Imaging Findings of Peripheral Arterial Disease on Lower-Extremity CT Angiography Using a Virtual Monoenergetic Imaging Algorithm

Abstract

Peripheral arterial disease (PAD) is common in elderly patients. Lower-extremity CT angiography (LE-CTA) can be useful for detecting PAD and planning its treatment. PAD can also be accurately evaluated on reconstructed monoenergetic images (MEIs) from low kiloelectron volt (keV) to high keV images using dual-energy CT. Low keV images generally provide higher contrast than high keV images but also feature more severe image noise. The noise-reduced virtual MEI reconstruction algorithm, called the Mono+ technique, was recently introduced to overcome such image noise. Therefore, this pictorial review aimed to present the imaging findings of PAD on LE-CTA and compare low and high keV images with those subjected to the Mono+ technique. We found that, in many cases, the overall and segmental image qualities were better and metal artifacts and venous contamination were decreased in the high keV images.

Keywords: Computed Tomography, X-Ray; Lower Extremity; Peripheral Arterial Disease.

Fig. 1. Example of dual-energy CT protocol for lower-extremity CT angiography using SOMAOM FLASH or SOMATOM Force, Siemens Healthineers.

Fig. 2. Monoenergetic image plus technique.

Fig. 3. Lower-extremity CT angiography images using the MEI plus technique of a 75-year-old male with peripheral arterial disease (body mass index, 22.9 kg/m²; CT volume dose index, 8.45 mGy; and dose-length product, 1157 mGy·cm).

A-F. The MEIs (window level, 45 HU; window width, 450 HU) include (A) 40 keV, (B) 50 keV, (C) 60 keV, (D) 70 keV, and (E) 80 keV. An occlusion was noted in the left tibioperoneal trunk, proximal posterior tibial artery, and bilateral anterior tibial arteries (not shown). The overall image quality is adequate and good with beam hardening artifacts (white arrows) on the 40 and 50 keV MEIs, respectively (A, B). The beam hardening artifacts close to the right profunda femoris artery (black arrows) can affect the vessel evaluation by radiologists. However, the overall image quality is excellent with little beam hardening in the 60–80 keV MEIs (C-E). Poly-energetic (80/140 kVp with a tin filter) image appears similar to the 120 kVp image and the high keV images (F). HU = Hounsfield units, MEI = monoenergetic image

Fig. 4. Lower-extremity CT angiography images using the MEI plus technique of a 57-year-old male with peripheral arterial disease (body mass index, 25.4 kg/m²; CT volume dose index, 8.66 mGy; dose-length product, 1266 mGy·cm).

A-F. The MEIs shown include (A) 40 keV, (B) 50 keV, (C) 60 keV, (D) 70 keV, and (E) 80 keV. An occlusion was noted in the right internal iliac artery (not shown). The overall image quality is poor with severe streak artifacts (arrows) on the 40 keV MEI (A). The overall image quality is superior on the 70–80 keV (D, E) MEIs to the low keV MEIs (A-C). Poly-energetic (80/140 kVp with a tin filter) image appears similar to the 120 kVp image and the high keV images (F). MEI = monoenergetic image

Fig. 5. Lower-extremity CT angiography image using the MEI plus technique of a 63-year-old male with diabetes mellitus macroangiopathy and a below-the-left-knee amputation (body mass index, 21.2 kg/m²; CT volume dose index, 7.74 mGy; dose-length product, 978 mGy·cm).

A-F. The MEIs (window level, 45 HU; window width, 450 HU) shown include (A) 40 keV, (B) 50 keV, (C) 60 keV, (D) 70 keV, and (E) 80 keV. Venous contamination is visible (arrows) and compromised diagnostic interpretation at just above the knee level of the left leg on the 40–50 keV images (A, B). Although venous contamination is visible in the 60 keV image, it did not affect the diagnostic interpretation (D). Minimal venous contamination is visible in the 70–80 keV images (D, E). Poly-energetic (80/140 kVp with a tin filter) image shows similar to the 120 kVp image and the high keV images (F). HU = Hounsfield units, MEI = monoenergetic image

Fig. 6. Lower-extremity CT angiography images using the MEI plus technique of an 86-year-old male with diffuse steno-occlusive disease in the bilateral BTK arteries (body mass index, 15.1 kg/m²; CT volume dose index, 7.09 mGy; dose-length product, 911 mGy·cm).

A-E. The MEIs (window level, 45 HU; window width, 450 HU) shown include (A) 40 keV, (B) 50 keV, (C) 60 keV, (D) 70 keV, and (E) 80 keV. Venous contamination is visible (arrows) that compromises the diagnostic interpretation at the BTK arteries of the left leg in the 40–50 keV images (A, B). Although venous contamination is visible on the 60–80 keV images, it did not affect diagnostic interpretation (C-E). BTK = below-the-knee, HU = Hounsfield units, MEI = monoenergetic image

Fig. 7. Lower-extremity CT angiography images using the MEI plus technique of a 37-year-old male with left diabetes mellitus foot (body mass index, 26.5 kg/m²; CT volume dose index, 8.57 mGy; dose-length product, 1236 mGy·cm).

A-E. MEIs (window level, 45 HU; window width, 450 HU) shown include (A) 40 keV, (B) 50 keV, (C) 60 keV, (D) 70 keV, and (E) 80 keV. Venous contamination is visible (arrows) and compromised diagnostic interpretation in the left lower leg arteries in the 40–50 keV images (A, B). Although venous contamination is visible in the 60–80 keV images, it did not affect the diagnostic interpretation (C-E). HU = Hounsfield units, MEI = monoenergetic image

Fig. 8. Lower-extremity CT angiography images using the MEI plus technique in a 79-year-old male (body mass index, 17.3 kg/m²; CT volume dose index, 7.20 mGy; dose-length product, 947 mGy·cm) with peripheral arterial disease. Severe stenosis was noted at the bilateral superficial femoral arteries (arrowheads).

A-E. MEIs (window level, 500 HU; window width, 2000 HU) shown include (A) 40 keV, (B) 50 keV, (C) 60 keV, (D) 70 keV, and (E) 80 keV. At 40 keV, the segmented image provides acceptable information but the image quality is unsatisfactory due to vessel calcification with mild blooming artifacts (arrowheads). At 50–60 keV, the segmented images satisfactorily provide information with adequate image quality. However, at 70–80 keV, the segmented images provide optimal information with excellent image quality and no blooming artifacts. The image quality of peripheral arterial disease with calcification on the higher keV images is superior to that on the lower keV images. HU = Hounsfield unit, MEI = monoenergetic image

Fig. 9. Lower-extremity CT angiography images using the MEI plus technique of an 82-year-old female (body mass index, 40.7 kg/m²; CT volume dose index, 8.88 mGy; dose-length product, 1104 mGy·cm) with peripheral arterial disease. Severe stenosis is noted at the right superficial femoral artery (arrowheads).

A-E. MEIs (window level, 150 HU; window width, 600 HU) shown include (A) 40 keV, (B) 50 keV, (C) 60 keV, (D) 70 keV, and (E) 80 keV. At 40–50 keV, the segmented images provide acceptable information but the image quality is unsatisfactory due to vessel calcification with blooming artifacts (arrowheads) At 60 keV, the segmented images satisfactorily provide information with adequate image quality. However, at 70–80 keV, the segmented images provide optimal information with excellent image quality. F-J. The MEIs with modification in the window setting (window level, 500 HU; window width, 2000 HU) shown include (F) 40 keV, (G) 50 keV, (H) 60 keV, (I) 70 keV, and (J) 80 keV. At 40–80 keV, the segmented images provide acceptable to optimal information of the evaluation of vessel calcification without blooming artifacts. HU = Hounsfield units, MEI = monoenergetic image

Fig. 10. Lower-extremity CT angiography images using the MEI plus technique in a 90-year-old female (body mass index, 21.9 kg/m²; CT volume dose index, 7.1 mGy; dose-length product, 936 mGy·cm) with peripheral arterial disease at the bilateral superficial femoral arteries, popliteal arteries, and below-the-knee arteries. Moderate stenosis is noted in the left popliteal artery (arrowhead).

A-E. MEIs (WL: 500 HU, WW: 2000 HU) shown include (A) 40 keV, (B) 50 keV, (C) 60 keV, (D) 70 keV, and (E) 80 keV. At 40 keV (arrowhead), the segmented image of the left popliteal artery provides unclear information with inadequate image quality due to severe blooming artifacts. However, at 50–80 keV, the segmented images provide optimal information with adequate to excellent image quality and a decrease in blooming artifacts compared with the 40 keV image. F-J. The MEIs shown include (F) 40 keV, (G) 50 keV, (H) 60 keV, (I) 70 keV, and (J) 80 keV with changes in window setting. In each keV image, the WL and WW were adjusted to optimize image quality (A) WL: 1040 HU, WW: 4200 HU, (B) WL: 800 HU, WW: 3400 HU, (C) WL: 500 HU, WW: 2100 HU, (D) WL: 600 HU, WW: 2200 HU, (E) WL: 530 HU, WW: 2000 HU). With the WW and WL adjustments, the image quality improved at all keV, even 40 keV, with a decrease in blooming artifacts, showing excellent image quality. HU = Hounsfield units, MEI = monoenergetic image, WL = window level, WW = window width

Fig. 11. Lower-extremity CT angiography images using the MEI plus technique of a 69-year-old female (body mass index, 23.4 kg/m²; CT volume dose index, 7.16 mGy; dose-length product, 830 mGy·cm) with peripheral arterial disease. Mild stenosis is noted at the left superficial femoral artery (arrowheads).

A-E. The MEIs (window level, 45 HU; window width, 450 HU) shown include (A) 40 keV, (B) 50 keV, (C) 60 keV, (D) 70 keV, and (E) 80 keV. At 40–50 keV, the segmented images provide acceptable information but unsatisfactory image quality due to vessel calcification with blooming artifacts (arrowheads). At 60–80 keV, the segmented images provide satisfactory information with adequate image quality such that the vessel calcification is differentiated from the vessel enhancement. F-J. The MEIs with modified window settings (window level, 600 HU; window width, 2000 HU) shown include (F) 40 keV, (G) 50 keV, (H) 60 keV, (I) 70 keV, and (J) 80 keV. Thus, at 40–80 keV, the segmented images provide acceptable to optimal information of the evaluation of vessel calcification without blooming artifacts. HU = Hounsfield units, MEI = monoenergetic image

Fig. 12. Lower-extremity CT angiography images using the MEI plus technique in a 60-year-old female (body mass index, 24.2 kg/m²; CT volume dose index, 7.78 mGy; dose-length product, 990 mGy·cm) with peripheral arterial disease.

A-E. MEIs shown include (A) 40 keV, (B) 50 keV, (C) 60 keV, (D) 70 keV, and (E) 80 keV. Metal artifacts caused by internal fixation material on the left femur affected the left superficial femoral artery evaluation. At 40–50 keV, the image quality is poor and non-diagnostic due to strong streak artifacts (arrows). In the 60–80 keV images, the image quality is poor due to severe artifacts, but the effect of the artifacts gradually decreases in the images from 40 to 80 keV. F-J. The MEIs shown include (F) 40 keV, (G) 50 keV, (H) 60 keV, (I) 70 keV, and (J) 80 keV with optimized window settings (window level, 1000 HU; window width, 3000 HU) due to a decrease in metal artifacts. Despite the window setting changes, the low keV images (F, G) show remnant metal artifacts compared with the high keV images (H-J). HU = Hounsfield units, MEI = monoenergetic image

Fig. 13. Lower-extremity CT angiography images using the MEI plus technique of a 61-year-old male (body mass index, 18.5 kg/m²; CT volume dose index, 7.54 mGy; dose-length product, 939 mGy·cm) with peripheral arterial disease.

A-E. MEIs shown include (A) 40 keV, (B) 50 keV, (C) 60 keV, (D) 70 keV, and (E) 80 keV. Metal artifacts caused by the internal fixation material on the left femur and tibia affect the left popliteal artery evaluation. In the 40–50 keV images, the image quality is poor due to severe artifacts (arrows). In the 60–80 keV images, the image quality is adequate with slight metal artifacts. The metal artifacts gradually decrease in the images from 40 to 80 keV. F-J. MEIs shown include (F) 40 keV, (G) 50 keV, (H) 60 keV, (I) 70 keV, and (J) 80 keV with optimized window settings (window level, 700 HU; window width, 3000 HU) due to the decrease in metal artifacts. With the window level and width adjustments, the vessel image quality is excellent without metal artifacts. HU = Hounsfield units, MEI = monoenergetic image

Fig. 14. Lower-extremity CT angiography images using the MEI plus technique of a 79-year-old female (body mass index, 24.0 kg/m²; CT volume dose index, 7.28 mGy; dose-length product, 803 mGy·cm) with peripheral arterial disease.

A-E. MEIs shown include (A) 40 keV, (B) 50 keV, (C) 60 keV, (D) 70 keV, and (E) 80 keV. Metal artifacts caused by internal fixation material on the left femur affect the left superficial femoral artery evaluation. In the 40–50 keV images, the image quality is poor due to severe artifacts (arrows). In the 60–80 keV images, the image quality is adequate with slight metal artifacts. The metal artifacts gradually decrease in the images from 40 to 80 keV. F-J. MEIs shown include (F) 40 keV, (G) 50 keV, (H) 60 keV, (I) 70 keV, and (J) 80 keV with optimized window settings (window level, 200 HU; window width, 2000 HU) due to the decrease in metal artifacts. With the window level and width adjustments, the vessel image quality is excellent without metal artifacts. HU = Hounsfield units, MEI = monoenergetic image