of bone mineral. The utility of using HAP-water decomposition technique with fast kilovoltage (KV)-switching dual-energy computed tomography (DECT) to detect abnormal edema in vertebral compression fractures (VCFs) has not been widely reported.

Methods

A total of 31 consecutive patients with 80 VCFs who underwent DECT and magnetic resonance imaging (MRI) of the spine were retrospectively enrolled in our study between October 2018 and January 2019. VCFs in MR examinations served as the standard of reference. Two radiologists blindly and independently evaluated color-coded overlay virtual nonhydroxyapatite (VNHAP) images for the presence of abnormal edema. The inter-reader agreement, specificity, sensitivity, accuracy, and predictive values of VNHAP images for edema detection were calculated. The diagnostic accuracy of two readers was compared using McNemar's test. Two additional radiologists performed a quantitative analysis on VNHAP images, receiver operating characteristic (ROC) curve analysis was conducted, and the threshold was calculated.

Results

MRI depicted 45 edematous and 35 nonedematous VCFs. For visual analysis, the VNHAP technique showed a sensitivity of 93.3%, a specificity of 97.1%, a positive predictive value (PPV) of 97.7%, a negative predictive value (NPV) of 91.9%, and an accuracy of 95.0%. The inter-reader agreement was almost perfect (k=0.90). The diagnostic accuracy of the two readers showed no significant differences in the assessment of VNHAP images (P=1.00). Significant differences in CT numbers between vertebrae with and without bone marrow edema were found by quantitative analysis (P<0.01). The area under the curve (AUC) of the VNHAP images was estimated to be 0.917. The threshold of 1,003.2 mg/cm³ yielded a sensitivity of 88.9% and a specificity of 82.9% for the differentiation of fresh and old VCFs.

Conclusions

Fast KV-switching DECT HAP-water decomposition technique had excellent diagnostic performance for identifying acute and chronic VCFs in visual and quantitative analyses.

Dual-energy CT characterization of winter sports injuries

CT is a readily available imaging modality for cross-sectional characterization of acute musculoskeletal injuries in trauma. Dual-energy CT provides several additional benefits over conventional CT, namely assessment for bone marrow edema, metal artifact reduction, and enhanced assessment of ligamentous injuries. Winter sports such as skiing, snowboarding, and skating can result in high speed and high energy injury mechanisms; dual-energy CT is well suited for the characterization of those injuries.

X-ray-based quantitative osteoporosis imaging at the spine

Osteoporosis is a metabolic bone disease with a high prevalence that affects the population worldwide, particularly the elderly. It is often due to fractures associated with bone fragility that the diagnosis of osteoporosis becomes clinically evident. However, early diagnosis would be necessary to initiate therapy and to prevent occurrence of further fractures, thus reducing morbidity and mortality. X-ray-based imaging plays a key role for fracture risk assessment and monitoring of osteoporosis. Whereas over decades dual-energy X-ray absorptiometry (DXA) has been the main method used and still reflects the reference standard, another modality reemerges with quantitative computed tomography (QCT) because of its three-dimensional advantages and the opportunistic exploitation of routine CT scans. Against this background, this article intends to review and evaluate recent advances in the field of X-ray-based quantitative imaging of osteoporosis at the spine. First, standard DXA with the recent addition of trabecular bone score (TBS) is presented. Secondly, standard QCT, dual-energy BMD quantification, and opportunistic BMD screening in non-dedicated CT exams are discussed. Lastly, finite element analysis and microstructural parameter analysis are reviewed.

Dual energy CT: a step ahead in brain and spine imaging

OBJECTIVE

The purpose of this pictorial essay is to illustrate the utility of dual energy CT as an adjunct or alternative to routine single energy CT (SECT) scan of the brain and spine in emergency neuroradiology practice.

CONCLUSION

Dual energy CT can be used as a problem-solving tool in brain and spine imaging. It enables one to make a confident and accurate diagnosis for a variety of clinical conditions thereby impacting patient management.

Dual energy CT can aid in the emergent differentiation of acute traumatic and pathologic fractures of the pelvis and long bones

PURPOSE

To determine whether dual energy CT (DECT) scanning can aid in the differentiation between acute traumatic and pathologic fractures of the pelvis and long bones.

METHODS

Retrospective review of 11 patients with 15 pathologic fractures proven by biopsy and/or other advanced imaging modalities. Age- and sex-matched patients with non-pathologic traumatic fractures were used as controls. Studies were reviewed by two readers on syngo.via software before and after the creation of virtual bone marrow color maps. Hounsfield units (HU) of the marrow space at the level of the fracture were recorded on both reviews. Differences between the HU of the bone marrow of traumatic and pathologic fractures were compared using two-tailed unpaired t-test.

RESULTS

A statistically significant difference was found in the HU of the affected bone marrow on DECT virtual noncalcium bone marrow color maps between the pathologic group (mean HU:4.89) and the non-pathologic group (mean HU: - 286.2) (p = 0.0177). HU measurements on the mixed kVp images were 150.4 for the pathologic and 94.1 for the non-pathologic fracture groups, respectively, with no statistical significance (p = 0.272).

CONCLUSIONS

DECT scanning can aid in the differentiation between hematoma at acute traumatic fracture sites and neoplasm at pathologic fracture sites. HU of the bone marrow is higher for pathologic fractures, and the difference in bone marrow attenuation is more evident on the virtual bone marrow color maps.

Extra-abdominal dual-energy CT applications: a comprehensive overview

Unlike conventional computed tomography, dual-energy computed tomography is a relatively novel technique that exploits ionizing radiations at different energy levels. The separate radiation sets can be achieved through different technologies, such as dual source, dual layers or rapid switching voltage. Body tissue molecules vary for their specific atomic numbers and electron density, and the interaction with different sets of radiations results in different attenuations, allowing to their final distinction. In particular, iodine recognition and quantification have led to important information about intravenous contrast medium delivery within the body. Over the years, useful post-processing algorithms have also been validated for improving tissue characterization. For instance, contrast resolution improvement and metal artifact reduction can be obtained through virtual monoenergetic images, dose reduction by virtual non-contrast reconstructions and iodine distribution highlighting through iodine overlay maps. Beyond the evaluation of the abdominal organs, dual-energy computed tomography has also been successfully employed in other anatomical districts. Although lung perfusion is one of the most investigated, this evaluation has been extended to narrowly fields of application, such as musculoskeletal, head and neck, vascular and cardiac. The potential pool of information provided by dual-energy technology is already wide and not completely explored, yet. Therefore, its performance continues to raise increasing interest from both radiologists and clinicians.

Bone marrow edema in non-traumatic hip: high accuracy of dual-energy CT with water-hydroxyapatite decomposition imaging

OBJECTIVES

To evaluate the diagnostic performance of dual-energy CT with water-hydroxyapatite (HAP) imaging for bone marrow edema in patients with non-traumatic hip pain.

METHODS

Forty patients (mean age, 58 years; 16 male and 24 female) who underwent rapid kVp-switching dual-energy CT and MRI within 1 month between April 2018 and February 2019 with hip pain but no trauma were enrolled. Two radiologists retrospectively evaluated 80 hip joints for the presence, extent (femoral head involved, head and neck, and head to intertrochanter), and severity (mild edema, moderate, severe) of bone marrow edema on dual-energy water-HAP images. Water mass density (mg/cm³) on water-HAP images was determined with region of interest-based quantitative analysis. MRI served as the standard of reference.

RESULTS

Sensitivity, specificity, and accuracy of readers 1 and 2 for the identification of bone marrow edema in water-HAP images were 85% and 85%, 93% and 73%, and 89% and 79%, respectively. The area under the receiver operating characteristic curve was 0.96 for reader 1 and 0.91 for reader 2 for differentiation of the presence of edema from no edema. The optimal water mass density to classify the presence of edema for reader 1 was 951 mg/cm³ with 93% sensitivity and 93% specificity and for reader 2 was 957 mg/cm³ with 80% sensitivity and 80% specificity. The more severe the edema, the higher was the mean water density value (p < 0.035).

CONCLUSION

Dual-energy water-HAP images showed good diagnostic performance for bone marrow edema in patients with non-traumatic hip pain.

KEY POINTS

• Dual-energy water-HAP imaging depicts bone marrow edema in patients with non-traumatic hip pain and may serve as an alternative to MRI in select patients. • A cutoff value of 951 mg/cm³mean water mass density results in 93% sensitivity and 93% specificity for the detection of bone marrow edema. • The more severe the bone marrow edema, the higher the mean water density value.

Clinical utility of dual-energy CT used as an add-on to 18F FDG PET/CT in the preoperative staging of resectable NSCLC with suspected single osteolytic metastases

OBJECTIVE

To determine the clinical value of ¹⁸F-FDG-PET/CT and dual-energy virtual noncalcium CT to detect and identify single osteolytic metastases (SOM) in participants with non-small cell lung cancer (NSCLC).

MATERIALS AND METHODS

Forty-two participants (mean age, 63.5 years ± 10.1; range, 41-81 years) with suspected SOM diagnosed by whole-body ¹⁸F-FDG-PET/CT underwent non-enhanced dual-energy CT. All images were visually and quantitatively evaluated by two nuclear medicine physicians (R1 and R2) and two radiologists (R3 and R4) independently. The results of visual and quantitative analysis of ¹⁸F-FDG-PET/CT and dual-energy CT were compared with pathological results.

RESULTS

In the visual analysis, the specificity and positive predictive value of dual-energy CT for reader 1 and reader 2 is larger than the corresponding figures of¹⁸F-FDG-PET/CT for reader 3 and reader 4 (94.1% each vs 82.4%/76.5%; 95.2%/95.0% vs 88.9%/86.2%). The sensitivity and negative predictive value of dual-energy CT is relatively lower than the number of ¹⁸F-FDG-PET/CT for readers (80.0%/76.0% vs 96.0%/100.0%; 76.2%/72.7% vs 93.3%/100.0%, respectively). ROI-based analysis of SUV_max on PET/CT images and CT numbers on VNCa images showed a significant difference between metastases and non-metastases (P < 0.001 each).

CONCLUSIONS

Pre-surgical evaluation by combination of whole-body ¹⁸F-FDG-PET/CT and dual-energy CT could improve the classification of SOM and may further guide the surgical decision-making in participants with NSCLC.

Applications of dual energy CT in clinical practice: A pictorial essay

In dual-energy CT (DECT), two different x-ray spectra are used to acquire two image datasets of the same region, to allow the analysis of energy-dependent changes in the attenuation of different materials. Each type of material demonstrates a relatively specific change in attenuation between images obtained with a high-energy spectrum and those obtained with a low-energy spectrum. Based on the relatively specific change in attenuation with two different energies, material composition information can be obtained to allow tissue characterization. The DECT ability of material differentiation allows bone removal in various CT angiography studies and bone marrow edema depiction, while with material optimization, metal artefacts can be significantly reduced to almost nil. DECT allows material separation to differentiate uric acid crystals from calcium to determine the composition of urinary calculi and to diagnose gout. Using the DECT ability of material decomposition, iodine maps can be generated, which are useful in the evaluation of any enhancing lesion in the body without the need to obtain a plain scan and allow perfusion maps to be created in cases of pulmonary thromboembolism.

Improving Bone Mineral Density Assessment Using Spectral Detector CT

INTRODUCTION

Bone mineral density (BMD) analysis by Dual-Energy x-ray Absorptiometry (DXA) can have some false negatives due to overlapping structures in the projections. Spectral Detector CT (SDCT) can overcome these limitations by providing volumetric information. We investigated its performance for BMD assessment and compared it to DXA and phantomless volumetric bone mineral density (PLvBMD), the latter known to systematically underestimate BMD. DXA is the current standard for BMD assessment, while PLvBMD is an established alternative for opportunistic BMD analysis using CT. Similarly to PLvBMD, spectral data could allow BMD screening opportunistically, without additional phantom calibration.

METHODOLOGY

Ten concentrations of dipotassium phosphate (K2HPO4) ranging from 0 to 600 mg/ml, in an acrylic phantom were scanned using SDCT in four different, clinically-relevant scan conditions. Images were processed to estimate the K2HPO4 concentrations. A model representing a human lumbar spine (European Spine Phantom) was scanned and used for calibration via linear regression analysis. After calibration, our method was retrospectively applied to abdominal SDCT scans of 20 patients for BMD assessment, who also had PLvBMD and DXA. Performance of PLvBMD, DXA and our SDCT method were compared by sensitivity, specificity, negative predictive value and positive predictive value for decreased BMD.

RESULTS

There was excellent correlation (R2 >0.99, p < 0.01) between true and measured K2HPO4 concentrations for all scan conditions. Overall mean measurement error ranged from -11.5 ± 4.7 mg/ml (-2.8 ± 6.0%) to -12.3 ± 6.3 mg/ml (-4.8 ± 3.0%) depending on scan conditions. Using DXA as a reference standard, sensitivity/specificity for detecting decreased BMD in the scanned patients were 100%/73% using SDCT, 100%/40% using PLvBMD provided T-scores, and 90-100%/40-53% using PLvBMD hydroxyapatite density classifications, respectively.

CONCLUSIONS

Our results show excellent sensitivity and high specificity of SDCT for detecting decreased BMD, demonstrating clinical feasibility. Further validation in prospective clinical trials will be required.

An update on advanced dual-energy CT for head and neck cancer imaging

Introduction: Dual-energy-computed tomography (DECT) is an advanced form of computed tomography (CT) that enables spectral tissue characterization beyond what is possible with conventional CT scans. DECT can improve non-invasive diagnostic evaluation of the neck, especially for the evaluation of head and neck cancer. Areas covered: This article is a review of current applications of DECT for the evaluation of head and neck cancer, focusing largely on squamous cell carcinoma (HNSCC). The article will begin with a brief overview of principles and different approaches for DECT scanning. This will be followed by a review of different DECT applications in diagnostic imaging and radiation oncology, practical and workflow considerations, and various emerging advanced applications for tumor analysis, including the use of DECT datasets for radiomics and machine learning applications. Expert opinion: Using a multi-parametric approach, different DECT reconstructions can be used to improve diagnostic evaluation and surveillance of head and neck cancer, including improving visibility of HNSCC, determination of tumor boundaries and extent, and invasion of critical organs such as the thyroid cartilage. In the future, the large amount of quantitative information on DECT scans may be leveraged for improving radiomic and machine learning models for tumor characterization.

Body Weight-Based Protocols During Whole Body FDG PET/CT Significantly Reduces Radiation Dose without Compromising Image Quality:Findings in a Large Cohort Study

RATIONALE AND OBJECTIVES

To investigate radiation dose reduction during whole body fluorodeoxyglucose (¹⁸F-FDG) positron emission tomographic (PET)/computed tomography (CT) by employing weight-based protocols.

MATERIALS AND METHODS

One thousand and twenty-eight patients were referred for ¹⁸F-FDG PET/CT study with one of two protocols: conventional protocol I; 120 kVp, 120 mAs, 0.5 second rotation time, pitch 0.8 mm/rot across all body weights; four-tier body weight protocol II all used 140 kVp, 0.75 seconds rotation time and pitch 0.8 mm/rot: Protocol A (≤60 kg): 35 mAs, Protocol B (61-80 kg): 50 mAs, Protocol C (81-100 kg): 65 mAs, and Protocol D: (>101 kg): 100 mAs. All protocols employed tube current modulation. Quantitative and qualitative image visual grading characteristics assessed image quality.

RESULTS

Patient demographics demonstrated no significant difference between each protocol except for patient weight in weight protocol IIB (p < 0.009). Mean effective dose in all protocols were significantly lower in Protocol B compared to A (p < 0.009). Contrast-to-noise ratio demonstrated no differences between each protocol (p < 0.21) except for weight protocol in protocol IIA (<60 kg, p = 0.035) with the visual grading characteristics demonstrating preference over protocol II compared to I.

CONCLUSION

Significant reduction in radiation dose can be achieved using patient-specific body weight-based protocols during whole-body ¹⁸F-FDG PET/CT without compromising image quality when employing weight-based protocols.

Dual energy computed tomography virtual monoenergetic imaging: technique and clinical applications

Dual energy CT (DECT) has evolved into a commonly applied imaging technique in clinical routine due to its unique post-processing opportunities for improved evaluation of all body areas. Reconstruction of virtual monoenergetic imaging (VMI) series has shown beneficial effects for both non-contrast and contrast-enhanced DECT due to the flexibility to calculate low-keV VMI reconstructions to increase contrast and iodine attenuation, or to compute high-keV VMI reconstructions to reduce beam-hardening artefacts. The goal of this review article is to explain the technical background of VMI and noise-optimized VMI+ algorithms and to give an overview of useful clinical applications of the VMI technique in DECT of various body regions.

Assessing Vascularity of Osseous Spinal Metastases with Dual-Energy CT-DSA: A Pilot Study Compared with Catheter Angiography

BACKGROUND AND PURPOSE

Spine debulking surgery in patients with hypervascular spinal metastasis is associated with massive intraoperative blood loss, but currently, the vascularity of tumor is determined by invasive conventional angiography or dynamic contrast MR imaging. We aimed to investigate the usefulness of noninvasive dual-energy CT-DSA, comparing it with conventional angiography in evaluating the vascularity of spinal metastasis.

MATERIALS AND METHODS

We conducted a retrospective study from January to December 2018. A total of 15 patients with spinal metastasis undergoing dual-energy CT, conventional DSA, and subsequent debulking surgery were included. CT-DSA images were produced after rigid-body registration and subtraction between CT phases. Qualitative and quantitative assessments of tumor vascularity were conducted. Correlations between CT-DSA and conventional DSA results were evaluated using the Spearman coefficient. The mean enhancement in the estimated tumor volume and surgical blood loss was compared between hypervascular and nonhypervascular groups using the Wilcoxon rank sum test.

RESULTS

The CT-DSA and DSA results were strongly correlated, with ρ = 0.87 (P < .001). The DSA and the quantitative enhancement index also showed a strong correlation with ρ = 0.83 (P < .001). Wilcoxon rank sum testing between hypervascular and nonhypervascular CT-DSA groups showed a difference in enhancement indices (P = .0003). The blood loss between the hypervascular and nonhypervascular groups was nonsignificant (P = .09).

CONCLUSIONS

Dual-energy CT-DSA correlates well with conventional DSA in assessing the vascularity of spinal metastasis. It may serve as a noninvasive preoperative evaluation option before debulking surgery.

Initial experience with dual-energy computed tomography-guided bone biopsies of bone lesions that are occult on monoenergetic CT

OBJECTIVE

Our purpose was to determine whether dual-energy CT (DECT), specifically the bone marrow setting of the virtual noncalcium (VNCa) algorithm, could be used to identify and accurately biopsy suspected bone malignancies that were visible on magnetic resonance imaging (MRI), nuclear bone scintigraphy, or positron-emission tomography/computed tomography (PET/CT), but occult on monoenergetic computed tomography (CT) by virtue of being either isodense or nearly isodense to surrounding normal bone.

MATERIALS AND METHODS

We present 4 cases in which DECT was used to detect various malignant bone lesions and was successfully used to direct percutaneous DECT-guided bone biopsies.

RESULTS

Two of the lesions were solid tumor metastases (breast and prostate carcinoma), whereas two others were hematological malignancies (leukemia and lymphoma). This technique enabled us to confidently and accurately direct the biopsy needle into the target lesion.

CONCLUSION

The authors demonstrate that the DECT VNCa bone marrow algorithm may be helpful in identifying isodense bone lesions of various histologies and may be used to guide percutaneous bone biopsies. This technique may help to maximize diagnostic yield, minimize the number of passes into the region of concern, and prevent patients from undergoing repeat biopsy.

Correction of QCT vBMD using MRI measurements of marrow adipose tissue

OBJECTIVE

Quantitative computed tomography (QCT) measurements of volumetric bone mineral density (vBMD) are subject to errors due to variations in the amount of bone marrow adipose tissue (BMAT). The purpose of our study was to describe and validate a novel method to correct lumbar spine trabecular vBMD measurements for BMAT using chemical shift-encoded magnetic resonance imaging (CSE-MRI).

METHODS

CSE-MRI measurements of proton density fat fraction (PDFF) were used to correct QCT spine vBMD measurements for BMAT based on the H₂O and K₂HPO₄ basis set equivalent densities of bone, red and yellow bone marrow. BMAT corrected and uncorrected vBMD measurements of the L1 vertebra were compared with dual-energy QCT (DEQCT) measurements in 18 subjects (mean age: 68 y, range 60 to 93 y). A further 400 subjects (mean age: 53 y, range 21 to 82 y) had 120 kV_p single-energy QCT and CES-MRI scans of L2-L4 and the data used to simplify the adipose tissue correction by deriving a linear equation between the CSE-MRI vBMD correction and fractional BMAT content.

RESULTS

Application of the CSE-MRI derived vBMD correction changed the bias (95% limits of agreement) compared with DEQCT from 26.7 (11.0 to 42.4) mg/cm³ to 2.2 (-9.5 to 13.9) mg/cm³ at 80 kV_p, and from 22.4 (3.3 to 41.6) mg/cm³ to 2.9 (-12.6 to 18.4) mg/cm³ at 120 kV_p. Data for the 400 subjects gave the following relationship valid at 120 kV_p: vBMD correction (mg/cm³) = -12.96 + 75.76 × BMAT.

CONCLUSION

CSE-MRI measurements of PDFF can be used to correct for BMAT content and improve the accuracy of lumbar spine QCT vBMD measurements calibrated using a K₂HPO₄ phantom.

Radiologic evaluation of fracture healing

While assessment of fracture healing is a common task for both orthopedic surgeons and radiologists, it remains challenging due to a lack of consensus on imaging and clinical criteria as well as the lack of a true gold standard. Further complicating this evaluation are the wide variations between patients, specific fracture sites, and fracture patterns. Research into the mechanical properties of bone and the process of bone healing has helped to guide the evaluation of fracture union. Development of standardized scoring systems and identification of specific radiologic signs have further clarified the radiologist's role in this process. This article reviews these scoring systems and signs with regard to the biomechanical basis of fracture healing. We present the utility and limitations of current techniques used to assess fracture union as well as newer methods and potential future directions for this field.

Disk injury in patients with vertebral fractures-a prospective diagnostic accuracy study using dual-energy computed tomography

OBJECTIVES

Using magnetic resonance imaging (MRI) as the standard of reference, we aimed to evaluate the diagnostic accuracy of dual-energy computed tomography (DECT) in assessing disk injuries in patients aged more than 50 years with vertebral fractures.

METHODS

This prospective study was approved by the local ethics committee (EA1/372/14), and all patients gave written informed consent. Patients with suspected fractures underwent spinal DECTs and MRIs. Three readers scored DECT collagen maps for the presence or absence of disk injuries and also scored MR images according to the Sander classification (0-3). Only disks at risk (target disks) were included in the analysis. Sensitivity and specificity were calculated. Fleiss's κ was used to evaluate interrater agreement. Attenuation, in Hounsfield units, was compared between affected and unaffected disks in DECT.

RESULTS

Analyzing 295 disks in 67 patients, DECT was both sensitive (0.85) and specific (0.75). Sensitivity varied with the severity of disk damage, as assessed using the Sander scale (grade 1, 0.80; 2, 0.85; and 3, 0.98). Fleiss's κ was 0.41 for MRI and 0.51 for DECT. In the DECT collagen maps, attenuation was lower in injured disks compared to that in normal disks (80.3 ± 35.2 vs. 97.9 ± 41.0, p < 0.001).

CONCLUSIONS

Compared to conventional CT, DECT collagen maps can yield more diagnostic information, allowing identification of disk injuries in elderly patients with vertebral fractures.

KEY POINTS

• Dual-energy computed tomography allows vertebral disk injuries to be detected in elderly patients with vertebral fractures. • Dual-energy computed tomography yields more diagnostic information about vertebral disks compared to conventional CT. • Dual-energy computed tomography can be used as an alternative imaging modality for patients unwilling or unable to undergo MRI.

Light Bulb Procedure for the Treatment of Tarsal Navicular Osteonecrosis After Failed Percutaneous Decompression: A Case Report

Tarsal navicular osteonecrosis in adults is a rare condition with unclear etiology, and the optimal treatment has not been established. Here we report a case of tarsal navicular osteonecrosis with a complete course of treatment and comprehensive imaging studies starting at an early stage. A 37-year-old female diagnosed with tarsal navicular osteonecrosis was first treated with percutaneous decompression, but her symptoms persisted postoperatively. The tarsal navicular showed no further collapse, but follow-up magnetic resonance imaging (MRI) at 6 months postoperatively revealed persistent osteonecrotic changes. Debridement of the necrotic bone with preservation of the cortical shell and bone substitute packing for the defect (light bulb procedure) were performed. The symptoms resolved by 3 months postoperatively, and the patient could return to work. At a 6-year follow-up visit, the patient was free of symptoms, and MRI showed remodeling of the tarsal navicular without further collapse.

Virtual Noncalcium Dual-Energy CT: Detection of Lumbar Disk Herniation in Comparison with Standard Gray-scale CT

Purpose To assess the diagnostic performance of dual-energy CT with reconstruction of virtual noncalcium (VNCa) images for the detection of lumbar disk herniation compared with standard CT image reconstruction. Materials and Methods For this retrospective study, 41 patients (243 intervertebral disks; overall mean age, 68 years; 24 women [mean age, 68 years] and 17 men [mean age, 68 years]) underwent clinically indicated third-generation, dual-source, dual-energy CT and 3.0-T MRI within 2 weeks between March 2017 and January 2018. Six radiologists, blinded to clinical and MRI information, independently evaluated conventional gray-scale dual-energy CT series for the presence and degree of lumbar disk herniation and spinal nerve root impingement. After 8 weeks, readers reevaluated examinations by using color-coded VNCa reconstructions. MRI evaluated by two separate experienced readers, blinded to clinical and dual-energy CT information, served as the standard of reference. Sensitivity and specificity were the primary metrics of diagnostic performance. Results A total of 112 herniated lumbar disks were depicted at MRI. VNCa showed higher overall sensitivity (612 of 672 [91%] vs 534 of 672 [80%]) and specificity (723 of 786 [92%] vs 665 of 786 [85%]) for detecting lumbar disk herniation compared with standard CT (all comparisons, P < .001). Interreader agreement was excellent for VNCa and substantial for standard CT (κ = 0.82 vs 0.67; P < .001). VNCa achieved superior diagnostic confidence, image quality, and noise scores compared with standard CT (all comparisons, P < .001). Conclusion Color-coded dual-energy CT virtual noncalcium reconstructions show substantially higher diagnostic performance and confidence for depicting lumbar disk herniation compared with standard CT. © RSNA, 2018.

Diagnostic performance of dual-energy CT for the detection of bone marrow oedema: a systematic review and meta-analysis

OBJECTIVES

The aim of this systematic review and meta-analysis was to assess the sensitivity and specificity of dual-energy CT (DECT) for the detection of bone marrow oedema (BME).

METHODS

An electronic search of the PubMed and EMBASE databases was conducted. Bivariate modelling and hierarchical summary receiver-operating characteristic modelling were performed to evaluate the overall diagnostic performance of DECT for BME. Subgroup analysis was performed according to the assessment type (qualitative vs. quantitative) and anatomical location (spine vs. appendicular skeleton). Meta-regression analyses were performed according to the subject, study, and DECT characteristics.

RESULTS

Twelve eligible studies (1901 lesions, 450 patients) were included. DECT exhibited a pooled sensitivity of 0.85 [95% confidence interval (CI): 0.78-0.90] and a pooled specificity of 0.97 (95% CI: 0.92-0.98) for BME detection. In addition, the diagnostic performance of qualitative assessment (sensitivity, 0.85; specificity, 0.97) was higher than that of quantitative assessment (sensitivity, 0.84; specificity, 0.88) of DECT findings. The diagnostic performance of DECT for the spine (sensitivity, 0.84; specificity, 0.98) and appendicular skeleton (sensitivity, 0.84; specificity, 0.93) were excellent. According to meta-regression analysis, the use of a tin filter, ≥ 2 image planes, and a slice thickness < 1 mm tended to exhibit higher sensitivity and hyperacute stage BME (< 24 h) tended to exhibit lower sensitivity.

CONCLUSIONS

These findings indicate that DECT has excellent sensitivity and specificity for BME detection. Qualitative assessment of DECT findings obtained using a tin filter, ≥ 2 image planes, and a 0.5-1-mm slice thickness in the acute stage BME (≥24 h) is recommended for more sensitive diagnosis.

KEY POINTS

• Overall, DECT is useful for the detection of BME (sensitivity, 85%; specificity-97%). • Qualitative assessment (sensitivity-85%; specificity-97%) is more accurate than quantitative assessment (sensitivity-84%; specificity-88%). • DECT showed excellent diagnostic performance for both the spine/appendicular skeleton (sensitivity-84%/84%; specificity-98%/93%).

Referral Patterns for Dual-Energy Computed Tomography in Diagnosis and Management of Gout: Ten-Year Experience at a Canadian Institution

PURPOSE

To analyze the utilization, indications, and outcomes of dual-energy computed tomography (DECT) gout imaging in clinical practice.

METHODS

This retrospective study was ethics approved. Radiology reports of DECT gout scans between 2007 and 2016 were analyzed for trends of utilization, referral pattern, indication, and diagnosis.

RESULTS

DECT gout referrals increased substantially (2007: 37; 2008: 72; 2016: 385; total: 1877). The largest number of referrals were from rheumatology (1160), emergency medicine (283), and family medicine (177). Most referrals (92%) were requested to aid an initial diagnosis of gout. Other reasons included estimating the disease burden (6%) or monitoring disease progression and effectiveness of treatment (2%). Rheumatology accounted for most referrals for the latter two reasons (81% and 97%). Imaging findings of urate presence were similar in referrals from rheumatology (62%), family medicine (62%), and other medical specialties (62%). The urate positive rates were slightly lower in referrals from emergency medicine (47%) and surgical specialties (41%). The most common differential diagnoses by referring specialties were calcium pyrophosphate dihydrate crystal deposition disease (CPPD) and other inflammatory or erosive arthritides (rheumatology, family medicine), CPPD and infections (other medical specialties), infections and fractures (emergency medicine), neoplasm and infections (surgical specialties).

CONCLUSIONS

The increasing utilization of DECT for gout imaging validates its clinical value. Varying clinical presentation could explain differences of urate positive rates among specialties. Our results support a multispecialty collaborative approach to the diagnosis and management of gout, with direct access to DECT gout imaging provided to various physician specialties.

Metal Artifact Reduction in Virtual Monoenergetic Spectral Dual-Energy CT of Patients With Metallic Orthopedic Implants in the Distal Radius

OBJECTIVE

The purpose of this study was to evaluate the image quality of virtual monoenergetic images obtained from dual-layer-detector spectral CT of patients with metallic orthopedic implants of the distal radius.

MATERIALS AND METHODS

A retrospective analysis was performed between April 2016 and January 2017. Forty-three consecutively registered patients (33 women, 10 men; mean age, 50.7 ± 15.4 years) with metallic implants for distal radius fractures underwent dual-layer-detector spectral CT. Sixteen virtual monoenergetic image sets ranging from 50 to 200 keV were generated from the single slice with the most pronounced low-attenuation artifact from implants. Image quality was quantitatively assessed on the basis of the attenuation of the artifacts and reference tissue, background image noise, and artifact index. Qualitative assessment included degree of artifact, diagnostic image quality of the periimplant bones, and delineation of fracture lines. The Friedman rank sum test and kappa analysis were used for statistical analysis.

RESULTS

There were statistically significant differences in quantitative and qualitative parameters at different monoenergy levels (all p < 0.001). Artifact index was the lowest at 120 keV. Low-attenuation artifacts in the periimplant regions were least pronounced at 110 keV, and the diagnostic image quality of periimplant bone was best at 130 keV. Fracture lines were well delineated in all cases at 80-110 keV (p < 0.001).

CONCLUSION

The optimal energy setting for incurring the fewest metallic artifacts and obtaining the best diagnostic image quality from distal radius implants during dual-layer-detector spectral CT is the range of 110-130 keV.

Dual-energy contrast-enhanced CT to evaluate scaphoid osteonecrosis with surgical correlation

To evaluate the validity of contrast enhanced dual energy CT using a lung perfusion algorithm in assessing for post-traumatic scaphoid proximal pole avascular necrosis. From Aug 2013 to Aug 2016, 18 patients (19 wrists, 16 males, 2 females, mean age 28 years) were assessed as high-risk for proximal pole scaphoid avascular necrosis by a single surgeon following a scaphoid fracture and were referred for contrast-enhanced dual energy CT. 8 wrists had specimens sent for correlative histological analysis and 11 were correlated with operative notes. Eight surgical specimens were sent to histology and showed a 100% correlation (8/8) with the DECT findings. The remaining 11 wrists that did not have a specimen sent had in-surgery findings that also correlated with DECT. A single case was discrepant (1/11) due to presence of an intra-osseous ganglion, which was reported as osteonecrosis on CT, but considered viable at surgery. No case was called viable on CT that proved to be necrotic at either surgery or histologically. Contrast-enhanced dual energy CT using a perfusion algorithm is an innovative and promising method in evaluating viability of the post-trauma proximal pole of scaphoid.