Evaluation of the Abdominal Aorta and External Iliac Arteries Using Three-Dimensional Time-of-Flight, Three Dimensional Electrocardiograph-Gated Fast Spin-Echo, and Contrast-Enhanced Magnetic Resonance Angiography in Clinically Healthy Cats

Abstract

Arterial thromboembolism is associated with high morbidity and mortality rates in cats. Definitive diagnosis requires advanced imaging modalities, such as computed tomography angiography (CTA) and contrast-enhanced (CE) magnetic resonance angiography (MRA). However, CTA involves exposure to a large amount of ionized radiation, and CE-MRA can cause systemic nephrogenic fibrosis. Non-contrast-enhanced (NE) MRA can help accurately diagnose vascular lesions without such limitations. In this study, we evaluated the ability of NE-MRA using three-dimensional electrocardiograph-gated fast spin-echo (3D ECG-FSE) and 3D time-of-flight (3D TOF) imaging to visualize the aorta and external iliac arteries in clinically healthy cats and compared the results with those obtained using CE-MRA. All 11 cats underwent 3D ECG-FSE, 3D TOF, and CE-MRA sequences. Relative signal intensity (rSI) for quantitative image analysis and image quality scores (IQS) for qualitative image analysis were assessed; the rSI values based on the 3D TOF evaluations were significantly lower than those obtained using 3D ECG-FSE (aorta 3D TOF: 0.57 ± 0.06, aorta 3D ECG-FSE: 0.83 ± 0.06, P < 0.001; external iliac arteries 3D TOF: 0.45 ± 0.06, external iliac arteries 3D ECG-FSE:0.80 ± 0.05, P < 0.001) and similar to those obtained using CE-MRA (aorta: 0.58 ± 0.05, external iliac arteries: 0.57 ± 0.03). Moreover, IQS obtained using 3D TOF were significantly higher than those obtained using 3D ECG-FSE (aorta 3D TOF: 3.95 ± 0.15, aorta 3D ECG-FSE: 2.32 ± 0.60, P < 0.001; external iliac arteries 3D ECG-FSE: 3.98 ± 0.08, external iliac arteries 3D ECG-FSE: 2.23 ± 0.56, P < 0.001) and similar to those obtained using CE-MRA (aorta: 3.61 ± 0.41, external iliac arteries: 3.57 ± 0.41). Thus, 3D TOF is more suitable and produces consistent image quality for visualizing the aorta and external iliac arteries in clinically healthy cats and this will be of great help in the diagnosis of FATE.

Keywords: abdominal aorta; arterial thromboembolism; external iliac arteries; feline; magnetic resonance angiography (MRA).

Figure 1

An eight-channel human knee coil with a 1.5-T magnet was used for signal reception. Under inhalational anesthesia, the cat was placed in the sternal recumbency position with the hind limbs caudally extended; the thigh region was included in the coil. To prevent the hind limbs from being disturbed, the sponge and hind limbs were fixed together and blankets and hot packs were applied over the cat to maintain its body temperature. MRI, magnetic resonance imaging.

Figure 2

Maximum-intensity projection reconstruction of non-contrast-enhanced 3D TOF magnetic resonance angiography images of the dorsal view (A) and lateral view (C), and contrast-enhanced 3D TOF fast spoiled gradient-echo magnetic resonance angiography images of the dorsal view (B) and lateral view (D) of the feline aorta and external iliac arteries at 1.5 Tesla. The solid arrow indicates the aorta, and the open arrows indicate the external iliac arteries. 3D TOF, three-dimensional time-of-flight.

Figure 3

Dorsal single-shot fast spin-echo (SSFSE) images for cat 6 (A) and cat 8 (B). Single-shot two-dimensional acquisition, which is a prerequisite for performing 3D ECG-FSE, was not achieved because a clean peripheral pulse gating waveform could not be obtained due to the fast heart rate of cat 6. However, single-shot 2D acquisition was normally achieved for cat 8. The 3D ECG-FSE images of D and F are compared in Figure 5. 3D ECG-FSE, three-dimensional echocardiograph-gated fast spin echo magnetic resonance angiography; SSFSE, single-shot fast spin-echo.

Figure 4

Box and whisker plots of rSI for the aorta and external iliac arteries measured using 3D ECG-FSE, 3D TOF and CE-MRA for clinically healthy cats. Boxes indicate the sample variation, and whiskers represent the standard deviation. It was confirmed that the rSI of 3D ECG-FSE was significantly higher than that of 3D TOF and CE-MRA for all arterial segments. Although the rSI of 3D TOF was lower than that of CE-MRA for aorta and external iliac arteries, however there was no significant difference. ****Statistically significant difference (P < 0.001) determined by an analysis of variance followed by the one-way ANOVA. rSI, relative signal intensity; 3D ECG-FSE, three-dimensional echocardiograph-gated fast spin echo; 3D TOF, three-dimensional time-of-flight; FSPGR, contrast-enhanced 3D TOF fast spoiled gradient-echo; ns, no significance.

Figure 5

Maximum-intensity projection reconstruction of magnetic resonance angiography images of each dorsal and oblique views obtained using 3D TOF (A–C), 3D ECG-FSE (D–F) and FSPGR. The aorta and external iliac arteries were excellently delineated with no venous contamination and were scored as “Excellent” (A,B,G). In (C,D,H), it was scored as “Good” due to minor venous contamination. Considering the margin of the arterial wall, the venous contamination overlapping the aorta and external iliac arteries, and the overall diagnostic qualities, image reconstruction was scored as “Fair” (E), and “poor” (F), respectively. N/A, not available; 3D ECG-FSE, three-dimensional echocardiograph-gated fast spin echo; 3D TOF, three-dimensional time-of-flight; FSPGR, contrast-enhanced 3D TOF fast spoiled gradient-echo.

Figure 6

Cat 7. The aorta and external iliac arteries were not the same during the first [(A), left] and second [(A), right] trial using 3D ECG-FSE. Moderate-to-severe venous contamination is observed [(A), arrow], and intermittent filling defect-like artifacts are observed in the aorta [(A), arrowhead]. A visible difference in the diameters (A) of the vessels in the aorta and the caudal vena cava was observed [(A), left and right, empty arrow]. The first trial and second trial resulted in observations similar with those obtained using 3D TOF (B). 3D ECG-FSE, three-dimensional echocardiograph-gated fast spin-echo magnetic resonance angiography; 3D TOF, three-dimensional time-of-flight; MRA, magnetic resonance angiography.