Suspected pulmonary embolism: enhancement of pulmonary arteries at deep-inspiration CT angiography--influence of patent foramen ovale and atrial-septal defect

[Single-phase Pulmonary Arteriovenous Separation CT Protocol with Estimated Time of Arrival Method Using 3rd Generation Dual Source CT: Its Success Rate of Pulmonary Arteriovenous Separation in Our Experience of 223 Cases]

We retrospectively investigated the success rate of pulmonary arteriovenous separation in a single-phase computed tomography (CT) protocol using the estimated time of arrival (ETA) method. A total of 223 patients who underwent a single-phase CT protocol using the ETA method for pulmonary arteriovenous separation were included in the analysis. Dual source CT (SOMATOM Force, SIEMENS) was used for imaging. The tube voltage was 80 kVp, and the scan mode was turbo flash spiral mode. CT values of main pulmonary artery (MPA), peripheral pulmonary artery (pPA), peripheral pulmonary vein (pPV), left atrium (LA), ascending aorta (AAo) and descending aorta (DAo) were measured. When the difference in CT values on the central side was 100 Hounsfield unit (HU) or more, it was judged that the separation was successful. The mean CT values were 671.9±154 HU for MPA, 424.4±81.2 HU for LA, 551.1±142.6 HU for pPA, 351.6±94.0 HU for pPV, 362.2±75.8 HU for AAo, and 282.7±83.7 HU for DAo. The mean difference in CT values of the pulmonary artery and vein was 247.5±138.9 HU on the central side and 199.5±133.0 HU on the peripheral side. There were 90.1% of cases where the difference in CT values on the central side was 100 HU or more. In addition, a strong positive correlation (r=0.849, p<0.001) was found between the CT value of MPA and the CT value difference on the central side. The success rate of pulmonary arteriovenous separation by the ETA method, which is a method that enables stable pulmonary arteriovenous separation, was 90.1%.

Incidence of transient interruption of contrast (TIC) - A retrospective single-centre analysis in CT pulmonary angiography exams acquired during inspiratory breath-hold with the breathing command: "Please inspire gently!"

Objectives

To assess the occurrence of transient interruption of contrast (TIC) phenomenon in pulmonary computed tomography angiography (CTPA) exams performed in inspiratory breath-hold after patients were told to inspire gently.

Methods

In this retrospective single-centre study, CTPA exams of 225 consecutive patients scanned on a 16-slice CT scanner system were analysed. A-priori to measurements, exams were screened for inadequate pulmonary artery contrast due to incorrect bolus tracking or failure of i.v. contrast administration. Those exams were excluded. Attenuation values in the thoracic aorta and in the pulmonary trunk were assessed in duplicate measurements (M1 and M2) and the aorto-pulmonary density ratio was calculated. An aorto-pulmonary ratio > 1 with still contrast inflow being visible within the superior vena cava was defined as TIC.

Results

3 patients were excluded due to incorrect bolus tracking. Final analysis was performed in 222 patients (mean age 65 ± 19 years, range 18 to 99 years). Mean density in the pulmonary trunk was 275±17 HU, in the aorta 208 ± 15 HU. Mean aorto-pulmonary ratio was 0.81± 0.29. 48 patients (21.6%) had an aorto-pulmonary ratio >1. Correlation of mean aorto-pulmonary ratio and age was: -0.213 (p = 0.001). Age was not significantly different for an aorto-pulmonary ratio >1 vs. ≤1 (p = 0.122). Both in M1 and M2, 33/222 patients presented with absolute HU values of < 200 HU within the pulmonary artery. In M1 measurements, 24 of these 33 patients (72%) fulfilled TIC criteria (M2: 25/33 patients (75%)).

Conclusions

TIC is a common phenomenon in CTPA studies with inspiratory breath-hold commands after patients were told to inspire gently with an incidence of 22% in our retrospective cohort. Occurrence of TIC shows a significant negative correlation with increasing age and disproportionately often occurs in patients with lower absolute contrast density values within their pulmonary arteries.

Computed Tomography Angiographic Assessment of Acute Chest Pain

Acute chest pain is a leading cause of Emergency Department visits. Computed tomography angiography plays a vital diagnostic role in such cases, but there are several common challenges associated with the imaging of acute chest pain, which, if unrecognized, can lead to an inconclusive or incorrect diagnosis. These imaging challenges fall broadly into 3 categories: (1) image acquisition, (2) image interpretation (including physiological and pathologic mimics), and (3) result communication. The aims of this review are to describe and illustrate the most common challenges in the imaging of acute chest pain and to provide solutions that will facilitate accurate diagnosis of the causes of acute chest pain in the emergency setting.

We Built This House; It's Time to Move in: Leveraging Existing DICOM Structure to More Completely Utilize Readily Available Detailed Contrast Administration Information

The Digital Imaging and Communications in Medicine (DICOM) standard is the universal format for interoperability in medical imaging. In addition to imaging data, DICOM has evolved to support a wide range of imaging metadata including contrast administration data that is readily available from many modern contrast injectors. Contrast agent, route of administration, start and stop time, volume, flow rate, and duration can be recorded using DICOM attributes [1]. While this information is sparsely and inconsistently recorded in routine clinical practice, it could potentially be of significant diagnostic value. This work will describe parameters recorded by automatic contrast injectors, summarize the DICOM mechanisms available for tracking contrast injection data, and discuss the role of such data in clinical radiology.

CT angiography for pulmonary embolism detection: the effect of breathing on pulmonary artery enhancement using a 64-row detector system

BACKGROUND

Computed tomography pulmonary angiography (CTPA) is used most often in routine clinical practice for the assessment of a suspected pulmonary embolism. The diagnostic accuracy relies on sufficient contrast enhancement.

PURPOSE

To evaluate whether image acquisition during shallow breathing can improve the image quality in patients with insufficient contrast enhancement during breath-hold examinations.

MATERIAL AND METHODS

A total of 2786 CT pulmonary angiographies, acquired on a 64-row CT during deep-inspiration breath-hold, were reviewed. Twenty-four examinations were considered non-diagnostic due to poor contrast enhancement in the pulmonary arteries (PA), although they showed preserved vascular enhancement of the superior vena cava (SVC) and the ascending aorta (AO). Eleven flawed CTPA examinations, including severe breathing artifacts and incorrect triggering were excluded. In 13 of the remaining patients, the examination was repeated during shallow breathing. Vascular contrast enhancement was compared between both scans by measuring the relative enhancement within the SVC, the main PA, and the AO. Image quality was scored by two, clinically experienced radiologists. The values are given as median and [25th;75th] quartile.

RESULTS

There was a significant difference in the CT values for the PA between the repeated scans (P = 0.0002, Wilcoxon test), and with the CTPA in deep-inspiration showing a median enhancement of 97 HU (59-173), compared with 303 HU (239-385) in the CTPA acquired during free breathing. The differences for both the AO (P = 0.54) and the SVC (P = 0.78) were not significant. Scoring for the attenuation quality rose significantly (P = 0.0002) and no severe motion artifacts were detected on either scans.

CONCLUSION

If there is insufficient pulmonary artery enhancement during CTPA, attenuation of the pulmonary arteries can be improved by acquisition during shallow breathing and is without significant loss of the overall diagnostic image quality.

Has "respiratory coaching" before deep inspiration an impact on the incidence of transient contrast interruption during pulmonary CT angiography?

Purpose

To evaluate if respiratory coaching performed prior to CT pulmonary angiography (CTPA) image acquisition has an impact on the occurrence of transient interruption of contrast (TIC) phenomenon.

Materials and methods

Two hundred and thirty-one consecutive patients with suspected pulmonary embolism (PE) were referred for CTPA. They were randomised into two groups, with or without respiratory coaching (groups A and B, respectively). Those patients who were deemed not able to be coached were not randomised and were assigned to a third group (C). Two radiologists evaluated the degree of enhancement of the pulmonary arteries and the presence and grade of TIC. The χ² test was used to compare differences among groups in occurrence and grade of this phenomenon.

Results

There were no significant differences in the presence of any grade of TIC among the three groups, with 30 positive cases (32%) in group A, 33 (35%) in group B, and 12 (27%) in group C (P = 0.61). When TIC was graded and divided into significant or not, the different groups also did not differ significantly.

Conclusion

Performing respiratory coaching before CTPA had no statistically significant effect on the incidence and severity of TIC in this prospective randomised study.

Main Messages

• Significant transient interruption of contrast appears in 12% of pulmonary CT angiograms.

• Severe transient interruption of contrast leading to nondiagnostic tests appears in 2% of studies.

• In our study respiratory coaching has no impact on the incidence of transient interruption of contrast.

Image quality of computed tomographic pulmonary angiography for suspected pulmonary embolus in patients with diffuse interstitial lung disease

PURPOSE

To investigate the effect of diffuse interstitial lung disease (DILD) on the image quality of computed tomographic pulmonary angiography (CTPA).

MATERIALS AND METHODS

The study group comprised 130 patients with DILD who underwent CTPA between April 2005 and April 2009. One hundred and thirty patients without significant parenchymal lung disease were used as a control group. Contrast enhancement of pulmonary arteries in the left upper lobe and right lower lobe was evaluated to the sub-subsegmental level both subjectively and objectively. The global and lobar extents of interstitial lung disease were also estimated in the study group. Subjective assessment was performed by 2 observers, initially independently and subsequently by consensus in cases of discordance.

RESULTS

At the sub-subsegmental level, the number of patients with adequately opacified arteries was significantly lower in the DILD group (29.2% left upper lobe, 36.2% right lower lobe) compared with the control group (78.5% left upper lobe, 89.2% right lower lobe) (P<0.001). Subjective image quality scores of the sub-subsegmental arteries were strongly correlated with mean vascular attenuation values at this level (P<0.001) but not to the global or lobar extent of lung parenchymal disease. There was no clinically significant difference in image quality (either subjectively or objectively) between the DILD and control groups in the subsegmental and more proximal arterial branches.

CONCLUSIONS

In the majority of patients with DILD, CTPA image quality is sufficient only to the subsegmental level. Emboli at the sub-subsegmental level, which may have greater clinical significance in patients with DILD than in those without, are unlikely to be excluded using CTPA.

Haemodynamic findings on cardiac CT in children with congenital heart disease

In patients with congenital heart disease, haemodynamic findings demonstrated on cardiac CT might provide useful hints for understanding the haemodynamics of cardiac defects. In contrast to morphological features depicted on cardiac CT, such haemodynamic findings on cardiac CT have not been comprehensively reviewed in patients with congenital heart disease. This article describes normal haemodynamic phenomena of cardiovascular structures and various abnormal haemodynamic findings with their mechanisms and clinical significance on cardiac CT in patients with congenital heart disease.

[Chest CT: spectrum of normal findings]

A fundamental issue in the interpretation of chest CT lies in the ability to determine normality. Technical advances have resulted in an increasing number of submillimeter sections which in turn has resulted in the identification of a large number of minor abnormalities with no significant pathophysiological consequence. These images should be properly interpreted in order to avoid unnecessary follow-up examinations and radiation exposure. Often they are due to respiratory or cardiac motion artifacts. Others are explained by aging, anatomic variants, physiological phenomenon or tobacco use. These borderline imaging features detected on chest CT are described according to the main anatomical compartments of the thorax: lung and vessels, airways, pleura and chest wall, mediastinum and heart.

Waiting to exhale: salvaging the nondiagnostic CT pulmonary angiogram by using expiratory imaging to improve contrast dynamics

We attempted to investigate whether computed tomography pulmonary angiography (CTPA) in the expiratory phase can improve contrast enhancement of the pulmonary arteries and mitigate the effect of inspiratory transient attenuation artifact, potentially salvaging nondiagnostic studies. Eighteen patients with indeterminate inspiratory CTPA, despite proper contrast bolus were studied. Patients were rescanned in expiration using the same contrast bolus and scanning parameters. The attenuation of each pulmonary arterial segment, superior and inferior vena cava, and atria and ventricles during the two phases of respiration was measured independently by three radiologists. All pulmonary segments were evaluated for filling defects during the two phases. In addition, the studies were graded for diagnostic quality of enhancement and probable impact on management. A statistically significant increase in pulmonary arterial enhancement was seen during expiration from the pulmonary trunk to the segmental pulmonary arteries (P < 0.001) and for the inferior vena cava, the right atrium, and the ventricle. The incidence of nondiagnostic inspiratory studies ranged from 89 to 100%, depending on the observer. All studies were upgraded to fully acceptable diagnostic quality with follow-up expiratory imaging (P < 0.0001). Expiratory phase imaging was observed to have diagnostic impact in 78 to 88% of cases, with overall good to moderate interobserver agreement. In one case, pulmonary embolism was detected on the expiratory scan, which was not seen on the inspiratory scan. Expiratory imaging for nondiagnostic CTPA improves pulmonary arterial enhancement and improves diagnostic quality of CTPA by eliminating transient attenuation artifact, thus facilitating more accurate diagnosis and providing earlier treatment of pulmonary embolism.

Transient Interruption of Contrast on CT Pulmonary Angiography

PURPOSE

To test the hypothesis that a transient interruption of contrast is the result of an increase in flow of unopacified blood from the inferior vena cava (IVC) by comparing the relative IVC contribution to the right side of the heart in cases and age-matched and sex-matched controls.

MATERIALS AND METHODS

This retrospective study was approved by our internal review board. Of 234 consecutive patients who had both CT pulmonary angiography and a close follow-up diagnostic pulmonary angiogram, or in one case CT pulmonary angiography, 7 cases were identified which contained a transient interruption of contrast. The study group included 2 men and 5 women. The age range was 37 to 77 years (mean 61.3 y +/-13.3). The artifact consists of a segment of the pulmonary arteries which demonstrates poor blood enhancement between areas of increased attenuation both proximally and distally. Hounsfield units (HU) measurements were made in the areas of decreased attenuation, the areas of higher attenuation both proximally and distally, the superior vena cava, IVC, right atrium (RA), and right ventricle (RV). The relative IVC contribution was calculated by equating density in the RA and RV to a weighted average of the densities of the superior vena cava and IVC. Age-matched and sex-matched controls and a 2-tailed paired t test were used.

RESULTS

In the patients with the artifact, the average relative IVC contributions to the RA and RV are 80.1% and 79.5%, respectively. In the control patients, the values for the RA and RV are 52.8% (P=0.02) and 55.5% (P=0.02), respectively.

CONCLUSIONS

Transient interruption of contrast of the pulmonary arteries represents a flow-related phenomenon associated with an increased IVC contribution to the right side of the heart.

MDCT for suspected pulmonary embolism: multi-institutional survey of 16-MDCT data acquisition protocols

The purpose of this study was to determine the extent to which a consensus exists on multidetector row computed tomography (MDCT) protocol parameters for suspected pulmonary embolism (PE). In August of 2004, a questionnaire addressing a number of body MDCT protocols was mailed to 99 fellows of the Society of Computed Body Tomography, representing a total of 46 institutions. In May 2005, this was followed up with a second mailing. The survey requested details pertaining to protocols for the most advanced MDCT scanner in the department. The overall survey response rate of 37% (17/46) yielded 15 protocols for 16-MDCT imaging of suspected PE. This data was tabulated and revealed a consensus for the use of bolus tracking, rapid contrast infusion, caudo-cranial scanning, the narrowest detector row collimation, and thin (<2 mm) reconstruction sections. However, contrast infusion timing, contrast concentration, and implementation of radiation dose modulation were variable. This compilation of protocols reflects recently published studies advocating the use of narrow acquisition collimation and reconstruction sections for MDCT of suspected PE. Future studies are necessary to elucidate the optimal intravenous contrast infusion parameters and further assess the efficacy of reduced radiation dose protocols.

Imaging of Pulmonary Embolism: Self–Assessment Module

The educational objectives for this self-assessment module on imaging of pulmonary embolism are for the participant to exercise, self-assess, and improve his or her understanding of the evaluation of patients with suspected pulmonary embolism using CT angiography; gain familiarity with nonembolic conditions that may be found in patients who are studied with CT angiography for suspected pulmonary embolism; and gain familiarity with the phenomenon of paradoxical embolism, its manifestations on CT angiography, and its radiologic differential diagnosis.

Radiological Reasoning: Pulmonary Embolism—Thinking Beyond the Clots

OBJECTIVE

We discuss the CT findings in a case of pulmonary embolism complicated by paradoxical embolism in a patient with a patent foramen ovale and atrial septal aneurysm.

CONCLUSION

When confronted with a case of pulmonary embolism on CT, besides evaluating the extent of pulmonary artery occlusion, the radiologist should examine the cardiovascular system to identify any unsuspected underlying or associated conditions.

Diagnosis of suspected venous thromboembolic disease in pregnancy

Venous thromboembolic disease is a leading cause of maternal mortality during pregnancy. Early and accurate radiological diagnosis is essential as anticoagulation is not without risk and clinical diagnosis is unreliable. Although the disorder is potentially treatable, unnecessary treatment should be avoided. Most of the diagnostic imaging techniques involve ionizing radiation which exposes both the mother and fetus to finite radiation risks. There is a relative lack of evidence in the literature to guide clinicians and radiologists on the most appropriate method of assessing this group of patients. This article will review the role of imaging of suspected venous thromboembolic disease in pregnant patients, highlight contentious issues such as radiation risk, intravenous contrast use in pregnancy and discuss the published guidelines, as well as suggesting an appropriate imaging algorithm based on the available evidence.

Contrast column interruption artefact in computed tomography pulmonary angiography

Interruption of the contrast column during inspiration can lead to non-diagnostic CT pulmonary angiograms. The importance of this artefact will increase with more CT studies being performed for pulmonary embolism on multidetector row CT. We describe here an instance of such an artefact and discuss its aetiology.

Remnants of Fetal Circulation: Appearance on MDCT in Adults

OBJECTIVE

The objective of our study was to describe the appearance of the remnants of the fetal circulation in adults on MDCT.

CONCLUSION

The use of MDCT allows frequent visualization of the remnants of the umbilical vein, ductus venosus, foramen ovale, ductus arteriosus, and umbilical arteries.

Vascular Diseases of the Thorax: Evaluation with Multidetector CT

The list of vascular diseases in the thorax has been narrowed to three, which are considered essential information for radiologists interpreting CT scans of the thorax: (1) aortic dissection and its variants, intramural hematoma and penetrating atherosclerotic ulcer; (2) acute pulmonary embolism; and (3) coronary artery disease. The spatial resolution of multidetector CT is such that CT has become the imaging modality of choice for aortic dissection and pulmonary embolism. This move away from angiography has transpired over the last decade; perhaps the next decade will see the same occur for evaluation of coronary artery disease.

[Imaging pulmonary embolism]

The diagnostic performance of computed tomography images of pulmonary embolism is directly related to the acquisition parameters. Any physician evaluating these scans must have proper knowledge of the acquisition, injection, reconstruction, and radiation parameters. Cardiac gating and morphological and functional image processing should be understood since they are now routine techniques particularly important for preoperative assessment of chronic thromboembolism. Elementary knowledge of the imaging techniques reduces the risk of diagnostic limitations. Understanding these techniques does not require any particularly advanced knowledge of physics, data processing or technology, but is necessary to chose the appropriate technical facilities and equipment adapted for diagnostic purposes. While specific training is not a prerequisite, interpretation of an angioscan of the pulmonary vessels does require precise knowledge of the pulmonary anatomy in addition to the technical knowledge mentioned above. Proper analysis may reach the 4th and 5th generation vessels. Different analysis methods have been developed which take into account the technical parameters and avoid the need for serial images. Each slice can then be analyzed within an acquisition Volume. Differential diagnosis is also very technique-dependent, minimally operator-dependent but highly machine-dependent. Differential diagnosis becomes less and less a problem with advancing equipment. Sufficient knowledge of the physiological and pathogenic basis is relatively easy to retain.

Multidetector pulmonary CT angiography: advances in the evaluation of pulmonary arterial diseases

Multidetector CT (MDCT) has a primary role in the evaluation of pulmonary artery diseases. Contrast-enhanced MDCT studies are ideally suited for assessment of pulmonary arterial hypertension (PAH) and pulmonary thromboembolic disease. It has become the primary modality to diagnose acute and chronic thromboembolic disease. Its role in the evaluation of pulmonary hypertension is evolving, allowing the radiologist to assess the presence of disease and differentiating intrinsic versus extrinsic pulmonary arterial pathology. An understanding of pulmonary CT angiography, its appropriate application, associated pitfalls, contrast dynamics, and thin-section CT pulmonary and cardiac anatomy is necessary for accurate interpretation by the radiologist. In addition to assessing the pulmonary arteries MDCT has the implicit advantage of thin-section lung parenchymal imaging, a feature that often renders an alternative diagnosis when symptoms of pulmonary arterial disease occur.

Contrast Dynamics During CT Pulmonary Angiogram

OBJECTIVE

Several artifacts have been observed during contrast-enhanced CT of the pulmonary arteries. We describe a physiological artifact caused by a transient interruption of the contrast column in the pulmonary arteries associated with inspiration immediately prior to imaging. This results from a variable inflow of unopacified blood from the inferior vena cava (IVC).

MATERIALS AND METHODS

From 327 consecutive pulmonary CT-angiograms, all performed on a single detector scanner at 3 mm collimation (1.5 mm incremental reconstruction), 50 positive studies, 46 indeterminate studies, and 33 negative studies (129 exams) were retrospectively reviewed by a blinded observer to determine the frequency of the described contrast interruption, its severity (mild, moderate, or severe), and its possible contribution to misinterpretation of studies. The numerical change in Hounsfield units was assigned within the right ventricular chamber for each examination to correlate with the subjective evaluation of severity. Statistical significance was determined with P = 0.05%.

RESULTS

The artifact was present in 48 (37.2%) of the 129 evaluated studies. It was greater in frequency (50.0%) with the negative studies. The presence was 25% with positive studies and 36.7% with indeterminate exams. The interruption was more often mild (<100 HU change) in severity (45.8%). Three (6.6%) definite false positives were detected where the misinterpretation was directly attributed to the artifact. Three (6.6%) other examinations called positive were also directly related to the interrupted contrast column. However, since no further pulmonary vascular evaluation was performed, these examinations can only be considered indeterminate. Two of the latter 3 studies demonstrated a severe (>150 HU change) and the other study demonstrated a moderate (100-150 HU) interruption of contrast opacification.

CONCLUSIONS

During inspiration, there is a variable increase in unopacified venous blood from the IVC, briefly diluting the contrast column entering from the SVC. This interruption is common, though usually mild in severity. However, a short severe interruption of vascular opacification can lead to misinterpretation as a pulmonary embolus or contribute to an indeterminate examination.