Identification of a small thrombus in the left ventricle identified on iodine maps derived from dual-source photon-counting detector CT

Transthoracic echocardiography is the main imaging modality to diagnose left ventricular thrombus (LVT), but its efficacy in certain cases is suboptimal. We report a patient in whom an LVT, initially unidentified by transthoracic echocardiography, was successfully diagnosed with iodine maps derived from dual-source photon-counting detector CT (DS-PCD-CT). The 64-year-old male was admitted to our institution following myocardial infarction. Although TTE failed to detect this small LVT, iodine maps derived from CT angiography (which was conducted to evaluate the coronary artery stenosis) revealed its presence. Iodine maps derived from DS-PCD-CT collecting data with high temporal resolution are beneficial to diagnose LVTs.

Dual-Energy, Spectral and Photon Counting Computed Tomography for Evaluation of the Gastrointestinal Tract

The use of dual-energy computed tomography (CT) allows for reconstruction of energy- and material-specific image series. The combination of low-energy monochromatic images, iodine maps, and virtual unenhanced images can improve lesion detection and disease characterization in the gastrointestinal tract in comparison with single-energy CT.

Dual-Energy Computed Tomography Applications in Lung Cancer

This article examines the intrathoracic applications for dual-energy computed tomography (DECT), focusing on lung cancer. The topics covered include the image data sets, methods for iodine quantification, and clinical applications. The applications of DECT are to differentiate benign and malignant lung nodules, determining the grade of lung cancer and expression of ki-67 expression. Iodine quantification has role in assessment of treatment response in both the primary tumor and nodal metastases.

Spectral CT of the abdomen: Where are we now?

Spectral CT adds a new dimension to radiological evaluation, beyond assessment of anatomical abnormalities. Spectral data allows for detection of specific materials, improves image quality while at the same time reducing radiation doses and contrast media doses, and decreases the need for follow up evaluation of indeterminate lesions. We review the different acquisition techniques of spectral images, mainly dual-source, rapid kV switching and dual-layer detector, and discuss the main spectral results available. We also discuss the use of spectral imaging in abdominal pathologies, emphasizing the strengths and pitfalls of the technique and its main applications in general and in specific organs.

Renal Adiposity Does not Preclude Quantitative Assessment of Renal Function Using Dual-Energy Multidetector CT in Mildly Obese Human Subjects

RATIONALE AND OBJECTIVES

Multidetector computed tomography (MDCT) is useful for measuring in the research setting single-kidney perfusion and function using iodinated contrast time-attenuation curves. Obesity promotes deposition of intrarenal fat, which might decrease tissue attenuation and thereby interfere with quantification of renal function using MDCT. The purpose of this study was to test the hypothesis that background subtraction adequately accounts for intrarenal fat deposition in mildly obese human subjects during renal contrast enhanced dynamic CT.

MATERIALS AND METHODS

We prospectively recruited seventeen human subjects stratified as lean or mildly obese based on body mass index below or over 30 kg/m², respectively. Renal perfusion was quantified from CT-derived indicator-dilution curves after background subtraction. Dual-energy MDCT images were postprocessed to generate iodine and virtual-noncontrast datasets, and the ratios between kidney/aorta CT numbers and iodine values calculated as surrogates of renal function.

RESULTS

Subcutaneous adipose tissue was increased in obese subjects. Virtual-noncontrast maps revealed in obese patients a decrease in basal cortical and medullary attenuation. Overall, basal attenuation inversely correlated with body mass index, in line with renal fat deposition. Contrarily, the kidney/aorta CT attenuation (after background subtraction) and kidney/aorta iodine ratios were similar between lean and obese subjects and correlated directly. These observations show that following background subtraction, the CT number reliably reflects basal tissue attenuation.

CONCLUSION

Therefore, our findings support our hypothesis that background subtraction enables reliable assessment of kidney function in mildly obese subjects using MDCT, despite decreased basal attenuation due to renal adiposity.

Diagnostic value of spectral reconstructions in detecting incidental skeletal muscle metastases in CT staging examinations

Background

To investigate if iodine density overlay maps (IDO) and virtual monoenergetic images at 40 keV (VMI_40keV) acquired from spectral detector computed tomography (SDCT) can improve detection of incidental skeletal muscle metastases in whole-body CT staging examinations compared to conventional images.

Methods

In total, 40 consecutive cancer patients who underwent clinically-indicated, contrast-enhanced, oncologic staging SDCT were included at this retrospective study: 16 patients with n = 108 skeletal muscle metastases confirmed by prior or follow-up CT, ¹⁸F-FDG-PET, MRI or histopathology, and a control group of 24 patients without metastases. Four independent readers performed blinded, randomized visual detection of skeletal muscle metastases in conventional images, IDO and VMI_40keV, indicating diagnostic certainty for each lesion on a 5-point Likert scale. Quantitatively, ROI-based measurements of attenuation (HU) in conventional images and VMI_40keV and iodine concentration in IDO were conducted. CNR was calculated and receiver operating characteristics (ROC) analysis of quantitative parameters was performed.

Results

Regarding subjective assessment, IDO (63.2 (58.5–67.8) %) and VMI_40keV (54.4 (49.6–59.2) %) showed an increased sensitivity for skeletal muscle metastases compared to conventional images (39.8 (35.2–44.6) %). Specificity was comparable in VMI_40keV (69.8 (63.2–75.8) %) and conventional images (69.2 (60.6–76.9) %), while in IDO, it was moderately increased to 74.2 (65.3–78.4) %. Quantitative image analysis revealed that CNR of skeletal muscle metastases to circumjacent muscle was more than doubled in VMI_40keV (25.8 ± 11.1) compared to conventional images (10.0 ± 5.3, p ≤ 0.001). Iodine concentration obtained from IDO and HU acquired from VMI_40kev (AUC = 0.98 each) were superior to HU attenuation in conventional images (AUC = 0.94) regarding differentiation between healthy and metastatic muscular tissue (p ≤ 0.05).

Conclusions

IDO and VMI_40keV provided by SDCT improve diagnostic accuracy in the assessment of incidental skeletal muscle metastases compared to conventional CT.

Dual-Energy Computed Tomography: Physical Principles, Approaches to Scanning, Usage, and Implementation: Part 2

There are increasing applications and use of spectral computed tomography or dual-energy computed tomography (DECT) in neuroradiology and head and neck imaging in routine clinical practice. Part 1 of this 2-part review covered fundamental physical principles underlying DECT scanning and the different approaches for scanning. Part 2 focuses on important and practical considerations for implementing and using DECT in clinical practice, including a review of different images and reconstructions produced by these scanners and important and practical issues, ranging from image quality and radiation dose to workflow-related aspects of DECT scanning, that routinely come up during operationalization of DECT.

Intrarenal fat deposition does not interfere with the measurement of single-kidney perfusion in obese swine using multi-detector computed tomography

BACKGROUND

Altered vascular structure or function in several diseases may impair renal perfusion. Multi-detector computed tomography (MDCT) is a non-invasive tool to assess single-kidney perfusion and function based on dynamic changes in tissue attenuation during contrast media transit. However, changes in basal tissue attenuation might hamper these assessments, despite background subtraction. Evaluation of iodine concentration using the dual-energy (DECT) MDCT mode allows excluding effects of basal values on dynamic changes in tissue attenuation. We tested whether decreased basal kidney attenuation secondary to intrarenal fat deposition in swine obesity interferes with assessment of renal perfusion using MDCT.

METHODS

Domestic pigs were fed a standard (lean) or a high-cholesterol/carbohydrate (obese) diet (n = 5 each) for 16 weeks, and both kidneys were then imaged using MDCT/DECT after iodinated contrast injection. DECT images were post-processed to generate iodine and virtual-non-contrast (VNC) datasets, and the MDCT kidney/aorta CT number (following background subtraction) and DECT iodine ratios calculated during the peak vascular phase as surrogates of renal perfusion. Intrarenal fat was subsequently assessed with Oil-Red-O staining.

RESULTS

VNC maps in obese pigs revealed decreased basal cortical attenuation, and histology confirmed increased renal tissue fat deposition. Nevertheless, the kidney/aorta attenuation and iodine ratios remained similar, and unchanged compared to lean pigs.

CONCLUSIONS

Despite decreased basal attenuation secondary to renal adiposity, background subtraction allows adequate assessment of kidney perfusion in obese pigs using MDCT. These observations support the feasibility of renal perfusion assessment in obese subjects using MDCT.

Quantitative myocardial perfusion with stress dual-energy CT: iodine concentration differences between normal and ischemic or necrotic myocardium. Initial experience

OBJECTIVES

To determine whether the quantification of iodine with stress dual-energy computed tomography (DECT-S) allows for the discrimination between a normal and an ischemic or necrotic myocardium using magnetic resonance (MR) as a reference.

METHODS

This retrospective study was approved by the institutional review board, with waiver of informed consent. Thirty-six cardiac MR and DECT-S images from patients with suspected coronary artery disease were evaluated. Perfusion defects were visually determined, and myocardial iodine concentration was calculated by two observers using DECT colour-coded iodine maps. Iodine concentration differences were calculated using parametric tests. Receiver operating characteristic (ROC) curve analysis was conducted to estimate the optimal iodine concentration threshold for discriminating pathologic myocardium.

RESULTS

In total, 576 cardiac segments were evaluated. There were differences in mean iodine concentration (p < 0.001) between normal (2.56 ± 0.66 mg/mL), ischemic (1.98 ± 0.36 mg/dL) and infarcted segments (1.35 ± 0.57 mg/mL). A myocardium iodine concentration of 2.1 mg/mL represented the optimal threshold to discriminate between normal and pathologic myocardium (sensitivity 75 %, specificity 73.6 %, area under the curve 0.806). Excellent agreement was found in measured myocardium iodine concentration (intraclass correlation coefficient 0.814).

CONCLUSION

Cardiac DECT-S with iodine quantification may be useful to differentiate healthy and ischemic or necrotic myocardium.

KEY POINTS

• DECT-S allows for determination of myocardial iodine concentration as a quantitative perfusion parameter. • A high interobserver correlation exists in measuring myocardial iodine concentration with DECT-S. • Myocardial iodine concentration may be useful in the assessment of patients with CAD.

Correlation analysis of dual-energy CT iodine maps with quantitative pulmonary perfusion MRI

AIM: To correlate dual-energy computed tomography (DECT) pulmonary angiography derived iodine maps with parameter maps of quantitative pulmonary perfusion magnetic resonance imaging (MRI).

METHODS: Eighteen patients with pulmonary perfusion defects detected on DECT derived iodine maps were included in this prospective study and additionally underwent time-resolved contrast-enhanced pulmonary MRI [dynamic contrast enhanced (DCE)-MRI]. DCE-MRI data were quantitatively analyzed using a pixel-by-pixel deconvolution analysis calculating regional pulmonary blood flow (PBF), pulmonary blood volume (PBV) and mean transit time (MTT) in visually normal lung parenchyma and perfusion defects. Perfusion parameters were correlated to mean attenuation values of normal lung and perfusion defects on DECT iodine maps. Two readers rated the concordance of perfusion defects in a visual analysis using a 5-point Likert-scale (1 = no correlation, 5 = excellent correlation).

RESULTS: In visually normal pulmonary tissue mean DECT and MRI values were: 22.6 ± 8.3 Hounsfield units (HU); PBF: 58.8 ± 36.0 mL/100 mL per minute; PBV: 16.6 ± 8.5 mL; MTT: 17.1 ± 10.3 s. In areas with restricted perfusion mean DECT and MRI values were: 4.0 ± 3.9 HU; PBF: 10.3 ± 5.5 mL/100 mL per minute, PBV: 5 ± 4 mL, MTT: 21.6 ± 14.0 s. The differences between visually normal parenchyma and areas of restricted perfusion were statistically significant for PBF, PBV and DECT (P < 0.0001). No linear correlation was found between MRI perfusion parameters and attenuation values of DECT iodine maps (PBF: r = 0.35, P = 0.15; PBV: r = 0.34, P = 0.16; MTT: r = 0.41, P = 0.08). Visual analysis revealed a moderate correlation between perfusion defects on DECT iodine maps and the parameter maps of DCE-MRI (mean score 3.6, κ 0.45).

CONCLUSION: There is a moderate visual but not statistically significant correlation between DECT iodine maps and perfusion parameter maps of DCE-MRI.