Influence of Radiation Dose, Photon Energy, and Reconstruction Kernel on rho/z Analysis in Spectral Computer Tomography: A Phantom Study

BACKGROUND/AIM

The effective atomic number (Z_eff) and electron density relative to water (ρ_e or Rho) of elements can be derived in dual-energy computed tomography (DECT). The aim of this phantom study was to investigate the effect of different photon energies, radiation doses, and reconstruction kernels on Z_eff and Rho measured in DECT.

MATERIALS AND METHODS

An anthropomorphic head phantom including five probes of known composition was scanned under three tube-voltage combinations in DECT: Sn140/100 kV, 140/80 kV and Sn140/80 kV with incremented radiation doses. Raw data were reconstructed with four reconstruction kernels (I30, I40, I50, and I70). Rho and Z_eff were measured for each probe for all possible combinations of scan and reconstruction parameters.

RESULTS

DECT-based Rho and Z_eff closely approached the reference values with a mean and maximum error of 1.7% and 6.8%, respectively. Rho was lower for 140/80 kV compared with Sn140/100 kV and Sn140/80 kV with differences being 0.009. Z_eff differed among all tube voltages with the most prominent difference being 0.28 between 140/80 kV and Sn140/100 kV. Z_eff was lower in I70 compared with those of I30 and I40 with a difference of 0.07. Varying radiation dose yielded a variation of 0.0002 in Rho and 0.03 in Z, both considered negligible in practice.

CONCLUSION

DECT comprises a feasible method for the extraction of material-specific information. Slight variations should be taken into account when different radiation doses, photon energies, and kernels are applied; however, they are considered small and in practice not crucial for an effective tissue differentiation.

Influence of Radiation Dose and Reconstruction Kernel on Fat Fraction Analysis in Dual-energy CT: A Phantom Study

BACKGROUND/AIM

The quantitative evaluation of fat tissue, mainly for the determination of liver steatosis, is possible by using dual-energy computed tomography. Different photon energy acquisitions allow for estimation of attenuation coefficients. The effect of variation in radiation doses and reconstruction kernels on fat fraction estimation was investigated.

MATERIALS AND METHODS

A six-probe-phantom with fat concentrations of 0%, 20%, 40%, 60%, 80%, and 100% were scanned in Sn140/100 kV with radiation doses ranging between 20 and 200 mAs before and after calibration. Images were reconstructed using iterative kernels (I26,Q30,I70).

RESULTS

Fat fractions measured in dual-energy computed tomography (DECT) were consistent with the 20%-stepwise varying actual concentrations. Variation in radiation dose resulted in 3.1% variation of fat fraction. Softer reconstruction kernel (I26) underestimated the fat fraction (-9.1%), while quantitative (Q30) and sharper kernel (I70) overestimated fat fraction (10,8% and 13,1, respectively).

CONCLUSION

The fat fraction in DECT approaches the actual fat concentration when calibrated to the reconstruction kerneö. Variation of radiation dose caused an acceptable 3% variation.

Detection and characterization of COVID-19 findings in chest CT: Feasibility and applicability of an AI-based software tool

ABSTRACT

The COVID-19 pandemic has challenged institutions' diagnostic processes worldwide. The aim of this study was to assess the feasibility of an artificial intelligence (AI)-based software tool that automatically evaluates chest computed tomography for findings of suspected COVID-19.Two groups were retrospectively evaluated for COVID-19-associated ground glass opacities of the lungs (group A: real-time polymerase chain reaction positive COVID patients, n = 108; group B: asymptomatic pre-operative group, n = 88). The performance of an AI-based software assessment tool for detection of COVID-associated abnormalities was compared with human evaluation based on COVID-19 reporting and data system (CO-RADS) scores performed by 3 readers.All evaluated variables of the AI-based assessment showed significant differences between the 2 groups (P < .01). The inter-reader reliability of CO-RADS scoring was 0.87. The CO-RADS scores were substantially higher in group A (mean 4.28) than group B (mean 1.50). The difference between CO-RADS scoring and AI assessment was statistically significant for all variables but showed good correlation with the clinical context of the CO-RADS score. AI allowed to predict COVID positive cases with an accuracy of 0.94.The evaluated AI-based algorithm detects COVID-19-associated findings with high sensitivity and may support radiologic workflows during the pandemic.

Quantifying image quality in chest computed tomography angiography: Evaluation of different contrast-to-noise ratio measurement methods

BACKGROUND

Contrast-to-noise ratio is used to objectively evaluate image quality in chest computed tomography angiography (CTA). Different authors define and measure contrast-to-noise ratio using different methods.

PURPOSE

To summarize and evaluate the different contrast-to-noise ratio calculation formulas in the current literature.

MATERIAL AND METHODS

A systematic review of the recent literature for studies using contrast-to-noise ratio was performed. Contrast-to-noise ratio measurement methods reported by the different authors were recorded and reproduced in three patients who underwent chest CTA in our department for exploring variations among the different measurement methods.

RESULTS

The search resulted in 109 articles, of which 26 were included. The studies involved 69 different measurements and overall, three different formula patterns. In all three, aorta and pulmonary arteries comprised the objects of interest in the numerator. In the denominator, standard deviation of the attenuation of the object of interest itself or of another background were used to reflect image noise. Some authors averaged the ratio values at different levels to obtain global ratio values. Using the object of interest itself for image noise calculation in the denominator compared to the usage of another background caused the most prominent variances of contrast-to-noise ratio between the two different protocols used for the reproduction of the measurements.

CONCLUSION

We recommend using the standard deviation of the attenuation of a background indicator as image noise rather than the object of interest itself for more reliable and comparative values. Global contrast-to-noise ratios based on averaging the values of different measurement levels should be avoided.

Preoperative chest computed tomography in emergency surgery during COVID-19 pandemic

BACKGROUND

The COVID-19 pandemic challenges the recommendations for patients' preoperative assessment for preventing severe acute respiratory syndrome coronavirus type 2 transmission and COVID-19-associated postoperative complications and morbidities.

PURPOSE

To evaluate the contribution of chest computed tomography for preoperatively assessing patients who are not suspected of being infected with COVID-19 at the time of referral.

METHODS

Candidates for emergency surgery screened via chest computed tomography from 8 to 27 April 2020 were retrospectively evaluated. Computed tomography images were analysed for the presence of COVID-19-associated intrapulmonary changes. When applicable, laboratory and recorded clinical symptoms were extracted.

RESULTS

Eighty-eight patients underwent preoperative chest computed tomography; 24% were rated as moderately suspicious and 11% as highly suspicious on computed tomography. Subsequent reverse transcription polymerase chain reaction (RT-PCR) was performed for seven patients, all of whom tested negative for COVID-19. Seven patients showed COVID-19-associated clinical symptoms, and most were classified as being mildly to moderately severe as per the clinical classification grading system. Only one case was severe. Four cases underwent RT-PCR with negative results.

CONCLUSION

In a cohort without clinical suspicion of COVID-19 infection upon referral, preoperative computed tomography during the COVID-19 pandemic can yield a high suspicion of infection, even if the patient lacks clinical symptoms and is RT-PCR-negative. No recommendations can be made based on our results but contribute to the debate.

Prevalence of calcified epiglottis in postmortem computed tomography. Is there a correlation to failed endotracheal intubation?

OBJECTIVES

Calcification of the epiglottis is a normal physiological degenerative process, although it can also be a consequence of infection or trauma. There are three possible forensically relevant consequences from epiglottic calcification: misinterpretation as foreign bodies, dysphagia as a major contributing factor to aspiration, and association with difficult intubation or a misplaced ventilation tube. It is the aim of this study (I) to inquire about the prevalence of epiglottic calcification in postmortem CT in general and (II) to investigate whether calcification of the epiglottis is linked to a higher incidence of failed endotracheal intubation.

METHODS

We retrospectively analysed 2930 consecutive cases in postmortem CT at the Institute of Forensic Medicine.

RESULTS

The prevalence of epiglottic calcification was 4.1%. Higher age and male sex are associated with an increased risk of epiglottic calcification. There was no calcification of the epiglottis in the cases with misplacement of the ventilation tube in the esophagus.

CONCLUSIONS

To verify the result of our study, that is, the calcification of the epiglottis is not linked to a higher incidence of failed endotracheal intubation, it might be reasonable to repeat this study with a more representative study population. The high interindividual variations of calcified epiglottis could be used for identification.

Evaluation of the mediastinal-thoracic volume ratio on postmortem computed tomography

Objectives

The aim of this study was to measure the mediastinal-thoracic volume ratio (CTR_VOL) on PMCT as a more accurate version of traditional CTR, in order to assess the terminal positional relationship between the heart and lungs in the different causes of death with regard to age, gender, BMI, cardiomegaly, and lung expansion.

Materials

Two hundred fifty consecutive postmortem cases with pre-autopsy PMCT and full forensic autopsy were retrospectively evaluated. The lungs and the mediastinum were manually segmented on the PMCT data and the correspondent volumes were estimated in situ. CTR_VOL was calculated as the ratio of the mediastinal to the thoracic volume. The volume measurements were repeated by the same rater for the evaluation of the intrarater reliability. Age, gender, body weight and height, heart weight at autopsy, and cause of death were retrieved from the autopsy reports. Presence of lung expansion was radiologically evaluated in situ.

Results

CTR_VOL was positively associated with age and BMI but not with gender and was higher for cardiomegaly compared to normal hearts, lower for asphyxiation-related deaths compared to cardiac deaths and intoxications, and lower for cases with lung expansion. The intrarater reliability was excellent for the calculated volumes of both lungs and mediastinum.

Conclusion

The results of the present study support CTR_VOL as a tool to assess the relationship between the heart and lungs in situ, which differs significantly between the studied cause of death categories.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00414-021-02593-0.

Diagnostic accuracy of postmortem computed tomography for bleeding source determination in cases with hemoperitoneum

Aim

The aim of this retrospective study was to determine the accuracy of postmortem computed tomography and different radiological signs for the determination of the bleeding source in cases with hemoperitoneum confirmed at autopsy.

Methods

Postmortem computed tomography data of consecutive cases with hemoperitoneum confirmed at autopsy were reviewed by two raters, blinded to the autopsy findings. The determination of possible bleeding sources was based on the presence of the sentinel clot sign, blood or sedimented blood surrounding an organ, intraparenchymal abnormal gas distribution, and parenchymal disruption. The bleeding source and the cause of hemoperitoneum (traumatic, surgical, natural, or resuscitation) as reported in the autopsy report were noted. The survival intervals of the deceased were calculated when information about the time of an incident related to death was available in the autopsy reports.

Results

Eighty-five cases were included in the study. Postmortem computed tomography showed 79% sensitivity and 92.1% specificity for the detection of the bleeding source. The sentinel clot sign was associated with surgical or natural causes of hemoperitoneum and longer survival intervals. Sedimented blood around the bleeding source was associated with resuscitation. Abnormal gas distribution within organs and combination of multiple radiological signs provided higher sensitivity.

Conclusion

Postmortem computed tomography provides moderate sensitivity and high specificity for determining the bleeding source in cases with hemoperitoneum. Different PMCT signs are associated with different causes of hemoperitoneum and survival intervals.

Left myocardial wall measurements on postmortem imaging compared to autopsy

PURPOSE

The aims of this study were, firstly, to determine the relationship of left ventricular wall thickness (LVWT) measurements between postmortem computed tomography (PMCT) and postmortem magnetic resonance imaging (PMMR) and, secondly, to assess the utility of postmortem imaging for LVWT measurements compared to autopsy.

MATERIALS AND METHODS

All cases ≥18years old, with postmortem interval ≤4days, cardiac PMCT, PMMR, and full forensic autopsy, were reviewed in our database retrospectively. Exclusion criteria were gas accumulations in the myocardial wall and cardiac trauma. LVWT on PMCT and PMMR was assessed. The measurements were repeated by the same rater after 2months. Autopsy reports were reviewed, and LVWT and pericardial fluid volume measured at autopsy were noted. Pericardial fluid volume >50ml was determined positive for pericardial effusion.

RESULTS

A total of 113 cases were included in the study. Twelve cases had pericardial effusion. Intrarater reliability for imaging based LVWT was excellent. LVWT (free wall) was significantly larger on PMCT (18.3mm) compared to PMMR (17.6mm), but these measurements correlated positively. LVWT (anterior wall) was significantly larger on PMMR (15mm) than at autopsy (14mm), and these measurements also correlated positively. Pericardial effusions led to larger differences between PMMR and autopsy measurements, however without statistical significance.

DISCUSSION

There exist discrepancies between LVWT as measured on postmortem imaging and at autopsy. Specialists should be aware in order to not misinterpret imaging measurements.

Approaching pulmonary fat embolism on postmortem computed tomography

PURPOSE

Pulmonary fat embolism (PFE) is a relevant diagnosis playing a role as a sign of vitality or a cause of death. Its severity is assessed according to histological grading systems like that of Falzi. The aim of this study was to determine the utility of unenhanced postmortem computed tomography (PMCT) for PFE diagnosis based on the detection of fat layers.

METHODS

Consecutive cases with PMCT and autopsy were studied retrospectively. The case group consisted of cases with positive PFE, and the control group included cases with negative PFE. Three observers independently assessed PMCT data for fat layers in the pulmonary trunk and the right and left pulmonary artery. For cases with fat layers, autopsy protocols were assessed for the cause of death, relation to trauma, and undertaken resuscitation measures.

RESULTS

Eight hundred thirty cases were included: 366 PFE positive cases (144 of Falzi grade 1, 63 of 1.5, 99 of 2, 28 of 2.5, and 32 of 3) and 464 PFE negative cases. Interrater reliabilities varied between substantial and almost perfect, and discrepancies were solved according to majority. Eighteen cases showed fat layers on PMCT (2 controls-traumatic instantaneous deaths-, 16 PFE positive cases). PMCT showed low sensitivity but high specificity for PFE diagnosis. The layers were located at the same position in the pulmonary trunk directly adjacent to the pulmonary valve distal to the right ventricle.

CONCLUSION

Fat layer on PMCT is a rare finding but relates to PFE diagnosis, especially of severe histological grade. It is to be expected in a typical position within the pulmonary trunk.

Death by hanging: a retrospective case-control investigation of the intervertebral disc vacuum phenomenon on PMCT

During hanging gravitational forces affect the spine. Intervertebral vacuum phenomenon (VP) implies that gas accumulations in the discs are caused by degeneration of the spine and trauma. It was hypothesized that VP detected on postmortem computed tomography (PMCT) has a higher incidence in hanging deaths, which can be correlated to age, degenerative spinal changes and type of hanging (complete-incomplete). Secondly, it was investigated whether the presence of Simon's bleedings is related to hanging type and VP on PMCT. A retrospective hanging case-control study of 72 cases was conducted. PMCT data were evaluated by two observers for the presence of VP and its localization within the thoracic and lumbar discs, and for any degenerative changes of the spine. Autopsy protocols were assessed for the presence of Simon's bleedings during autopsy. VP did not statistically differ among hanging and control cases but it was statistically correlated to complete hanging, increasing age and degenerative spinal changes. Centrally located VP within the discs was correlated to hanging, especially complete hanging, and younger ages, contrary to control cases that showed gas at the disc periphery. Simon's bleedings were correlated with complete hanging and centrally located VP. Centrally located VP within the discs increases the probability for complete hanging, while increasing age and degenerative changes reduce this probability. Intervertebral VP is multifactorial radiological entity. The presence of centrally located VP can indicate that hanging could be considered as an alternative mechanism of death and that great forces and loads may have affected the spine perimortem, especially with decreasing age and when Simon's bleedings are present.