Dual-energy CT angiography in suspected pulmonary embolism: influence of injection protocols on image quality and perfused blood volume

Abstract

To compare intravenous contrast material (CM) injection protocols for dual-energy CT pulmonary angiography (CTPA) in patients with suspected acute pulmonary embolism with regard to image quality and pulmonary perfused blood volume (PBV) values. A total of 198 studies performed with four CM injection protocols varying in CM volume and iodine delivery rates (IDR) were retrospectively included: (A) 60 ml at 5 ml/s (IDR = 1.75gI/s), (B) 50 ml at 5 ml/s (IDR = 1.75gI/s), (C) 50 ml at 4 ml/s (IDR = 1.40gI/s), (D) 40 ml at 3 ml/s (IDR = 1.05gI/s). Image quality and PBV values at different resolution settings were compared. Pulmonary arterial tract attenuation was highest for protocol A (397 ± 110 HU; p vs. B = 0.13; vs. C = 0.02; vs. D < 0.001). CTPA image quality of protocol A was rated superior compared to protocols B and D by reader 1 (p = 0.01; < 0.001), and superior to protocols B, C and D by reader 2 (p < 0.001; 0.02; < 0.001). Otherwise, there were no significant differences in CTPA quality ratings. Subjective iodine map ratings did not vary significantly between protocols A, B, and C. Both readers rated protocol D inferior to all other protocols (p < 0.05). PBV values did not vary significantly between protocols A and B at resolution settings of 1, 4 and 10 (p = 0.10; 0.10; 0.09), while otherwise PBV values displayed a decreasing trend from protocol A to D (p < 0.05). Higher CM volume and IDR are associated with superior CTPA and iodine map quality and higher absolute PBV values.

Photon-counting CT for diagnosis of acute pulmonary embolism: potential for contrast medium and radiation dose reduction

“…Before each scan, a predefined amount of iodinated contrast medium was applied (Imeron® 350, Bracco) via an antecubital vein using an automated injector. In the EID group, 50 mL of contrast medium was administered with a flow rate of 4 mL/s, corresponding to an iodine delivery rate of 1400 mg/s [ 14 , 15 ]. Based on recent studies discussing a potential for contrast medium dose savings in PCD-CT by up to 50% while still obtaining diagnostic attenuation [ 13 , 16 ], we aimed for a significant reduction in terms of halving the dose of our standard dual-energy acquisition protocol.…”

Dual-Energy CT in Cardiothoracic Imaging: Current Developments

“…Owing to improvements in detector sensitivity and the enhanced spectral separation of newer DECT scanners, it is also possible to scan without injecting a saline chaser. Injection rates of 40 mL and below with 3 mL/s were considered insufficient for good-quality iodine maps, whereas a higher amount of contrast medium was associated with a higher quality of iodine maps [ 38 ]. Bacon et al reported a total volume of up to 100 mL (300 mg iodine/mL) [ 39 ].…”

“…Bacon et al reported a total volume of up to 100 mL (300 mg iodine/mL) [ 39 ]. In the literature, the delay varies from 7 to 12–15 s [ 38 , 40 , 41 ], and triggering thresholds are recommended to be 100–120 HU [ 38 , 39 ]. Considering the inter-individual differences between the patients and scanning hardware, these protocols should be an orientation for creating an ideal protocol for each site and radiographer using their experience.…”

“…Pulmonary artery contrast can also be negatively affected by patients contracting abdominal muscles while holding their breath for the examination, thus performing a vasovagal maneuver leading to the contrast agent being pressed retrogradely from the right heart into the superior vena cava. Kosmala et al described insufficient contrast of the pulmonary arteries in some patients even though the bolus timing was estimated correctly [ 38 ]. Furthermore, detecting smaller segmental areas of hypoperfusion and embolisms can sometimes be difficult, especially for residents and trainees [ 4 , 22 , 43 ].…”

Diagnosis of acute heart failure in CT pulmonary angiography: feasibility and accuracy

“…Computed tomography pulmonary angiography (CTPA), owing to its high sensitivity and specificity as well as wide availability, represents the imaging modality of choice for the diagnosis or exclusion of pulmonary embolism [ 5 , 11 , 12 ]. The scan initiation of CTPA is usually performed with the bolus tracking technique which enables an individualized optimization of the scan start in relation to the contrast arrival in the pulmonary artery circulation [ 13 , 14 ]. Still, there are numerous factors affecting the timing of contrast enhancement in CTPA which are not being taken into account entirely with bolus tracking.…”