Dual-energy CT after radiofrequency ablation of liver, kidney, and lung lesions: a review of features

Beyond Conventional CT: Role of Dual-Energy CT in Monitoring Response to Therapy in Abdominal Malignancies

In the era of precision medicine, imaging plays a critical role in evaluating treatment response to various oncologic therapies. For decades, conventional morphologic assessments using cross-sectional imaging have been the standard for monitoring the effectiveness of systemic and locoregional therapies in patients with cancer. However, the development of new functional imaging tools has widened the scope of imaging from mere response assessment to patient selection and outcome prediction. Dual-energy CT (DECT), known for its superior material differentiation capabilities, shows promise in enhancing treatment response evaluation. DECT-based iodine quantification methods are increasingly being investigated as surrogates for assessing tumor vascularity and physiology, which is particularly important in patients undergoing emerging targeted therapies. The purpose of this review article is to discuss the current and emerging role of DECT in assessing treatment response in patients with malignant abdominal tumors. Keywords: CT-Dual Energy, Transcatheter Tumor Therapy, Tumor Response, Iodine Uptake, Therapeutic Response © RSNA, 2025.

Imaging in interventional oncology, the better you see, the better you treat

Imaging and image processing is the fundamental pillar of interventional oncology in which diagnostic, procedure planning, treatment and follow-up are sustained. Knowing all the possibilities that the different image modalities can offer is capital to select the most appropriate and accurate guidance for interventional procedures. Despite there is a wide variability in physicians preferences and availability of the different image modalities to guide interventional procedures, it is important to recognize the advantages and limitations for each of them. In this review, we aim to provide an overview of the most frequently used image guidance modalities for interventional procedures and its typical and future applications including angiography, computed tomography (CT) and spectral CT, magnetic resonance imaging, Ultrasound and the use of hybrid systems. Finally, we resume the possible role of artificial intelligence related to image in patient selection, treatment and follow-up.

Update on Image-Guided Thermal Lung Ablation: Society Guidelines, Therapeutic Alternatives, and Postablation Imaging Findings

Percutaneous image-guided thermal ablation (IGTA) has been endorsed by multiple societies as a safe and effective lung-preserving treatment for primary lung cancer and metastases involving the lung and chest wall. This article reviews the role of IGTA in the care continuum of patients with thoracic neoplasms and discusses strategies to identify the optimal local therapy considering patient and tumor characteristics. The advantages and disadvantages of percutaneous thermal ablation compared to surgical resection and stereotactic body radiotherapy are summarized. Principles of radiofrequency ablation, microwave ablation, and cryoablation, as well as the emerging use of transbronchial thermal ablation, are described. Specific considerations are presented regarding the role of thermal ablation for early-stage non-small cell lung cancer (NSCLC), multifocal primary NSCLC, pulmonary metastases, salvage of recurrent NSCLC after surgery or radiation, and pain palliation for tumors involving the chest wall. Recent changes to professional society guidelines regarding the role of thermal ablation in the lung, including for treatment of oligometastatic disease, are highlighted. Finally, recommendations are provided for imaging follow-up after thermal ablation of lung tumors, accompanied by examples of expected postoperative findings and patterns of disease recurrence.

Virtual Noncontrast Imaging of the Liver Using Photon-Counting Detector Computed Tomography: A Systematic Phantom and Patient Study

OBJECTIVES

The aim of this study was to assess the accuracy of virtual noncontrast (VNC) images of the liver in a phantom and patients using dual-source photon-counting detector computed tomography (PCD-CT).

MATERIALS AND METHODS

An anthropomorphic abdominal phantom with a liver insert containing liver parenchyma (1.4 mgI/mL) and 19 liver lesions (iodine content 0-5 mgI/mL) was imaged on a clinical dual-source PCD-CT (tube voltage 120 kV) and in the dual-energy mode on a dual-source energy-integrating detector (EID) CT (tube voltage combinations, 80/Sn150 kV, 90/Sn150 kV, and 100/Sn150 kV). Rings of fat-equivalent material were added to the phantom to emulate 3 sizes (small, medium, large). Each setup was imaged at 3 different radiation doses (volume CT dose index: 5, 10, and 15 mGy). Virtual noncontrast images were reconstructed and CT attenuation was measured in each lesion and liver parenchyma. The absolute error of CT attenuation (VNCerror) was calculated using the phantom specifications as reference. In addition, 15 patients with hypodense liver lesions who were clinically scanned on PCD-CT were retrospectively included. Attenuation values in lesions and liver parenchyma in VNC images reconstructed from portal venous phase CT were compared with true noncontrast images. Statistical analysis included analysis of variance with post hoc t tests and generalized linear models to assess the impact of various variables (dose, patient size, base material, iodine content, and scanner/scan mode) on quantification accuracy.

RESULTS

In the phantom, the overall mean VNCerror for PCD-CT was 4.1 ± 3.9 HU. The overall mean VNCerror for EID-CT was 7.5 ± 5, 6.3 ± 4.7, and 6.7 ± 4.8 HU for 80/Sn150 kV, 90/Sn150 kV, and 100/Sn150 kV, respectively, with the VNCerror of EID-CT being significantly higher at all tube voltage settings (P < 0.001), even after adjusting for dose, size, iodine content of the lesion, and attenuation of base material. For PCD-CT, a smaller phantom size was associated with higher quantification accuracy (P = 0.007-0.046), whereas radiation dose did not impact accuracy (P > 0.126). For EID-CT, but not for PCD-CT, VNCerror increased with lesion iodine content (P < 0.001). In patients, there was no difference in attenuation measured on true noncontrast and VNC images (P = 0.093), with a mean VNCerror of 3.7 ± 2.2 HU.

CONCLUSIONS

Photon-counting detector CT allows for the reconstruction of VNC images of the liver both in a phantom and in patients with accurate attenuation values, being independent of dose, attenuation of base material, and liver iodine content.

Predicting the coagulation volume induced by microwave ablation of hepatocellular carcinoma: the role of deposited energy, ex-vivo bovine liver charts and central hyperdense area on post-treatment CT

PURPOSE

To study the correlation between the overall coagulation zone (A) attained in percutaneous microwave ablation (MWA) of hepatocellular carcinomas (HCC) and: (1) the hyperdense zone (C) visible in the central part of zone A on post-treatment unenhanced CT scans; (2) the deposited energy; (3) the coagulation zones observed on ex-vivo bovine liver.

MATERIALS AND METHODS

The post-procedural computed tomography (CT) scans of HCCs treated with a single energy deployment through the same 2450 MHz MWA system were retrospectively analyzed, retrieving the dimensions of A and C zones and the deposited energy (E). Ex-vivo bovine liver MWA with the same system were performed and analyzed to determine the same quantities by gross-pathologic examination and CT imaging.

RESULTS

A total of 101 HCC treatments were analyzed. The average coagulation volumes increased linearly with deposited energy (1.11 cc/kJ, R² = 0.90, 4.2 kJ ≤ E ≤ 48 kJ), similarly to ex-vivo findings (1.38 cc/kJ, R² =0.97, 7.2 kJ ≤ E ≤ 144 kJ). The long axis (L) and short axis (D) of zones A and C held a fairly constant ratio both in-vivo (L_C/L_A=0.43 ± 0.13; D_C/D_A=0.42 ± 0.10) and ex-vivo (L_C/L_A = 0.49 ± 0.07; D_C/D_A = 0.28 ± 0.06).

CONCLUSIONS

The average dimensions of the ablation zone induced by the considered system on HCC increase linearly with the deposited energy and are fairly well predicted by the corresponding ex-vivo dimensions. The ratio between each linear dimension of A and C zones was found to be roughly constant over a large deposited energy span, both ex-vivo and in-vivo.

Development of an Integrated C-Arm Interventional Imaging System With a Strip Photon Counting Detector and a Flat Panel Detector

Modern interventional x-ray systems are often equipped with flat-panel detector-based cone-beam CT (FPD-CBCT) to provide tomographic, volumetric, and high spatial resolution imaging of interventional devices, iodinated vessels, and other objects. The purpose of this work was to bring an interchangeable strip photon-counting detector (PCD) to C-arm systems to supplement (instead of retiring) the existing FPD-CBCT with a high quality, spectral, and affordable PCD-CT imaging option. With minimal modification to the existing C-arm, a 51×0.6 cm² PCD with a 0.75 mm CdTe layer, two energy thresholds, and 0.1 mm pixels was integrated with a Siemens Artis Zee interventional imaging system. The PCD can be translated in and out of the field-of-view to allow the system to switch between FPD and PCD-CT imaging modes. A dedicated phantom and a new algorithm were developed to calibrate the projection geometry of the narrow-beam PCD-CT system and correct the gantry wobbling-induced geometric distortion artifacts. In addition, a detector response calibration procedure was performed for each PCD pixel using materials with known radiological pathlengths to address concentric artifacts in PCD-CT images. Both phantom and human cadaver experiments were performed at a high gantry rotation speed and clinically relevant radiation dose level to evaluate the spectral and non-spectral imaging performance of the prototype system. Results show that the PCD-CT system has excellent image quality with negligible artifacts after the proposed corrections. Compared with FPD-CBCT images acquired at the same dose level, PCD-CT images demonstrated a 53% reduction in noise variance and additional quantitative imaging capability.

Spectral detector CT applications in advanced liver imaging

OBJECTIVE

Spectral detector CT (SDCT) has many applications in advanced liver imaging. If appropriately utilized, this technology has the potential to improve image quality, provide new diagnostic information, and allow for decreased radiation dose. The purpose of this review is to familiarize radiologists with the uses of SDCT in liver imaging.

CONCLUSION

SDCT has a variety of post-processing techniques, which can be used in advanced liver imaging and can significantly add value in clinical practice.

Value of spectral detector computed tomography for the early assessment of technique efficacy after microwave ablation of hepatocellular carcinoma

OBJECTIVES

To investigate whether virtual monoenergetic images (VMI) and iodine maps derived from spectral detector computed tomography (SDCT) improve early assessment of technique efficacy in patients who underwent microwave ablation (MWA) for hepatocellular carcinoma (HCC) in liver cirrhosis.

METHODS

This retrospective study comprised 39 patients with 49 HCC lesions treated with MWA. Biphasic SDCT was performed 7.7±4.0 days after ablation. Conventional images (CI), VMI and IM were reconstructed. Signal- and contrast-to-noise ratio (SNR, CNR) in the ablation zone (AZ), hyperemic rim (HR) and liver parenchyma were calculated using regions-of-interest analysis and compared between CI and VMI between 40-100 keV. Iodine concentration and perfusion ratio of HR and residual tumor (RT) were measured. Two readers evaluated subjective contrast of AZ and HR, technique efficacy (complete vs. incomplete ablation) and diagnostic confidence at determining technique efficacy.

RESULTS

Attenuation of liver parenchyma, HR and RT, SNR of liver parenchyma and HR, CNR of AZ and HR were significantly higher in low-keV VMI compared to CI (all p<0.05). Iodine concentration and perfusion ratio differed significantly between HR and RT (all p<0.05; e.g. iodine concentration, 1.6±0.5 vs. 2.7±1.3 mg/ml). VMI50keV improved subjective AZ-to-liver contrast, HR-to-liver contrast, visualization of AZ margin and vessels adjacent to AZ compared to CI (all p<0.05). Diagnostic accuracy for detection of incomplete ablation was slightly higher in VMI50keV compared to CI (0.92 vs. 0.89), while diagnostic confidence was significantly higher in VMI50keV (p<0.05).

CONCLUSIONS

Spectral detector computed tomography derived low-keV virtual monoenergetic images and iodine maps provide superior early assessment of technique efficacy of MWA in HCC compared to CI.

Use of dual-energy CT for renal mass assessment

Although dual-energy CT (DECT) may prove useful in a variety of abdominal imaging tasks, renal mass evaluation represents the area where this technology can be most impactful in abdominal imaging compared to routinely performed contrast-enhanced-only single-energy CT exams. DECT post-processing techniques, such as creation of virtual unenhanced and iodine density images, can help in the characterization of incidentally discovered renal masses that would otherwise remain indeterminate based on post-contrast imaging only. The purpose of this article is to review the use of DECT for renal mass assessment, including its benefits and existing limitations. KEY POINTS: • If DECT is selected as the scanning mode for most common abdominal protocols, many incidentally found renal masses can be fully triaged within the same exam. • Virtual unenhanced and iodine density DECT images can provide additional information when renal masses are discovered in the post-contrast-only setting. • For renal mass evaluation, virtual unenhanced and iodine density DECT images should be interpreted side-by-side to troubleshoot pitfalls that can potentially lead to erroneous interpretation.

Virtual non-contrast for evaluation of liver parenchyma and vessels: results from 25 patients using multi-phase spectral-detector CT

BACKGROUND

In abdominal imaging, contrast-enhanced computed tomography (CT) examinations are most commonly applied; however, unenhanced examinations are still needed for several clinical questions but require additional scanning and radiation exposure.

PURPOSE

To evaluate accuracy of virtual non-contrast (VNC) from arterial and venous phase spectral-detector CT (SDCT) scans compared to true-unenhanced (TNC) images for the evaluation of liver parenchyma and vessels.

MATERIAL AND METHODS

A total of 25 patients undergoing triphasic SDCT examinations were included. VNC was reconstructed from arterial and venous phases and compared to TNC images. Quantitative image analysis was performed by region of interest (ROI)-based assessment of mean and SD of attenuation (HU) in each liver segment, spleen, portal vein, common hepatic artery, and abdominal aorta. Subjectively, iodine subtraction and diagnostic assessment were rated on 5-point Likert scales.

RESULTS

Attenuation and image noise measured in the liver from VNC were not significantly different from TNC (TNC: 54.6 ± 10.8 HU, VNC arterial phase: 55.7 ± 10.8 HU; VNC venous phase: 58.3 ± 10.0 HU; P > 0.05). VNC also showed accurate results regarding attenuation and image noise for spleen, portal vein, and abdominal aorta. Only iodine subtraction in the common hepatic artery in the arterial phase was insufficient which was confirmed by the subjective reading. Apart from that, subjective reading showed accurate iodine subtraction and comparable diagnostic assessment.

CONCLUSION

VNC from the arterial and venous phases were very similar to TNC yielding mostly negligible differences in attenuation, image noise, and diagnostic utility. Inadequate iodine subtraction occurred in hepatic arteries in the arterial phase.

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.

Imaging after radiofrequency ablation of renal tumors

The number of percutaneous radiofrequency ablation procedures performed for renal tumors is progressively increasing worldwide. Periodic imaging follow-up has the double role to guarantee the treatment efficacy over time and to early detect any possible complication. Tumor size reductions, as well as the appearance of the characteristic ‘halo sign’, are normal findings that represent good ablative outcomes. However the most reliable factor of ablation efficacy remains the total absence of contrast enhancing zones within the ablated area. The aim of this article is to illustrate the typical aspect of an effective radiofrequency ablation treatment, which are the imaging findings that may suggest the presence of residual tumoral tissue and which are the main early and late procedural complications.

Use of Dual-Energy Computed Tomography for Evaluation of Genitourinary Diseases

Since its clinical inception a decade ago, dual-energy computed tomography has expanded the array of computed tomography imaging tools available to the practicing abdominal radiologist. Of note, diagnostic solutions for imaging-based evaluation of genitourinary diseases, foremost kidney calculi and renal tumors characterization, represent the apogee applications of dual-energy computed tomography in abdominal imaging. This article reviews clinical applications of dual-energy computed tomography for the assessment of genitourinary diseases.

Multi-detector CT: Liver protocol and recent developments

Multi-detector computed tomography is today the workhorse in the evaluation of the vast majority of patients with known or suspected liver disease. Reasons for that include widespread availability, robustness and repeatability of the technique, time-efficient image acquisitions of large body volumes, high temporal and spatial resolution as well as multiple post-processing capabilities. However, as the technique employs ionizing radiation and intravenous iodine-based contrast media, the associated potential risks have to be taken into account. In this review article, liver protocols in clinical practice are discussed with emphasis on optimisation strategies. Furthermore, recent developments such as perfusion CT and dual-energy CT and their applications are presented.

Dual-Energy Computed Tomography in Genitourinary Imaging

Reignited by innovations in scanner engineering and software design, dual-energy computed tomography (CT) has come back into the clinical radiology arena in the last decade. Possibilities for noninvasive in vivo characterization of genitourinary disease, especially for renal stones and renal masses, have become the pinnacle offerings of dual-energy CT for body imaging in clinical practice. This article renders a state-of-the-art review on clinical applications of dual-energy CT in genitourinary imaging.

Optimization of window settings for virtual monoenergetic imaging in dual-energy CT of the liver: A multi-reader evaluation of standard monoenergetic and advanced imaged-based monoenergetic datasets

OBJECTIVES

To evaluate optimal window settings for display of virtual monoenergetic reconstructions in third-generation dual-source, dual-energy computed tomography (DECT) of the liver.

METHODS

Twenty-nine subjects were prospectively evaluated with DECT in arterial (AP) and portal venous (PVP) phases. Three reconstructed datasets were calculated: standard linearly-blended (LB120), 70-keV standard virtual monoenergetic (M70), and 50-keV advanced image-based virtual monoenergetic (M50+). Two readers assessed optimal window settings (width and level, W/L), establishing a mean for each reconstruction which was used for a blinded assessment of liver lesions.

RESULTS

The optimal W/L for M50+ were significantly higher for both AP (W=429.3 ± 44.6 HU, L=129.4 ± 9.7 HU) and PVP (W=376.1 ± 14.2HU, L=146.6 ± 7.0 HU) than for LB120 (AP, W=215.9 ± 16.9 HU, L=82.3 ± 9.4 HU) (PVP, W=173.4 ± 8.9 HU, L=69.3 ± 6.0 HU) and M70 (AP, W=247.1 ± 22.2 HU, L=72.9 ± 6.8 HU) (PVP, W=232.0 ± 27.9 HU, L=91.6 ± 14.4 HU). Use of the optimal window setting for M50+ vs. LB120 resulted in higher sensitivity (AP, 100% vs. 86%; PVP, 96% vs. 63%).

CONCLUSIONS

Application of dedicated window settings results in improved liver lesion detection rates in advanced image-based virtual monoenergetic DECT when customized for arterial and portal venous phases.