Computed Tomography Angiography: The Effect of Different Chaser Flow Rates, Volumes, and Fluids on Contrast Enhancement

Efficacy of the spiral flow generating extended tube during paediatric CCTA

INTRODUCTION

To compare the computed tomography (CT) number for paediatric cardiac computed tomography angiography (CCTA) and visualisation score of the three-dimensional (3D) images using the conventional T-shaped extended tube (T-tube) and spiral flow-generating extended tube (spiral-tube) connected between the contrast injector and cannula.

METHODS

In total, 108 patients suspected to have congenital heart disease (CHD) were considered for inclusion. We utilised the T-tube for intravenous contrast and spiral-tube in 54 patients each. Observers individually inspected randomized volume rendering images of the internal thoracic artery, each acquired from the with or without spiral-tube groups, using a four-point scale. We compared the mean CT number of the ascending aorta (AAO) and pulmonary artery (PA), contrast noise ratio (CNR), CT number for the AAO and PA enhancement ratio, and the visualisation scores between the groups.

RESULTS

There were no significant differences in patient characteristics between the with or without spiral-tube groups (p > 0.05). The mean CT number ±standard deviation for the AAO and PA, and the CNR without or with spiral-tube groups were 441.2 ± 89.2 and 489.8 ± 86.1 HU for the AAO, 436.3 ± 100.6 and 475.3 ± 85.2 HU for the PA, and 9.5 ± 2.2 and 10.8 ± 2.4 for the CNR, respectively (p < 0.05). In the spiral-tube group, the CT number, CNR, and visualisations score of the 3D images were significantly higher for the AAO and PA than those in the T-tube group (p < 0.05).

CONCLUSION

The spiral-tube proved to be beneficial in improving the CT number for the AAO and PA, CNR, and visualisation score compared with the conventional T-tube during paediatric CCTA.

IMPLICATIONS FOR PRACTICE

The spiral-tube may allow the visualisation of smaller blood vessels than those visualised by the conventional T-tube for paediatric patients in CCTA.

Usefulness of a saline chaser to reduce contrast material dose in abdominal CT of normal dogs

Use of a saline chaser has been reported to allow reduction of contrast dose and artifacts during computed tomography (CT) examination in humans. This study assesses the extent of contrast dose by using a saline chaser in abdominal CT scans of normal dogs. Five beagles underwent abdominal CT scans. Three protocols were applied: 600 mg I/kg iohexol without saline chaser (protocol 1), 30% lower dose of iohexol (420 mg I/kg) followed by a 10 mL saline chaser (protocol 2), and 40% lower dose of iohexol (360 mg I/kg) followed by a 10 mL saline chaser (protocol 3). Attenuation values were obtained from aorta, portal vein, and liver parenchyma. The maximum enhancement values (MEVs) in protocol 2 were significantly higher than those in protocols 1 and 3 in the aorta; no difference was seen in the portal vein in all protocols. The liver parenchymal MEVs in protocols 1 and 2 were significantly higher than those obtained in protocol 3. In this study, the use of a saline chaser and a reduced dose of contrast material did not affect vessel enhancement. In conclusion, use of a saline chaser for abdominal CT of dogs is recommended because it allows a 30% reduction of contrast dose without decreasing vascular and hepatic parenchymal enhancement.

Effects of airway pressure on contrast enhancement and diameter of the pulmonary artery in healthy dogs as determined by use of computed tomography angiography

OBJECTIVE

To evaluate effects of airway pressure on contrast enhancement and diameter of the pulmonary artery and determine the optimal airway pressure for pulmonary CT angiography in dogs.

ANIMALS

8 healthy Beagles.

PROCEDURES

Thoracic CT was performed at end-expiration (0 cm H₂O) and 2 positive-pressure end-inspirations (10 and 20 cm H₂O). Attenuation curves of enhancement for the sinus of the pulmonary trunk artery were obtained by use of a bolus technique. Contrast medium (300 mg of I/kg) was administered IV, and CT imaging began at the time of peak enhancement. At each pressure, time to peak enhancement, ratio of blood flow from the caudal vena cava to the right side of the heart (K_CdVC), and enhancement characteristics and diameter changes of the pulmonary artery were evaluated.

RESULTS

All dogs had a significant delay for time to peak enhancement in the sinus of the pulmonary trunk artery as airway pressure increased. The K_CdVC progressively increased as airway pressure increased, and there was low contrast enhancement and increased pulmonary artery filling defects at 20 cm H₂O. All pulmonary arteries had marked increases in diameter as pressure increased. Arterial distensibility in the gravity-dependent cranial lung region was greater than that in the gravity-independent caudal lung region at the 2 positive-pressure end-inspirations.

CONCLUSIONS AND CLINICAL RELEVANCE

Airway pressure affected time to peak enhancement, K_CdVC, contrast enhancement, and pulmonary artery diameter. Results suggested that 10 cm H₂O could be an optimal pressure for evaluation of the pulmonary artery of dogs by use of CT angiography. (Am J Vet Res 2019;80;756-763).

Spiral flow-generating tube for saline chaser improves aortic enhancement in Gd-EOB-DTPA-enhanced hepatic MRI

OBJECTIVES

To evaluate the effect of a spiral tube on contrast enhancement in the hepatic arterial phase (HAP) of gadoxetic acid (Gd-EOB-DTPA)-enhanced magnetic resonance imaging (MRI).

METHODS

In this retrospective study, we observed 104 patients who underwent dynamic MRI of the liver between October 2017 and December 2017. Three Gd-EOB-DTPA injection protocols were compared: (A) conventional method (undiluted Gd-EOB-DTPA, injection rate 1 ml/s, n = 36); (B) spiral dilution method (1:1 diluted Gd-EOB-DTPA with saline [off-label], injection rate 2 ml/s via spiral tube, n = 38); (C) spiral-flushed method (undiluted Gd-EOB-DTPA, injection rate 1 ml/s via spiral tube, n = 30). We regarded protocol-A as a control. The signal-to-noise ratio (SNR) of the abdominal aorta was calculated using arterial phase images. Image contrast and artefacts were evaluated by two board-certified radiologists, using a four-point scale. Statistical analyses included Dunnett's test, the Kruskal-Wallis test and the Steel test.

RESULTS

The SNR of the aorta was significantly higher with protocol-C (25.4 ± 8.8) than protocol-A (20.8 ± 5.4, p = 0.01). There was no significant difference in SNR between protocols A and B (p = 0.47). The contrast score of protocol-C was significantly higher than that of protocol-A (p = 0.0019). There was no significant difference in contrast score between protocols A and B (p = 0.50). There was no significant difference in artefacts among the three protocols (p = 0.96).

CONCLUSIONS

Use of a spiral tube with a slow injection protocol contributed to improved aortic contrast enhancement in the HAP of GD-EOB-DTPA-enhanced hepatic MRI.

KEY POINTS

• Gadoxetic acid shows weaker arterial enhancement at recommended doses, compared with nonspecific gadolinium agents; selection of an appropriate injection protocol is important. • A spiral flow-generating tube improves the transport efficiency of the contrast media, and increases the signal-to-noise ratio of the aorta in hepatic arterial phase. • A spiral flow-generating tube does not contribute to artefact reduction in hepatic arterial phase.

Revival of monophasic contrast injection protocols: superiority of a monophasic injection protocol compared to a biphasic injection protocol in high-pitch CT angiography

BACKGROUND

Biphasic injection protocols are frequently used because they yield homogenous contrast enhancement. We hypothesize that with faster scanners and shorter scan times, biphasic injection protocols are no longer necessary.

PURPOSE

To evaluate whether a monophasic injection protocol is equivalent to a biphasic protocol in terms of contrast enhancement and homogeneity.

MATERIAL AND METHODS

Repeated high-pitch CTA (pitch 3) and conventional standard-pitch computed tomography angiography (CTA) (pitch 1.2) from the cervical region to the symphysis was performed in seven beagles (11.2 ± 2.5 kg) in a cross-over study design. Arterial contrast enhancement was measured along the z-axis in the ascending, descending, and abdominal aorta and the iliac arteries. The z-axis is the longitudinal axis of the human body and at the same time the direction in which the CT table is moving. The data were analyzed using repeated measures ANOVA with a post-hoc t-test and visual assessment of the scans.

RESULTS

In high-pitch CTA, monophasic injection protocols were superior to biphasic injection protocols in enhancement levels (P < 0.05) and enhancement homogeneity along the z-axis (P < 0.05). In conventional CTA, enhancement levels did not differ. Contrast homogeneity was better for biphasic protocols.

CONCLUSION

High-pitch CTA monophasic injection protocols are superior to biphasic injection protocols, due to a higher and more homogeneous contrast enhancement with the same amount of contrast medium used.

Different intravenous contrast media concentrations do not affect clinical assessment of 18F-fluorodeoxyglucose positron emission tomography/computed tomography scans in an intraindividual comparison

OBJECTIVE

The purpose of this study was to perform an intraindividual comparison of the influences of different iodine contrast media on tracer uptake, contrast enhancement, and image quality in combined positron emission tomography (PET)/computed tomography (CT).

MATERIALS AND METHODS

Fifty-one patients underwent baseline and follow-up combined PET/CT consisting of low-dose unenhanced and venous contrast-enhanced CT with contrast media containing a high concentration of iodine (iopromide, 370 mg/mL) and a standard iodine concentration (iopromide, 300 mg/mL). The total iodine load (44.4 g) and the iodine delivery rate (1.29 g/s) were identical for the 2 protocols. The mean and maximum standard uptake values, as measures of tracer uptake and contrast enhancement for unenhanced and contrast-enhanced PET/CT, were quantified at 10 different anatomical sites, and images were analyzed for clinically relevant differences.

RESULTS

The mean and maximum standard uptake values were significantly increased in contrast-enhanced PET/CT compared with unenhanced PET/CT at each anatomical site (P < 0.05). Comparison of tracer uptake between the 300- and 370-mg iodine contrast media showed no significant differences (all P > 0.05). Comparison of contrast enhancement between the 300- and 370-mg iodine contrast media showed no significant difference at any anatomical site (all P > 0.05). Analysis of image quality revealed no clinically relevant differences between the 2 different iodine contrast media (P = 0.739).

CONCLUSION

The use of contrast-enhanced CT scans for attenuation correction in PET/CT does not cause clinically relevant artifacts in PET scan reconstruction, regardless of the iodine concentration used. Standard- and high-iodine contrast media can be used equivalently.

Study on the microbial safety of an infusion set for contrast-enhanced imaging

OBJECTIVES

Multiple uses of automatic contrast injection systems may impose septic risks on patients. The purpose of this experiment was to verify whether a newly developed replaceable patient-delivery system may allow multiple uses of the system but without such risks.

METHODS

Twelve patient-delivery systems were tested according to a multiple-use approach using an automatic contrast injection system consisting of dual syringes and one filling and injecting set. Two protocols with normal saline only (n = 6) or contrast media plus normal saline (n = 6) loaded in the injection system were performed. Each patient-delivery system was connected through an infusion catheter to the ear vein of a rabbit that was intravenously preinjected with a diffusible radiotracer (99m)Tc-dimercaptopropionyl-human serum albumin. Aliquots were sampled from the filling and injecting set, patient line, and animal blood for radioactive analysis after the replacement of each patient-delivery system.

RESULTS

For the protocol performed using only normal saline, radioactivity was found in the blood circulation of the rabbit (1655903 ± 593221 CPM) and in the patient line (52894 ± 33080 CPM), but, virtually, in none of samples from the filling and injecting set (8 ± 3 CPM), relative to the background (7 ± 3 CPM) (P = 0.726). Similarly, experimental results attained using contrast plus saline show radioactivity in the blood circulation of the rabbit (1119107 ± 183174 CPM) as well as in the patient line (32991 ± 20232 CPM) but in none of samples from the filling and injecting set (6 ± 6 CPM), relative to the background (6 ± 4 CPM) (P = 0.955).

CONCLUSIONS

The tested patient-delivery system proves convenient and safe. It allows multiple uses of the contrast injection system and avoids the risk of cross contamination.

Porcine ex vivo liver phantom for dynamic contrast-enhanced computed tomography: development and initial results

OBJECTIVES

: To demonstrate the feasibility of developing a fixed, dual-input, biologic liver phantom for dynamic contrast-enhanced computed tomography (CT) imaging and to report initial results of use of the phantom for quantitative CT perfusion imaging.

MATERIALS AND METHODS

: Porcine livers were obtained from completed surgical studies and perfused with saline and fixative. The phantom was placed in a body-shaped, CT-compatible acrylic container and connected to a perfusion circuit fitted with a contrast injection port. Flow-controlled contrast-enhanced imaging experiments were performed using 128-slice and 64-slice dual-source multidetector CT scanners. CT angiography protocols were used to obtain portal venous and hepatic arterial vascular enhancement, reproduced over a period of 4 to 6 months. CT perfusion protocols were used at different input flow rates to correlate input flow with calculated tissue perfusion, to test reproducibility, and to determine the feasibility of simultaneous dual-input liver perfusion. Histologic analysis of the liver phantom was also performed.

RESULTS

: CT angiogram 3-dimensional reconstructions demonstrated homogenous tertiary and quaternary branching of the portal venous system to the periphery of all lobes of the liver as well as enhancement of the hepatic arterial system to all lobes of the liver and gallbladder throughout the study period. For perfusion CT, the correlation between the calculated mean tissue perfusion in a volume of interest and input pump flow rate was excellent (R = 0.996) and color blood flow maps demonstrated variations in regional perfusion in a narrow range. Repeat perfusion CT experiments demonstrated reproducible time-attenuation curves, and dual-input perfusion CT experiments demonstrated that simultaneous dual input liver perfusion is feasible. Histologic analysis demonstrated that the hepatic microvasculature and architecture appeared intact and well preserved at the completion of 4 to 6 months of laboratory experiments and contrast-enhanced imaging.

CONCLUSIONS

: We have demonstrated successful development of a porcine liver phantom using a flow-controlled extracorporeal perfusion circuit. This phantom exhibited reproducible dynamic contrast-enhanced CT of the hepatic arterial and portal venous system over a 4- to 6-month period.