Exponentially Decelerated Contrast Media Injection Rate Combined With a Novel Patient-Specific Contrast Formula Reduces Contrast Volume Administration and Radiation Dose During Computed Tomography Pulmonary Angiography:

Development and Evaluation of a CT Pulmonary Angiography Protocol Dedicated to Pregnant and Postpartum Women

INTRODUCTION

This study presents and evaluates a CT pulmonary angiography protocol dedicated to pregnant women. The specific feature of this protocol is to place the region of interest (ROI) (bolus detection) in the superior vena cava. The objective is to evaluate the performances of this method.

MATERIALS AND METHODS

The protocol uses a iodine-based contrast agent at 300mgI/mL and an injection rate of 5 to 6 mL/sec for an injection volume of 50 mL of iodine contrast agent followed by 40 mL of NaCl. The ROI is positioned on the superior vena cava, with a 100 Hounsfield units (HU) threshold, and the acquisition is performed at 100 kVp. This protocol was evaluated retrospectively on a large population (n = 105: group 1) and compared with a control group that did not benefit from this protocol (n = 55: group 2). Both groups were studied on the same device in the same center. Each examination was evaluated and classified into 3 groups: optimal, suboptimal, and noncontributory. Dose length products (DLP) values were also recorded. Statistical tests were applied to the data collected.

RESULTS

The rate of noncontributory examinations increased from 43.1% for the control group to 4.8% for the new protocol group. The reference enhancement level in the pulmonary trunk is 250 UH. The mean enhancement in the pulmonary trunk of the new protocol group (332 HU (±71 HU (±71 HU)) is significantly greater than the reference value of 250 HU (P < .0001), which is not the case for control group (P = .3485 > .05), which has a mean enhancement of 239 HU (±87 HU). The control group had a mean DLP of 225 mGy.cm (±81 mGy.cm), and the new-protocol group had a mean DLP of 189 mGy.cm (±75 mGy.cm).

DISCUSSION

Our noncontributory examination rate is the lowest rate described in the literature. Our protocol contradicts standard practices of placing an ROI in the pulmonary trunk for bolus detection of iodinated contrast media.

CONCLUSION

The results of this study showed that this protocol reduces the number of noncontributory examinations while reducing the dose delivered to patients. This robust protocol is applicable to other devices and meets perfectly radiation-safety requirements and injected contrast media volume limitation.

Impact of various iodine concentrations of iohexol and iodixanol contrast media on image reconstruction techniques in a vascular-specific contrast media phantom: quantitative and qualitative image quality assessment

PURPOSE

The aim of our study is to investigate the impact of iodine quantification on image reconstruction when employing a vascular-specific contrast media phantom with varying iodine concentrations.

MATERIALS AND METHODS

A 30-cm phantom simulating arterial and venous blood vessel diameters was manufactured. Small (9 mm) and medium (12 mm) cylinders contained iodine concentrations from 10 to 100% while large (21 mm) cylinders were in quartiles from 25 to 100% diluted in blood equivalent medium. Each phantom was filled with either iohexol 350 mgI/mL (Group A) or iodixanol 320 mgI/mL (Group B) and then scanned separately. For each group, tube potential (80-140 kVp) and current (50-400 mAs) were changed and all image series were reconstructed with filtered back projection (FBP), hybrid-based iterative reconstruction (HBIR) and model-based iterative reconstruction (MBIR). Mean opacification was measured in all groups. All data were compared employing an independent t test and Pearson's correlation. Visual grading characteristic (VGC) and Cohens' kappa analyses were performed.

RESULTS

At 80 kVp, mean opacification using HBIR was significantly higher in Group B (2165 ± 1108 HU) than in Group A (2040 ± 1036 HU) (p < 0.009). At 140 kVp, MBIR and HBIR were greater in Group A (1704 ± 1033 HU and 1685 ± 1023 HU) versus Group B (1567 ± 1036 HU and 1567 ± 1034 HU) (p < 0.022). CNR using FBP, HBIR and MBIR was higher in Group B (46 ± 42 HU, 70 ± 163 HU and 83 ± 74 HU, respectively) than in Group A (43 ± 39 HU, 174 ± 130 HU and 80 ± 65 HU, respectively) (p < 0.0001-0.035). Qualitative image analysis demonstrated no difference in Cohen's kappa analysis. VGC was higher in Group A at all image reconstruction groups.

CONCLUSION

Iohexol outperforms iodixanol in observer performance when assessing image reconstruction techniques and iodine concentrations in a vascular-specific contrast media phantom.

Ultra-low dose contrast CT pulmonary angiography in oncology patients using a high-pitch helical dual-source technology

PURPOSE

We aimed to determine if the image quality and vascular enhancement are preserved in computed tomography pulmonary angiography (CTPA) studies performed with ultra-low contrast and optimized radiation dose using high-pitch helical mode of a second generation dual source scanner.

METHODS

We retrospectively evaluated oncology patients who had CTPA on a 128-slice dual-source scanner, with a high-pitch helical mode (3.0), following injection of 30 mL of Ioversal at 4 mL/s with body mass index (BMI) dependent tube potential (80-120 kVp) and current (130-150 mAs). Attenuation, noise, and signal-to-noise ratio (SNR) were measured in multiple pulmonary arteries. Three independent readers graded the images on a 5-point Likert scale for central vascular enhancement (CVE), peripheral vascular enhancement (PVE), and overall quality.

RESULTS

There were 50 males and 101 females in our study. BMI ranged from 13 to 38 kg/m2 (22.8±4.4 kg/m2). Pulmonary embolism was present in 29 patients (18.9%). Contrast enhancement and SNR were excellent in all the pulmonary arteries (395.3±131.1 and 18.3±5.7, respectively). Image quality was considered excellent by all the readers, with average reader scores near the highest possible score of 5.0 (CVE, 4.83±0.48; PVE, 4.68±0.65; noise/quality, 4.78±0.47). The average radiation dose length product (DLP) was 161±60 mGy.cm.

CONCLUSION

Using a helical high-pitch acquisition technique, CTPA images of excellent diagnostic quality, including visualization of peripheral segmental/sub-segmental branches can be obtained using an ultra-low dose of iodinated contrast and low radiation dose.

An augmented patient-specific approach to administration of contrast agent for CT renal angiography

Purpose

This hybrid retrospective and prospective study performed on 200 consecutive patients undergoing renal CTA, investigates the opacification of renal vasculature, radiation dose, and reader confidence.

Materials and Methods

100 patients were assigned retrospectively to protocol A and the other 100 were allocated prospectively to protocol B. Both protocols implemented a contrast material and saline flow rate of 4.5 mL/sec. Protocol A utilized a 100 mL of low-osmolar nonionic IV contrast material (Ioversol 350 mg I/mL) while protocol B employed a patient-tailored contrast media formula using iso-osmolar non-ionic (Iodixanol 320 mg I/mL).

Results

Arterial opacification in the abdominal aorta and in the bilateral main proximal renal arteries demonstrated no statistical significance (p>0.05). Only the main distal renal artery of the left kidney in protocol B was statistically significant (p<0.046). In the venous circulation, the IVC demonstrated a significant reduction in opacification in protocol B (59.39 HU ± 19.39) compared to A (87.74 HU ± 34.06) (p<0.001). Mean CNR for protocol A (22.68 HU ± 13.72) was significantly higher than that of protocol B (14.75 HU ± 5.76 p< 0.0001). Effective dose was significantly reduced in protocol B (2.46 ± 0.74 mSv) compared to A (3.07 ± 0.68 mSv) (p<0.001). Mean contrast media volume was reduced in protocol B (44.56 ± 14.32 mL) with lower iodine concentration. ROC analysis demonstrated significantly higher area under the ROC curve for protocol B (p< 0.0001), with inter-reader agreement increasing from moderate to excellent in renal arterial visualization.

Conclusion

Employing a patient-tailored contrast media injection protocol shows a significant refinement in the visualization of renal vasculature and reader confidence during renal CTA.

Split-bolus contrast injection protocol enhances the visualization of the thoracic vasculature and reduced radiation dose during chest CT

OBJECTIVE

To investigate the visualization of mediastinal lymph nodes during thoracic CT employing a multiphasic contrast media (CM) protocol.

METHODS

Institutional review board approved retrospective study consisting of 300 patients with known chest malignancy. Patients were allocated to one of two CM protocols: Protocol A, consisted of dual bolus (Phase 1:100 ml CM followed by 100 ml saline chaser) i.v. injected at 2.5 ml s^-1; Protocol B employed 100 ml of CM using a multiphasic injection protocol (Phase 1 and 2:60 ml contrast and saline, followed by Phase 3 and 4:40 ml contrast and saline injected at 2.5 ml s^-1) with a fixed scan delay of 70 s for each acquisition. Attenuation profiles of the thoracic arteries and veins were calculated as well as the arterio-venous contrast ratios (AVCR). Receiver operating characteristic (ROC), visual grading characteristic (VGC), and Cohen's kappa analysis were assessed.

RESULTS

Arterial opacification was up to 24% (p < 0.032) higher in protocol B than A, whereas, in the veins it was significantly lower in protocol B than A, with a maximum reduction of up to 84% (p < 0.0001). There was no statistical significance between the central and peripheral pulmonary arteries [>263 Hounsfield units (HU)] in each protocol. Protocol B, demonstrated significant improvement in AVCR at various anatomical sites (p < 0.002). Radiation dose was significantly reduced in protocol B compared to A (p < 0.004). Both ROC and VGC demonstrated significantly higher Az score for protocol B compared to A (p < 0.0001) with an increased inter reader agreement from poor to excellent.

CONCLUSION

Employing a multiphasic CM protocol significantly improves opacification of the thoracic vasculature and visualization of mediastinal lymph nodes during thoracic CT.

ADVANCES IN KNOWLEDGE

Uniform opacification between thoracic arteries and veins increases the delineation between vasculature and lymph nodes, reduces radiation dose when employing a multiphase contrast media injection protocol.

Imaging of acute pulmonary embolism: an update

Imaging plays an important role in the evaluation and management of acute pulmonary embolism (PE). Computed tomography (CT) pulmonary angiography (CTPA) is the current standard of care and provides accurate diagnosis with rapid turnaround time. CT also provides information on other potential causes of acute chest pain. With dual-energy CT, lung perfusion abnormalities can also be detected and quantified. Chest radiograph has limited utility, occasionally showing findings of PE or infarction, but is useful in evaluating other potential causes of chest pain. Ventilation-perfusion (VQ) scan demonstrates ventilation-perfusion mismatches in these patients, with several classification schemes, typically ranging from normal to high. Magnetic resonance imaging (MRI) also provides accurate diagnosis, but is available in only specialized centers and requires higher levels of expertise. Catheter pulmonary angiography is no longer used for diagnosis and is used only for interventional management. Echocardiography is used for risk stratification of these patients. In this article, we review the role of imaging in the evaluation of acute PE.

State-of-the-Art Pulmonary CT Angiography for Acute Pulmonary Embolism

OBJECTIVE

Pulmonary CT angiography (CTA) is the imaging modality of choice in suspected acute pulmonary embolism (PE). Current pulmonary CTA techniques involve ever lower doses of contrast medium and radiation along with advanced postprocessing applications to enhance image quality, diagnostic accuracy, and provide added value in patient management. The objective of this article is to summarize these current developments and discuss the appropriate use of state-of-the-art pulmonary CTA.

CONCLUSION

Pulmonary CTA is well established as a fast and reliable means of excluding or diagnosing PE. Continued developments in CT system hardware and postprocessing techniques will allow incremental reductions in radiation and contrast material requirements while improving image quality. Advances in risk stratification and prognostication from pulmonary CTA examinations should further refine its clinical value while minimizing the potential harm from overutilization and overdiagnosis.