Assessment of anemia during CT pulmonary angiography

In vitro blood sample assessment: investigating correlation of laboratory hemoglobin and spectral properties of dual-energy CT measurements (ρ/Z)

OBJECTIVES

Our study comprised a single-center retrospective in vitro correlation between spectral properties, namely ρ/Z values, derived from scanning blood samples using dual-energy computed tomography (DECT) with the corresponding laboratory hemoglobin/hematocrit (Hb/Hct) levels and assessed the potential in anemia-detection.

METHODS

DECT of 813 patient blood samples from 465 women and 348 men was conducted using a standardized scan protocol. Electron density relative to water (ρ or rho), effective atomic number (Zeff), and CT attenuation (Hounsfield unit) were measured.

RESULTS

Positive correlation with the Hb/Hct was shown for ρ (r-values 0.37-0.49) and attenuation (r-values 0.59-0.83) while no correlation was observed for Zeff (r-values -0.04 to 0.08). Significant differences in attenuation and ρ values were detected for blood samples with and without anemia in both genders (p value < 0.001) with area under the curve ranging from 0.7 to 0.95. Depending on the respective CT parameters, various cutoff values for CT-based anemia detection could be determined.

CONCLUSION

In summary, our study investigated the correlation between DECT measurements and Hb/Hct levels, emphasizing novel aspects of ρ and Zeff values. Assuming that quantitative changes in the number of hemoglobin proteins might alter the mean Zeff values, the results of our study show that there is no measurable correlation on the atomic level using DECT. We established a positive in vitro correlation between Hb/Hct values and ρ. Nevertheless, attenuation emerged as the most strongly correlated parameter with identifiable cutoff values, highlighting its preference for CT-based anemia detection.

CLINICAL RELEVANCE STATEMENT

By scanning multiple blood samples with dual-energy CT scans and comparing the measurements with standard laboratory blood tests, we were able to underscore the potential of CT-based anemia detection and its advantages in clinical practice.

KEY POINTS

Prior in vivo studies have found a correlation between aortic blood pool and measured hemoglobin and hematocrit. Hemoglobin and hematocrit correlated with electron density relative to water and attenuation but not Zeff. Dual-energy CT has the potential for additional clinical benefits, such as CT-based anemia detection.

Anemia detection and quantification in contrast-enhanced CT scans on a novel photon-counting detector CT: A prospective proof-of-concept study

PURPOSE

To correlate CT values of the blood pool on VNC series with serum hemoglobin values for the detection of anemia in oncologic patients undergoing contrast-enhanced PCD-CT scans.

METHODS

This prospective study (NCT04989192) included consecutive oncologic patients undergoing contrast-enhanced CT on a novel PCD-CT system between 08/2021 and 01/2022. The interval between complete blood count (CBC) and CT scan acquisition had to be no more than seven days. CT-values of the blood pool were measured on 70 keV VMI series (CT-values(BP)70keV) and on VNC series (CT-values(BP)VNC) at five anatomic positions (left atrium, left ventricle, main pulmonary artery, ascending and descending aorta) and averaged per patient. Pearson correlation analyses and ROC analyses were performed to identify relations between CT-values(BP)VNC, CBC parameters, and degrees of anemia as defined by the WHO (no anemia, mild, moderate, severe anemia).

RESULTS

A total of 329 patients (age 68 ± 12 years; 200 men) were included. CT-values(BP)VNC showed a strong linear correlation to serum hemoglobin (r2 = 0.80, p <.001) and hematocrit (r2 = 0.76, p <.001) and were significantly different between anemia subgroups in both women and men (ΔHU: 3.5-11.4; all p <.01). ROC analyses yielded high diagnostic performance for the identification of patients without anemia, patients without and with mild anemia, and patients with severe anemia using gender-specific cutoffs for CT-value(BP)VNC (all AUC's > 0.90).

CONCLUSIONS

The spectral information inherent in PCD-CT acquisitions allows the detection and quantification of anemia in contrast-enhanced CT acquisitions of oncologic patients with high diagnostic accuracy.

Detection of Low Blood Hemoglobin Levels on Pulmonary CT Angiography: A Feasibility Study Combining Dual-Energy CT and Machine Learning

OBJECTIVES

To evaluate if dual-energy CT (DECT) pulmonary angiography (CTPA) can detect anemia with the aid of machine learning.

METHODS

Inclusion of 100 patients (mean age ± SD, 51.3 ± 14.8 years; male-to-female ratio, 42/58) who underwent DECT CTPA and hemoglobin (Hb) analysis within 24 h, including 50 cases with Hb below and 50 controls with Hb ≥ 12 g/dL. Blood pool attenuation was assessed on virtual noncontrast (VNC) images at eight locations. A classification model using extreme gradient-boosted trees was developed on a training set (n = 76) for differentiating cases from controls. The best model was evaluated in a separate test set (n = 24).

RESULTS

Blood pool attenuation was significantly lower in cases than controls (p-values < 0.01), except in the right atrium (p = 0.06). The machine learning model had sensitivity, specificity, and accuracy of 83%, 92%, and 88%, respectively. Measurements at the descending aorta had the highest relative importance among all features; a threshold of 43 HU yielded sensitivity, specificity, and accuracy of 68%, 76%, and 72%, respectively.

CONCLUSION

VNC imaging and machine learning shows good diagnostic performance for detecting anemia on DECT CTPA.

Feasibility of thoracic CT in assessing anemia for aplastic anemia patients undergoing allogeneic hematopoietic stem cell transplantation

BACKGROUND

Anemia is an important clinical symptom for aplastic anemia (AA) patients who are suffered with peripheral pancytopenia.

OBJECTIVE

To evaluate the accuracy of diagnosing anemia with non-invasive chest computed tomography (CT) for AA patients.

METHODS

The CT attenuation of left ventricular (LV) cavity and interventricular septum (IVS) on unenhanced thoracic CT images of AA patients are retrospectively analyzed, including 84 AA patients in pre-transplant and 1-month (n = 82), 2-month (n = 72), 3-month (n = 75), 6-month (n = 74) and 12-month (n = 70) followed patients in post-transplant. The difference (IVS-LV) and ratio (LV/IVS) of the CT attenuation between LV cavity and interventricular septum are calculated. Serum hemoglobin is estimated within 24 hours of CT imaging. The CT attenuations of IVS-LV and LV/IVS are correlated with hemoglobin, and their variation tendency is analyzed during the treatment of a-HSCT. A receiver operating characteristic (ROC) curve analysis is then performed for the diagnosis of anemia.

RESULTS

The CT attenuations of IVS-LV and LV/IVS well correlate with hemoglobin (r = -0.618 and 0.628, respectively, P <  0.001). The variation tendency of IVS-LV and LV/IVS is similar to that of hemoglobin with opposite directions during one-year follow-up of a-HSCT. When a threshold of CT attenuation of IVS-LV and LV/IVS is set at 11.5HU and 0.77, respectively, both the sensitivity and specificity in diagnosing anemia are good (74.7% and 73.8% in CT attenuation of IVS-LV; 77.4% and 70.4% in LV/LVS, respectively).

CONCLUSIONS

Both CT attenuation of LV/IVS and IVS-LV had similar accuracy in diagnosing anemia for AA patients. The non-invasive chest CT can offer a new possibility to complementarily evaluate anemia for AA patients in the diagnostic radiology reports.

Low-dose CT from myocardial perfusion SPECT/CT allows the detection of anemia in preoperative patients

BACKGROUND

To assess whether low-dose CT for attenuation correction of myocardial perfusion single-photon emission computed tomography (SPECT) allows for identification of anemic patients and grading anemia severity.

METHODS AND RESULTS

Patients who underwent a preoperative blood-test and low-dose CT scan, as a part of a cardiac SPECT exam, between 01 January 2015 and 31 December 2017 were enrolled in this retrospective study. Hemoglobin (Hb) levels and hematocrit were derived from clinical records. CT images were visually assessed (qualitative analysis) for the detection of inter-ventricular septum sign (IVSS) and aortic rim sign (ARS) and quantitative analysis were performed. The diagnostic accuracy for detecting anemia was compared using Hb values as the standard of reference. A total of 229 patients were included (110 with anemia; 57 mild; 46 moderate; 7 severe). The AUC of IVSS and ARS were 0.830 and 0.669, respectively (p<0.0001). The quantitative analysis outperformed ARS and IVSS; (AUC of 0.893, p=0.29). The optimal anemia cut-off using Youden index was 4.5 HU.

CONCLUSION

Quantitative analysis derived from low-dose CT images, as a part of cardiac SPECT exams, have a diagnostic accuracy similar to that of hematocrit for the detection of anemia and may allow discriminating different anemia severities.

Comparison between thoracic low-dose computed tomography and conventional-dose computed tomography in evaluating anemia: A preliminary study in a Chinese screening cohort

Purpose

To investigate and evaluate the value of thoracic low dose computed tomography (LDCT) scan in the diagnosis of anemia.

Materials and methods

661 patients who received thoracic computed tomography (CT) examination and underwent a peripheral blood examination were retrospectively included. 341 patients underwent conventional dose CT (CDCT), and 320 patients underwent LDCT. Regions of interest (ROI) were placed on the left ventricular cavity (LV), descending aorta (DAo), and interventricular septum (IVS). The corresponding CT attenuation was measured, and the CT attenuation difference between LV and IVS (IVS-LV) and between DAo and IVS (IVS-DAo) was calculated, respectively. One-way analysis of variance (ANOVA) and linear regression were performed to analyze the relationship between these indicators and Hb levels. The receiver operating characteristic (ROC) curve was used to evaluate prediction performance.

Results

Both attenuation on LDCT and CDCT showed significant differences between the healthy group and the anemic group (P &lt; 0.05). In the LDCT group, the LV and DAo were more relevant with the hemoglobin (Hb) level (correlation coefficient 0.618 and 0.602) than other indicators, with AUCs of 0.815 (95% CI: 0.763–0.868) and 0.803 (95% CI: 0.747–0.859), respectively. The linear regression formulas for Hb level with the LV and DAo were 19.14 + 0.15 × HU [95% CI: (16.52, 21.75) + (0.12, 0.17) × HU] and 19.46 + 0.16 × HU [95% CI: (16.55, 22.36) + (0.13, 0.18) × HU], respectively. Youden’s index indicated that 37.5 HU and 38.5 HU were the best thresholds to diagnose anemia for LV and DAo, respectively. In the CDCT group, the LV and IVS-LV got obviously higher correlation coefficients (0.813 and 0.812), with AUCs of 0.831 (95% CI: 0.786–0.877) and 0.851 (95% CI: 0.808–0.894), respectively. The optimal thresholds for LV and IVS-LV were 40.5 HU and 9.5 HU, respectively.

Conclusion

In LDCT examinations, an approximation of Hb level and detecting of anemia can be conducted based on simple attenuation measurements.

The Value of Diffuse Splenic and Hepatic 18F-FDG Uptake on PET/CT in Diagnosing Patients with Anemia

Objective

Anemia is a disease with a negative impact on the progression and prognosis of tumor diseases and usually diagnosed by blood tests. Imaging examination has been used as an alternative method to diagnose anemia in addition to blood tests for patients who cannot tolerate blood draw (such as those with severe coagulopathy). The purpose of this study was to investigate the role of diffuse splenic and hepatic ¹⁸F-FDG uptake on PET/CT in anemia, by analyzing the correlation between the hemoglobin level and diffuse splenic and hepatic as well as marrow ¹⁸F-FDG uptakes in patients who underwent PET/CT.

Materials and Methods

Forty four patients who underwent a peripheral blood examination within 2 days of a ¹⁸F-FDG-PET/CT in our hospital from March 2020 to March 2021 were included. The standardized uptake value (SUV) of the spleen, liver, and marrow were measured, including the maximum value (SUVmax) and the mean value (SUVmean), and the CT value (CTV) of the left ventricular (LV) cavity was measured, including the maximum value (CTVmax) and the mean value (CTVmean). The relation between these measurements and the blood hemoglobin level were analyzed.

Results

Our analysis revealed that the hemoglobin level was negatively correlated with the SUVmax of the spleen (P ≤ 0.01, R = −0.385), SUVmean of the spleen (P ≤ 0.01, R = −0.395), SUVmax of the liver (P ≤ 0.05, R = −0.365), and SUVmean of the liver (P ≤ 0.05, R = −0.315). The hemoglobin level was positively correlated with CTVmax of the LV cavity (P ≤ 0.05, R = 0.33) and CTVmean of the LV cavity (P ≤ 0.05, R = 0.382), while no statistically significant correlation between the hemoglobin level and the SUV of marrow was observed (P > 0.05).

Conclusion

Our study revealed a negative correlation between the hemoglobin level and spleen SUV as well as liver SUV, and a positive correlation between the hemoglobin level and CTV of the LV cavity. These findings may provide potential indictors for the imaging diagnosis of anemia, which has important clinical significance in certain clinical scenarios including the evaluation of anemia status in patients who cannot tolerate blood draws and retrospective clinical studies based on patient imaging data.

Prediction of anemia on enhanced computed tomography of the thorax using virtual non-contrast reconstructions

To determine if anemia can be predicted on enhanced computed tomography (CT) examinations of the thorax using virtual non-contrast (VNC) images, in order to support clinicians especially in diagnosing primary asymptomatic patients in daily routine.In this monocentric study, 100 consecutive patients (50 with proven anemia), who underwent a contrast-enhanced CT examination of the thorax due to various indications were included. Attenuation was measured in the descending thoracic aorta, the intraventricular septum, and the left ventricle cavity both in the conventional contrast-enhanced and in the VNC images.Two experienced radiologists annotated the delineation of a dense interventricular septum or a hyperattenuating aortic wall sign for all patients.Hemoglobin levels were then correlated with the measured attenuation values, as well as the visualization of the aortic wall or interventricular septum.Good correlation was shown between hemoglobin levels and CT attenuation values of the left ventricular cavity (r = .59), aorta (r = .56), and ratio between left ventricular cavity and the intraventricular septum (r = .57). Receiver operating characteristic curve revealed ≤ 36.5 hounsfield units (left ventricular cavity) as the threshold for diagnosing anemia. Predicting anemia by visualization of a hyperattenuating aortic wall or a dense interventricular septum yielded a specificity of 98% and 92%, respectively.Predicting anemia on enhanced CT examinations using VNC is feasible. A threshold value of ≤ 36.5 hounsfield units (left ventricular cavity) best defines anemia. Aortic wall or interventricular septum visualization on VNC is a specific anemia indicator.

Potential of high dimensional radiomic features to assess blood components in intraaortic vessels in non-contrast CT scans

BACKGROUND

To assess the potential of radiomic features to quantify components of blood in intraaortic vessels to non-invasively predict moderate-to-severe anemia in non-contrast enhanced CT scans.

METHODS

One hundred patients (median age, 69 years; range, 19-94 years) who received CT scans of the thoracolumbar spine and blood-testing for hemoglobin and hematocrit levels ± 24 h between 08/2018 and 11/2019 were retrospectively included. Intraaortic blood was segmented using a spherical volume of interest of 1 cm diameter with consecutive radiomic analysis applying PyRadiomics software. Feature selection was performed applying analysis of correlation and collinearity. The final feature set was obtained to differentiate moderate-to-severe anemia. Random forest machine learning was applied and predictive performance was assessed. A decision-tree was obtained to propose a cut-off value of CT Hounsfield units (HU).

RESULTS

High correlation with hemoglobin and hematocrit levels was shown for first-order radiomic features (p < 0.001 to p = 0.032). The top 3 features showed high correlation to hemoglobin values (p) and minimal collinearity (r) to the top ranked feature Median (p < 0.001), Energy (p = 0.002, r = 0.387), Minimum (p = 0.032, r = 0.437). Median (p < 0.001) and Minimum (p = 0.003) differed in moderate-to-severe anemia compared to non-anemic state. Median yielded superiority to the combination of Median and Minimum (p(AUC) = 0.015, p(precision) = 0.017, p(accuracy) = 0.612) in the predictive performance employing random forest analysis. A Median HU value ≤ 36.5 indicated moderate-to-severe anemia (accuracy = 0.90, precision = 0.80).

CONCLUSIONS

First-order radiomic features correlate with hemoglobin levels and may be feasible for the prediction of moderate-to-severe anemia. High dimensional radiomic features did not aid augmenting the data in our exemplary use case of intraluminal blood component assessment. Trial registration Retrospectively registered.

Evaluating anemia using contrast-enhanced spectral detector CT of the chest in a large cohort of 522 patients

Objectives

The blood of patients with anemia demonstrates distinctly lower attenuation in unenhanced CT images. However, the frequent usage of intravenous contrast hampers evaluation of anemia. Spectral detector computed tomography (SDCT) allows for reconstruction of virtual non-contrast images (VNC) from contrast-enhanced data (CE). The purpose of this study was to evaluate whether VNC allow for prediction of anemia.

Methods

Five hundred twenty-two patients with CE-SDCT of the chest and accessible serum hemoglobin (HbS) were retrospectively included. Patients were assigned to three groups (severe anemia, moderate/mild anemia, and healthy) based on recent lab tests (≤ 7 days) for HbS following gender and the WHO definition of anemia. CT attenuation was determined using two ROI in the left ventricular lumen and one ROI in the descending thoracic aorta. ROI were placed on CE and copied to VNC. ANOVA, linear regression, and receiver operating characteristics were used for statistic evaluation.

Results

Average HbS was 11.6 ± 2.4 g/dl. Attenuation on VNC showed significant differences between healthy patients, patients with mild/moderate anemia, and severely anemic patients (all p ≤ 0.05). Applying cutoffs of 39.2/37.6 HU and 33.6/32.7 HU allowed to differentiate between healthy, mild/moderately, and severely anemic men/women (AUC 0.857/0.833 and 0.879/0.932). A linear relationship between HbS and attenuation on VNC was established (r² = 0.54, HbS = − 0.875 + 0.329 × HU).

Conclusions

An approximation of HbS and presence of anemia can be conducted based on simple attenuation measurements in contrast-enhanced SDCT examinations enabled by VNC imaging.

Key Points

• While the attenuation of blood is a previously described biomarker for anemia in non-contrast images, virtual non-contrast images from spectral detector CT circumvent this limitation and allow for diagnosis of anemia in contrast-enhanced scans.

• Attenuation of blood in virtual non-contrast images derived from spectral detector CT shows a moderate correlation to serum hemoglobin levels.

• Presence of anemia be estimated in virtual non-contrast images using proposed cutoffs of 39.2 HU and 37.6 HU for men and women, respectively, to differentiate between healthy and anemic patients.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00330-020-07497-y.

Automatic quantification of the myocardial extracellular volume by cardiac computed tomography: Synthetic ECV by CCT

BACKGROUND

The quantification of extracellular volume fraction (ECV) by Cardiac Computed Tomography (CCT) can identify changes in the myocardial interstitium due to fibrosis or infiltration. Current methodologies require laboratory blood hematocrit (Hct) measurement - which complicates the technique. The attenuation of blood (HU_blood) is known to change with anemia. We hypothesized that the relationship between Hct and HU_blood could be calibrated to rapidly generate a synthetic ECV without formally measuring Hct.

METHODS

The association between Hct and HU_blood was derived from forty non-contrast thoracic CT scans using regression analysis. Synthetic Hct was then used to calculate synthetic ECV, and in turn compared with ECV using blood Hct in a validation cohort with mild interstitial expansion due to fibrosis (aortic stenosis, n = 28, ECV_CT = 28 ± 4%) and severe interstitial expansion due to amyloidosis (n = 27; ECV_CT = 54 ± 11%, p < 0.001). For histological validation, synthetic ECV was correlated with collagen volume fraction (CVF) in a separate cohort with aortic stenosis (n = 18). All CT scans were performed at 120 kV and 160 mAs.

RESULTS

HU_blood was a good predictor of Hct (R² = 0.47; p < 0.01), with the regression model (Hct = [0.51 * HU_blood] + 17.4) describing the association. Synthetic ECV correlated well with conventional ECV (R² = 0.96; p < 0.01) with minimal bias and 2SD difference of 5.7%. Synthetic ECV correlated as well as conventional ECV with histological CVF (both R² = 0.50, p < 0.01). Finally, we implemented an automatic ECV plug-in for offline analysis.

CONCLUSION

Synthetic ECV by CCT provides instantaneous quantification of the myocardial extracellular space without the need for blood sampling.

Factors Affecting Attenuation of Dural Sinuses on Noncontrasted Computed Tomography Scan

BACKGROUND AND PURPOSE

Noncontrasted computed tomography (NCCT) is used as the initial neuroimaging test of choice for patients who present with new-onset neurological symptoms. An apparently hyperattenuated venous sinus may lead to the suspicion of cerebral venous sinus thrombosis (CVST). Improved understanding of all factors that can affect attenuation of dural sinuses can guide triage of patients to or from further investigations of suspected CVST. The purpose of this retrospective study was to assess the effect of different factors including hematocrit (HCT), hemoglobin (Hb), age, BUN/Cr ratio (blood urea nitrogen-to-creatinine ratio), and gender on the attenuation of dural sinuses on brain NCCT.

METHODS

A total of 1293 patients with neurological symptoms who presented to the emergency department were included in this study. For each patient, clinical assessment, laboratory investigations, and brain NCCT were reviewed. For each brain NCCT, the average attenuation of superior sagittal sinus and both right and left sigmoid sinuses was measured.

RESULTS

Positive significant correlations were found between average attenuation of dural sinuses on one hand and each of age, Hb, and HCT on the other hand. No significant correlation was found between average attenuation and BUN/Cr ratio. Gender discrepancy was also significant as higher attenuation was found in men.

CONCLUSION

Age, gender, and Hb levels are the main factors that should be taken into account upon the assessment of dural sinuses on brain NCCT. The highest normal attenuation is predicted in an elderly polycythemic man and the lowest is predicted in a young anemic woman.