Current contrast media delivery strategies for cardiac and pulmonary multidetector-row computed tomography angiography

Optimizing low contrast volume thoracic CT angiography: From the basics to the advanced

Contrast-enhanced CT angiography (CTA) is a widely used, noninvasive imaging technique for evaluating cardiovascular structures. Contrast-induced nephrotoxicity is a concern in renal disease; however, the true nephrotoxic potential of iodinated contrast media (CM) is unknown. If a renal impaired patient requires CTA, it is important to protect the kidneys from further harm by reducing total iodinated CM volume while still obtaining diagnostic quality imaging. These same reduced volume CM techniques can also be applied to nonrenal impaired patients in times of CM shortage. This educational review discusses several modifications to CTA that can be adapted to both conventional 64-slice and the newer generation CT scanners which enable subsecond acquisition with a reduced CM volume technique. Such modifications include hardware and software adjustments and changes to both the volume and flow rate of administered CM, with the goal to reduce the dose of CM without compromising diagnostic yield.

Update for the Performance of CT Coronary Angiography

BACKGROUND

 Coronary CT angiography (cCTA) is a class 1 recommendation in the current guidelines by the European Society of Cardiology (ESC) for excluding significant coronary artery stenosis. To achieve optimal image quality at a low radiation dose, the imaging physician may choose different acquisition modes. Therefore, the consensus guidelines by the Society of Cardiovascular Computed Tomography (SCCT) provide helpful guidance for this procedure.

METHOD

 The article provides practical recommendations for the application and acquisition of cCTA based on the current literature and our own experience.

RESULTS AND CONCLUSION

 According to current ESC guidelines, cCTA is recommended in symptomatic patients with a low or intermediate clinical likelihood for coronary artery disease. We recommend premedication with beta blockers and nitrates prior to CT acquisition under certain conditions even with the latest CT scanner generations. The most current CT scanners offer three possible scan modes for cCTA acquisition. Heart rate is the main factor for selecting the scan mode. Other factors may be coronary calcifications and body mass index (BMI).

KEY POINTS

  · CCTA is a valid method to exclude coronary artery disease in patients with a low to intermediate clinical likelihood.. · Even with the latest generation CT scanners, premedication with beta blockers and nitrates can improve image quality at low radiation exposure.. · Current CT scanners usually provide retrospective ECG gating and prospective ECG triggering. Dual-source scanners additionally provide a "high pitch" scan mode to scan the whole heart during one heartbeat, which may also be achieved using single-source scanners with broad detectors in some cases.. · Besides the available scanner technology, the choice of scan mode primarily depends on heart rate and heart rate variability (e. g., arrhythmia)..

CITATION FORMAT

· Soschynski M, Hagar MT, Taron J et al. Update for the Performance of CT Coronary Angiography. Fortschr Röntgenstr 2022; DOI: 10.1055/a-1747-3554.

Pulmonary arteries: imaging of pulmonary embolism and beyond

The pulmonary arteries are not just affected by thrombus. Various acquired and congenital conditions can also affect the pulmonary arteries. In this review we discuss cross sectional imaging modalities utilized for the imaging of the pulmonary arteries. Acquired pulmonary artery entities, including pulmonary artery sarcoma (PAS), vasculitis, aneurysm, and arteriovenous malformations, and congenital anomalies in adults, including proximal interruption of the pulmonary artery, pulmonary sling, pulmonary artery stenosis, and idiopathic dilatation of the pulmonary trunk, are also discussed. An awareness of these entities and their imaging findings is important for radiologists interpreting chest imaging.

Effect of bolus tracking region-of-interest position within the descending aorta on luminal enhancement of coronary arteries in coronary computed tomography angiography

To compare coronary artery luminal enhancement in coronary computed tomography angiography (CCTA) between ventral and dorsal region-of-interest (ROI) bolus tracking in the descending aorta.The records of 165 consecutive patients who underwent CCTA with non-helical acquisition from July 2017 to March 2018 were retrospectively examined. We performed 320-row CCTA with bolus tracking [scan triggered at 260 HU in the descending aorta] and 133 patients were finally included. ROI was set in the ventral and dorsal halves of the descending aorta in 68 and 65 patients, respectively.Contrast arrival time was significantly shorter in the dorsal group (ventral: 21.8 ± 0.372 s; dorsal: 20.7 ± 0.369; P = .0295). The mean density of the proximal and distal RCA was significantly higher in the ventral group (proximal: ventral, 428.1 ± 6.95 HU; dorsal, 405.5 ± 7.72 HU, P = .0318; distal: ventral, 418.0 ± 9.29 HU; dorsal, 393.2 ± 9.46 HU, P = .0133).Dorsal bolus tracking ROI in the descending thoracic aorta significantly reduced preparation time and RCA CT values.

Coronary angiography using second-generation dual source computed tomography: Feasibility of low dose and low flow rate to achieve appropriate individual contrast enhancement using a test bolus-based contrast medium protocol-A CONSORT compliant article

Improved contrast enhancement consistency can be achieved using an individualized contrast media (CM) protocol. This study aimed to assess the feasibility of a low-dose, low-flow rate CM protocol to achieve appropriate individual contrast enhancement using a newly advocated individualized test bolus-based protocol for second-generation dual-source computed tomography angiography.CM containing iodine (370 mg I/mL) was used in this study. A CM flow rate of 3.5 mL/s for patients with a body mass index (BMI) <25.0 kg/m, and 4.5 mL/s for those with BMI ≥25.0 kg/m was used in group 1 (n = 189). An individualized test-bolus based contrast injection protocol was then derived from the information gained from the test bolus and coronary enhancements in group 1. The proposed individualized test-bolus based CM injection protocol was applied in group 2 (n = 219). Ascending aortic attenuations (AAo) were measured and compared with both groups.The contrast enhancement consistency of AAo in group 2 improved significantly (31.8 vs 56.3 Hounsfield units [HU]; P < .001). The number of patients in group 2 with a contrast flow rate ≤3 mL/s was 63 (28.8%), with 77 (35.2%) using a contrast dose ≤40 mL. In group 2, no significant differences in mean AAo were found among subgroups with contrast flow rates ≤3.0, 3.1 to 4.0, 4.1 to 5.0 and >5.0 mL/s (351, 344, 346, and 348 HU, respectively), nor among subgroups with contrast doses ≤40, 41 to 50, 51 to 60, and >60 mL (349, 345, 344, and 350 HU, respectively).Improved individual contrast enhancement uniformity can be achieved using an individualized CM protocol tailored to a test bolus. Approximately, one-third of patients received CM at a flow rate of no more than 3 mL/s and a total dose of no more than 40 mL.

Subjective and objective image differences in pediatric computed tomography cardiac angiography using lower iodine concentration

BACKGROUND

Several recent studies showed the optimal contrast enhancement with a low-concentration and iso-osmolar contrast media in both adult and pediatric patients. However, low contrast media concentrations are not routinely used due to concerns of suboptimal enhancement of cardiac structures and small vessels.

OBJECTIVE

To evaluate the feasibility of using iso-osmolar contrast media containing a low iodine dose for CT cardiac angiography at 80 kilovolts (kVp) in neonates and infants.

MATERIALS AND METHODS

The iodixanol 270 group consisted of 79 CT scans and the iopromide 370 group of 62 CT scans in patients ≤1 year old. Objective measurement of the contrast enhancement was analyzed and contrast-to-noise ratios of the ascending aorta and left ventricle were calculated. Regarding subjective measurement, a four-point scale system was devised to evaluate degrees of contrast enhancement, image noise, motion artifact and overall image quality of each image set. Reader performance for correctly differentiating iodixanol 270 and iopromide 370 by visual assessment was evaluated.

RESULTS

Group objective and subjective measurements were nonsignificantly different. Overall sensitivity, specificity and diagnostic accuracy for correctly differentiating iodixanol 270 and iopromide 370 by visual assessment were 42.8%, 59%, and 50%, respectively.

CONCLUSION

The application of iodixanol 270 achieved optimal enhancement for performing pediatric cardiac CT angiography at 80 kVp in neonates and infants. Objective measurements of contrast enhancement and subjective image quality assessments were not statistically different in the iodixanol 270 and iopromide 370 groups.

The influence of cardiac function on coronary arterial enhancement at coronary computed tomography angiography: A cross-sectional study

Background:

The purpose of this study was to evaluate the influence of ejection fraction (EF) on peak aortic time (PAT) and peak aortic enhancement (PAE) during coronary computed tomography angiography (CTA).

Materials and Methods:

One-hundred and twenty patients (64 men, 56 women) underwent measurement of coronary CTA with a measurement of EF within 3 months of coronary CTA. Pearson's correlation coefficient analysis was used to investigate the relationships between EF, PAT and PAE, and peak attenuation of all coronary arteries.

Results:

The range of EF was (25%–70%) (mean: 55 ± 7.7). The range of PAT and PAE of ascending aorta on bolus test was 13–31 s (mean: 19.3 ± 2) and 153–435 HU (mean: 235 ± 40.6), respectively. Mean peak attenuation of ascending aorta, right coronary artery, left coronary artery, left circumflex artery, and left anterior descending were (561 ± 119), (476 ± 109), (505 ± 108), (467 ± 113), and (473 ± 104), respectively. There was a negative correlation between EF and PAT (r = −0.266, P = 0.003); however, there was no significant correlation between EF and PAE (r = −0.027, P = 0.767). In addition, there was no significant correlation between EF and the peak attenuation of coronary arteries.

Conclusion:

PAT was related to EF, but there was no relationship between PAE and EF. One of the explanation is that the left ventricular EF used for our study was assessed with echocardiography which is used roughly estimation of EF with interval of 5%–10% and may cause confounding results.

Contrast Circulation Time to Assess Right Ventricular Dysfunction in Pulmonary Embolism: A Retrospective Pilot Study

Objective

To optimize enhancement of pulmonary arteries and facilitate diagnosis of pulmonary embolism (PE), modern computed tomography angiography (CTA) contains a contrast bolus tracking system. We explored the diagnostic accuracy of the time-intensity curves given by this automated system to identify right ventricular dysfunction (RVD) in acute PE.

Methods

114 CTAs with a diagnosis of PE were reviewed. RVD was defined as right-to-left ventricular diameter ratio of 1 or greater. Four parameters on time-intensity curves were identified. Parameters between CTAs with and those without RVD were compared with the Wilcoxon rank-sum test. The ability of the four parameters to discriminate patients with RVD was explored by compiling the area under the operating curves (AUC).

Results

The time needed by the contrast media to reach the pulmonary artery [8 seconds (IQR: 7–9) versus 7 seconds (IQR: 6–8), p<0.01], the time needed to reach 40 Hounsfield units (HU) [11 seconds (IQR: 8.5–14) versus 9.5 seconds (IQR: 8–10.5), p<0.01], and the contrast intensity reached after 10 seconds [19 HU (IQR: 4–67) versus 53 HU (IQR: 32–80), p<0.05] were all statistically different between CTA with and CTA without RVD. Those three parameters changed gradually across severity categories of RVD (p<0.05 for trend). Their AUC to identify RVD ranged from 0.63 to 0.66. The slope of contrast intensity over time was not informative: [31 HU/s (IQR: 20–57) in CTA with, compared to 36 HU/s (IQR: 22.5–53) in CTA without RVD, p = 0.60].

Conclusion

Several parameters of the time-intensity curve obtained by the bolus tracking system are associated with RVD assessed on CTA images. Of those, the time needed to reach a predefined threshold seems to be the easiest to obtain in any CTA without additional processing time or contrast injection. However, the performance of those parameters is globally low.

Looking beyond the thrombus: essentials of pulmonary artery imaging on CT

Background

Pulmonary arteries are not just affected by thrombus. Congenital and acquired conditions can also involve the pulmonary arteries. An awareness of these conditions is important for the radiologist interpreting chest computed tomography (CT).

Methods

The anatomy of the pulmonary arteries was reviewed. CT and magnetic resonance (MR) acquisition protocols for imaging the pulmonary arteries were discussed. The imaging appearances of congenital and acquired anomalies involving the pulmonary arteries, using CT and other modalities, were presented.

Results

Imaging features of congenital anomalies presented include pulmonary agenesis, partial pulmonary artery agenesis, patent ductus arteriosus, pulmonary artery sling, congenital pulmonary artery stenosis and coronary to pulmonary artery fistula. Acquired pulmonary artery anomalies discussed include arteritis, infected aneurysm and sarcoma. Pulmonary artery filling defects besides thromboembolism are also discussed, including foreign body emboli. Imaging features of bronchogenic carcinoma and mediastinal fibrosis demonstrating compression of the pulmonary arteries are presented, followed by a brief discussion of post repair appearance of the pulmonary arteries for congenital heart disease.

Conclusions

Congenital and acquired pulmonary artery anomalies have a characteristic appearance on a variety of imaging modalities. An acquaintance with the imaging features of these anomalies is needed to avoid misinterpretation and reach the correct diagnosis.

Teaching Points

• Discuss a variety of congenital and acquired anomalies of the pulmonary arteries.

• Discuss the imaging appearance of the presented congenital or acquired pulmonary artery anomalies.

• Describe CT and MR acquisition protocols for imaging the pulmonary arteries.

• Review the anatomy of the pulmonary arteries.

Challenges to protocol optimization due to unexpected variation of CT contrast dose amount and flow

High-quality computed tomography (CT) exams are critical to maximizing radiologist's interpretive ability. Exam quality in part depends on proper contrast administration. We examined injector data from consecutive abdominal and pelvic CT exams to analyze variation in contrast administration. Discrepancies between intended IV contrast dose and flow rate with the actual administered contrast dose and measured flow rate were common. In particular, delivered contrast dose discrepancies of at least 10% occurred in 13% of exams while discrepancies in flow rate of at least 10% occurred in 42% of exams. Injector logs are useful for assessing and tracking this type of variability which may confound contrast administration optimization and standardization efforts.