Dual-energy CT angiography of pelvic and lower extremity arteries: dual-energy bone subtraction versus manual bone subtraction

Updates in Vascular Computed Tomography

Computed tomography angiography (CTA) has become a mainstay for the imaging of vascular diseases, because of high accuracy, availability, and rapid turnaround time. High-quality CTA images can now be routinely obtained with high isotropic spatial resolution and temporal resolution. Advances in CTA have focused on improving the image quality, increasing the acquisition speed, eliminating artifacts, and reducing the doses of radiation and iodinated contrast media. Dual-energy computed tomography provides material composition capabilities that can be used for characterizing lesions, optimizing contrast, decreasing artifact, and reducing radiation dose. Deep learning techniques can be used for classification, segmentation, quantification, and image enhancement.

Multi-Energy Computed Tomography Breast Imaging with Monte Carlo Simulations: Contrast-to-Noise-Based Image Weighting

CONTEXT

Photon-counting detectors and breast computed tomography imaging have been an active area of research. With these detectors, photons are assigned an equal weight and weighting schemes can be enabled. More weight can be assigned to lower energies, resulting in an increase in the contrast-to-noise ratio (CNR).

AIMS

The aim of this study is to develop and evaluate an energy weighting imaging technique to improve the CNR of simulated breast phantoms and to improve tumour detection.

MATERIALS AND METHODS

Breast phantoms consisting of adipose, glandular, malignant tissues and iodine contrast were constructed with BreastSimulator software. The phantoms were used in egs_cbct simulations for energies ranging between 20 and 65 keV from which multiple images were reconstructed. A new CNR-based image weighting method was proposed based on the CNR values obtained from the images. This method improves on previous methods and can be applied to complicated phantoms since no structural information is needed.

RESULTS

An increase in the CNR can be seen for lower energies. A sharp increase in the CNR is seen just above the K-edge for the phantoms with the iodine contrast. The CNR-based image weighting leads to a 68.47% (1.68-fold) increase in the CNR for the malignant tissue without iodine. For the malignant tissue with iodine contrast, the increase in the CNR was 96.14% (1.96-fold).

CONCLUSIONS

The new proposed CNR-based image weighting scheme is easy to implement and can be used for complicated phantoms with varying structures. A large increase in the CNR is seen with or without the use of iodine contrast.

CT Angiography in the Lower Extremity Peripheral Artery Disease Feasibility of an Ultra-Low Volume Contrast Media Protocol

Purpose

The ALARA principle is not only relevant for effective dose (ED) reduction, but also applicable for contrast media (CM) management. Therefore, the aim was to evaluate the feasibility of an ultra-low CM protocol in the assessment of peripheral artery disease (PAD).

Materials and methods

Fifty PAD patients were scanned on third-generation dual-source computed tomography, from diaphragm to the forefoot, as follows: tube voltage: 70 kV, reference effective tube current: 90 mAs, collimation: 192 × 2 × 0.6 mm, with individualized acquisition timing. The protocol ED (mSv) was quantified with dedicated software. CM protocol consisted of 15 ml test bolus and 30 ml main bolus (300 mgI/ml) injected at 5 ml/s, followed by a 40 ml saline chaser at the same flow rate. Aorto-popliteal bolus transit time was used to calculate the overall acquisition time and delay. Objective (hounsfield units—HU; contrast-to-noise ratio—CNR) and subjective image quality (four-point Likert score) were assessed at different anatomical regions from the aorta down to the forefoot.

Results

Mean attenuation values were exceeding 250 HU from aorta down to the anterior tibial artery with CNR < 13. However, decline in attenuation was observed in more distal region with mean values of 165 and 199 HU, in left and right dorsalis pedis artery, respectively. Mode subjective image quality from the level of aorta down to the popliteal segment was excellent; below the knee mode score was good. The mean ED per protocol was 1.1 ± 0.5 mSv.

Conclusion

Use of an ultra-low CM volume protocol at 70 kV is feasible in the evaluation of PAD, resulting in good to excellent image quality with mean ED of 1.1 ± 0.5 mSv.

Level of evidence

Level 3, Local non-random sample

Dual energy CT angiography in peripheral arterial stents: optimal scanning protocols with regard to image quality and radiation dose

Background

To determine the optimal scanning protocols of dual energy computed tomography angiography (DECTA) in terms of radiation dose and image quality assessment at different keV levels, and compare it with conventional computed tomography angiography (CTA) in patients treated with peripheral arterial stents.

Methods

Twenty-nine patients with previous stent placement in peripheral arteries were evaluated with DECTA. Images were reconstructed with virtual monochromatic spectral imaging (VMS) at 65, 68, 70 and 72 keV and adaptive statistical iterative reconstruction (ASIR) at 50% compared with CTA. Image quality comprising image noise, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were assessed, and radiation dose was compared. Effects of different type of peripheral arterial stents on image quality were also evaluated. Fifty-six uniquely identified stents that were located in common iliac arteries (CIA), external iliac arteries (EIA) and superficial femoral arteries (SFA) were evaluated.

Results

Within subjects, the results showed that DECTA images (VMS) had less noise than the CTA images for CIA, EIA and SFA stents, with the lowest noise at 72 keV. Also, the VMS images had greater SNR than the CTA images for the EIA stents (P<0.05); and the VMS images had greater CNR than the CTA images for CIA, EIA, and SFA stents (P<0.001). Also, on CT attenuation, VMS continued to outperform CTA, but to a lesser extent. Between subjects, average VMS noise varied significantly with the type of the stent used (P=0.025) for CIA stents. Radiation dose was highly significant between DECTA and conventional CTA scans (6.98 vs. 7.40 mSv, P=0.047).

Conclusions

We conclude that an optimal scanning protocol consisting of 72 keV and 50% ASIR leads to better image quality for DECTA in peripheral arterial stenting when compared to conventional CTA.

Dual-energy computed tomography angiography: virtual calcified plaque subtraction in a vascular phantom

BACKGROUND

Material decomposition of dual-energy computed tomography (DECT) enables subtraction of calcified plaque.

PURPOSE

To evaluate the accuracy of lumen area measurement in calcified plaque by subtraction of DECT and to determine the effect of contrast material concentration, lumen diameter, density, and thickness of calcified plaque for the measurement.

MATERIAL AND METHODS

Vessel phantoms were made with six lumen diameters (5.7, 4.9, 3.9, 3.0, 1.9, and 1.3 mm) and six types of calcified plaques with three densities and two thicknesses were attached. CT scans were performed with three contrast material concentrations (62, 111, and 170 mg iodine/mL). Lumen area discrepancy (AD) was calculated by subtracting the measured lumen area from a reference value. The lumen area underestimation percentage (AU), defined as (AD/reference value) × 100, was calculated. General linear model analysis was used to test the effect of variables for log-transformed AU (ln_AU).

RESULTS

The AD and AU was calculated to be 6.1 ± 4.8 mm² and 69.8 ± 29.4%, respectively. Ln_AU was significantly affected by contrast material concentration (P < 0.001), calcium density (P = 0.001), plaque thickness (P = 0.010), and lumen diameter (P < 0.001). Ln_AU was significantly higher in 62 mg iodine/mL than in 111 or 170 mg iodine/mL (P < 0.001 for both). Ln_AU was significantly lower at a lumen diameter of 5.7 mm than 3.9 mm (P = 0.001) or 3.0 (P < 0.001).

CONCLUSION

Calcified plaque subtraction in DECT substantially underestimates measurements of lumen area. Higher enhancement in larger vessels ensures more accurate subtraction of calcified plaque.

Cardiovascular Imaging: The Past and the Future, Perspectives in Computed Tomography and Magnetic Resonance Imaging

Today's noninvasive imaging of the cardiovascular system has revolutionized the approach to various diseases and has substantially affected prognostic information. Cardiovascular magnetic resonance (MR) and computed tomographic (CT) imaging are at center stage of these approaches, although 5 decades ago, these technologies were unheard of. Both modalities had their inception in the 1970s with a primary focus on noncardiovascular applications. The technical development of the various decades, however, substantially pushed the envelope for cardiovascular MR and CT applications. Within the past 10-15 years, MR and CT technologies have pushed each other in cardiac applications; and without the "rival" modality, neither one would likely not have reached its potential today. This view on the history of MR and CT in the field of cardiovascular applications provides insight into the story of success of applications that once have been ideas only but are at prime time today.

Optimal Scanning Protocols for Dual-Energy CT Angiography in Peripheral Arterial Stents: An in Vitro Phantom Study

OBJECTIVE

To identify the optimal dual-energy computed tomography (DECT) scanning protocol for peripheral arterial stents while achieving a low radiation dose, while still maintaining diagnostic image quality, as determined by an in vitro phantom study.

METHODS

Dual-energy scans in monochromatic spectral imaging mode were performed on a peripheral arterial phantom with use of three gemstone spectral imaging (GSI) protocols, three pitch values, and four kiloelectron volts (keV) ranges. A total of 15 stents of different sizes, materials, and designs were deployed in the phantom. Image noise, the signal-to-noise ratio (SNR), different levels of adaptive statistical iterative reconstruction (ASIR), and the four levels of monochromatic energy for DECT imaging of peripheral arterial stents were measured and compared to determine the optimal protocols.

RESULTS

A total of 36 scans with 180 datasets were reconstructed from a combination of different protocols. There was a significant reduction of image noise with a higher SNR from monochromatic energy images between 65 and 70 keV in all investigated preset GSI protocols (p < 0.05). In addition, significant effects were found from the main effect analysis for these factors: GSI, pitch, and keV (p = 0.001). In contrast, there was significant interaction on the unstented area between GSI and ASIR (p = 0.015) and a very high significant difference between keV and ASIR (p < 0.001). A radiation dose reduction of 50% was achieved.

CONCLUSIONS

The optimal scanning protocol and energy level in the phantom study were GSI-48, pitch value 0.984, and 65 keV, which resulted in lower image noise and a lower radiation dose, but with acceptable diagnostic images.

Optimization of keV-settings in abdominal and lower extremity dual-source dual-energy CT angiography determined with virtual monoenergetic imaging

OBJECTIVES

To compare objective image quality indices in dual-energy CT angiography (DE-CTA) studies of the abdomen and lower extremity using conventional polyenergetic images (PEIs) and virtual monoenergetic images (MEIs) at different kiloelectron volt (keV) levels.

METHODS

We retrospectively evaluated 68 dual-source DE-CTA studies. 50 patients (42 men, 71 ± 10 years) underwent abdominal DE-CTA. 18 patients (13 men, 67 ± 10 years) underwent lower extremity DE-CTA. MEIs from 40 to 120 keV were reconstructed. Signal intensity, noise, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were assessed in infrarenal aorta, superior mesenteric, external iliac, femoral, popliteal, and lower leg arteries. Comparisons between MEIs and PEIs were performed with Dunnett's test.

RESULTS

222 arteries were evaluated. In abdominal arteries 70 keV MEIs showed statistically equal signal intensity, noise and CNR levels (+13%; +31%, -14% on average; all p>0.05) compared to PEIs; SNR was equal or slightly impaired (-7% on average; p<0.001-1.00). In lower extremity arteries 60 keV MEIs resulted in significantly higher signal intensity and CNR (+54%; +54% on average; all p<0.05) compared to PEIs at equal noise levels (+18% on average; all p>0.05) and equal or higher SNR (+49% on average; p<0.01-0.35).

CONCLUSIONS

Low-keV MEIs lead to equal or higher signal intensity and CNR compared to PEIs. In lower extremity DE-CTA, additional reconstruction of low-keV MEIs at 60 keV might increase diagnostic confidence.

Dual-energy CT: vascular applications

OBJECTIVE

Dual-energy CT permits a variety of image reconstructions for the depiction and characterization of vascular disease. Techniques include visualization of low- and high-peak-kilovoltage spectra image datasets and also material-specific reconstructions combining both low- and high-peak-kilovoltage data.

CONCLUSION

This article focuses on four main vascular areas: the aorta, the major visceral, lower limb, and cervical arteries. For each territory, the current status, potential advantages, and limitations of these techniques are described.

[Dual energy CT angiography of the carotid arteries: quality, bone subtraction, and radiation dosage using tube voltage 80/140 kV versus 100/140 kV]

OBJECTIVE

To study the differences in vascular image quality, bone subtraction, and dose of radiation of dual energy CT angiography of the supraaortic trunks using different tube voltages.

MATERIAL AND METHODS

We reviewed the CT angiograms of the supraaortic trunks in 46 patients acquired with a 128-slice dual source CT scanner using two voltage protocols (80/140 kV and 100/140 kV). The "head bone removal" tool was used for postprocessing. We divided the arteries into 15 segments. In each segment, we evaluated the image quality of the vessels and the effectiveness of bone removal in multiplanar reconstructions (MPR) and in maximum intensity projections (MIP) with each protocol, analyzing the trabecular and cortical bones separately. We also evaluated the dose of radiation received.

RESULTS

Of the 46 patients, 13 were studied using 80/140 kV and 33 with 100/140 kV. There were no significant differences between the two groups in age or sex. Image quality in four segments was better in the group examined with 100/140 kV. Cortical bone removal in MPR and MIP and trabecular bone removal in MIP were also better in the group examined with 100/140 kV. The dose of radiation received was significantly higher in the group examined with 100/140 kV (1.16 mSv with 80/140 kV vs. 1.59 mSv with 100/140 kV).

CONCLUSION

Using 100/140 kV increases the dose of radiation but improves the quality of the study of arterial segments and bone subtraction.

Subtraction coronary CT angiography for calcified lesions

One of the main problems in coronary angiography using 64-row computed tomography (CT) is that the presence of severe calcification interferes with the assessment of lesions, which reduces diagnostic accuracy and may even make assessment of some coronary artery segments impossible. With 320-row CT, it is possible to avoid this problem by performing subtraction coronary CT, which fully exploits the performance capabilities of the CT system. However, subtraction coronary CT has several limitations. When these limitations have been overcome, this technique is expected to become a useful method for assessing patients with severe calcification and evaluating coronary artery stents.

Subtraction CT angiography of the lower extremities: single volume subtraction versus multi-segmented volume subtraction

RATIONALE AND OBJECTIVES

To validate the hypothesis that a multisegmented approach during subtraction computed tomography (CT) angiography of the lower extremities can improve bone removal efficiency by suppressing regional motion.

MATERIALS AND METHODS

The institutional review board of our hospital approved this retrospective study. One hundred and one consecutive patients that had undergone the lower extremity CT angiography were included in this study. Subtraction CT angiography was performed using two different methods, namely, by single volume subtraction and by multisegmented volume subtraction. Multisegmented volume subtraction was conducted by dividing the whole volume of the CT data into three segments along the z axis of the lower extremities, performing a subtraction process for each segment, and combining segments to form as single subtracted volume. The bone removal efficiencies of the two methods was assessed by analyzing bone subtraction scores on maximum intensity projection (MIP) images for each bone segment in a blinded fashion. In addition, overall MIP image qualities were compared by displaying MIP images produced using the two methods side by side. Differences between bone subtraction scores were tested using Wilcoxon's signed rank test.

RESULTS

Multisegmented volume subtraction MIP images demonstrated significantly better bone removal for the following bone segments: pelvis (P < .0001), hip (P = .0002), thigh (P = .0258), knee (P = .0004), ankle (P = .0008), metatarsal bone (P < .0001), and toes (P < .0001). Overall bone subtraction score and subjective image qualities determined by performing side-by-side comparisons were better for the multisegmented volume subtraction method.

CONCLUSION

Bone removal performance and overall MIP image quality can be increased by adopting multisegmented volume subtraction during subtraction CT angiography of the lower extremities.

Dual- and multi-energy CT: approach to functional imaging

The energy spectrum of X-ray photons after passage through an absorber contains information about its elemental composition. Thus, tissue characterisation becomes feasible provided that absorption characteristics can be measured or differentiated. Dual-energy CT uses two X-ray spectra enabling material differentiation by analysing material-dependent photo-electric and Compton effects. Elemental concentrations can thereby be determined using three-material decomposition algorithms. In comparison to dual-energy CT used in clinical practice, recently developed energy-sensitive photon-counting detectors sample the material-specific attenuation curves at multiple energy levels and within narrow energy bands; the latter allows the detection of element-specific, k-edge discontinuities of the photo-electric cross section. Multi-energy CT imaging therefore is able to concurrently identify multiple materials with increased accuracy. These specific data on material distribution provide information beyond morphological CT, and approach functional imaging. This article reviews the principles of dual- and multi-energy CT imaging, hardware approaches and clinical applications.