Available online at http://www.biij.org/2010/1/e10 doi: 10.2349/biij.6.1.e10 biij Biomedical Imaging and Intervention Journal CASE REPORT Multislice CT angiography of the plantar arch L Field, Z Sun*, BSc, PhD Department of Imaging and Applied Physics, Curtin University of Technology, Perth, Australia Received 21 August 2009; received in revised form 29 October 2009, accepted 1 November 2009 ABSTRACT The aim of this case report is to present a multislice computed tomography angiography (CTA) procedure for viewing the plantar arch. A CTA was requested to determine the vascular sufficiency of the plantar arch of a 64-year- old patient with necrotic and gangrenous toes. The patient had recently undergone a proximal wedge osteotomy procedure for correction of a hallux valgus deformity. A 16-detector row CT scanner with 1.25 mm slice thickness and 0.625 mm reconstruction interval was used to reconstruct multiplanar reformats, maximum intensity projections and three-dimensional volume rendered images of the foot in question in both arterial and venous phases to determine if pathology of the plantar arch was present. The 3D reconstructed images of CTA demonstrated a loss of continuity of the plantar arch between the first and third metatarsals. This case report shows the diagnostic value of multislice CTA, especially 3D visualisation in the assessment of peripheral vascular branches. © 2010 Biomedical Imaging and Intervention Journal. All rights reserved. Keywords: plantar arch, computed tomography angiography, 3D visualisation, hallux valgus, peripheral arteries INTRODUCTION cells and tissues as a consequence of reduced blood flow to that area. Traditionally, peripheral angiography is Hallux valgus is a common joint deformity performed to investigate the main arteries of the lower involving the first metatarsophalangeal joint resulting in limb and their branches; however, it is not only an a change in the cosmetic appearance of the foot and invasive procedure but also associated with abnormal presentations such as pain and discomfort, complications. With the advent of multislice computed depending on the degree of abnormality [1-3]. Blood tomography (MSCT), especially the 16- and 64-slice CT, supply to the lower extremity is extremely important, large anatomic coverage can be easily achieved in a short especially in patients with hallux valgus as the peripheral time with high resolution images [4, 5]. artery branches could be involved. The small plantar arch Submillimetre CT scanning allows acquisition of artery is very clinically significant in this abnormality nearly isotropic volume data with 16-slice CT because the necrotic toes are an indication of the death of (0.5×0.5×0.6 mm) and isotropic volume data with 64-slice CT (0.4×0.4×0.4 mm) [5, 6]. Thus, anatomic details such as peripheral blood vessels can be clearly demonstrated with MSCT angiography. In addition to the * Corresponding author. Present address: Discipline of Medical Imaging, Department of Imaging and Applied Physics, Curtin 2D axial images, high-resolution volume data permits University of Technology, GPO Box, U1987, Perth, Western Australia generation of a series of 2D and 3D reconstruction 6845, Australia. Tel: +61-8-9266 7509; Fax: +61-8-9266 4344; images to enhance diagnostic value of MSCT for E-mail: [email protected] (Zhonghua Sun). L Field et al. Biomed Imaging Interv J 2010; 6(1):e10 2 This page number is not for citation purposes (a) (b) Figure 1 MPR view of the right plantar arch. Sagittal MPR images (A, B) demonstrate the plantar arch with apparent artifacts arising from the metal k- wires. assessment of both normal vascular branches and IMAGING GENERATION AND VISUALIZATION abnormal changes [7, 8]. Of these reconstructions, multiplanar reformation (MPR), maximum-intensity The imaging examination was performed on a projection (MIP) and volume rendering (VR) are most 16-detector row CT scanner (GE Lightspeed CT, commonly used in clinical practice. GE Healthcare, Milwaukee, WI, USA) with the scanning In this case report, the authors present an interesting protocol as follows: 120 kVp, 200-250 mAs, beam patient with hallux valgus with necrotising toes. MSCT collimation 16 x 0.625 mm, gantry rotation time 500 ms, angiography images in 2D and 3D reconstructions were section thickness of 1.25 mm, pitch 1.375 and generated to demonstrate the diagnostic value of these reconstruction interval of 0.625 mm. The area of scan images in the assessment of vascular supply to the coverage ranged from the lower third of tibia to the feet. peripheral arteries. During the procedure, 100 mL of a contrast medium (Isovue 370) was infused with 50 mL of saline and injected via a double power injector into the patient’s PATIENT HISTORY antecubital vein at a rate of 4 mL/s to visualise the vessels in and around the foot. A bolus tracking A 64-year-old man presented to the radiology technique (Smart prep) of the thoracic abdominal aorta department 8 days post hallux valgus corrective surgery. threshold of 100 HU over baseline was used to ensure Due to the severity of the patient’s hallux valgus maximum enhancement of the peripheral vessels. A scan deformity, the surgery involved a proximal osteotomy of delay of 60-70 seconds was used to demonstrate the the first metatarsal with three k-wires, as well as pins venous supply to the lower extremity. inserted through the second, third and fourth In addition to 2D axial views, a number of 3D metatarsophalangeal joints to maintain the bony reconstructions were generated to demonstrate the alignment of these areas. After the surgery, the second peripheral arteries. These reconstructions included multi- and possibly third toe on the patient’s right foot had planar reformation (MPR), maximum-intensity become necrotic and gangrenous. The medical team was projection (MIP) and three-dimensional volume rendered querying the possibility of insufficiency of the plantar (3D VR) reconstructions of the foot. These particular arch of the right foot, and requested an MRI to be reconstructions were used to effectively answer the performed on this foot. After examining the request form, clinical question and allow the plantar arch to be viewed a radiologist determined that a CTA procedure for the as clearly as possible. Arterial and venous phase images plantar arch would be more advisable in this situation were also produced to determine if the problem was due due to the large amount of orthopaedic hardware present to arterial or venous insufficiency. in the foot, but that an MRI would also be helpful to Figure 1 is a sagittal MPR view of the plantar arch, view the soft tissue areas of the foot after the CTA while Figure 2 is a series of MIP images showing the examination was performed. disruption of the plantar arch artery along its distal segment based on coronal and sagittal views. L Field et al. Biomed Imaging Interv J 2010; 6(1):e10 3 This page number is not for citation purposes (a) (b) (c) (d) (e) L Field et al. Biomed Imaging Interv J 2010; 6(1):e10 4 This page number is not for citation purposes (f) (g) (h) Figure 2 MIP visualisation of the plantar arch arteries. Coronal (A-D) and sagittal (E-H) MIP images show that the distal plantar arteries are occluded due to necrosis and occlusion in the location between 1st and 3rd metatarsal bones. L Field et al. Biomed Imaging Interv J 2010; 6(1):e10 5 This page number is not for citation purposes (a) (b) (c) (d) (e) Figure 3 3D VR of the plantar arch arteries. VR images demonstrate the bony components and peripheral artery branches in the right foot (A-C), and the artery branches only (D, E). The distal plantar arteries between 1st and 3rd metatarsal bones are occluded. L Field et al. Biomed Imaging Interv J 2010; 6(1):e10 6 This page number is not for citation purposes 3D VR images shade and colour pixels depending lower limb with the aim of assessing the presence of on their level of attenuation [9]. The VR reconstruction thrombus and atherosclerotic formations within the reveals surface and internal features, and allows the 3D arteries branching directly from the iliac arteries [13]. images to be rotated in real time [10]. Figure 3 However, the application of this technique in viewing the demonstrates 3D VR images of the vascular supply plantar arch is limited in the literature. Due to the through the area of interest with and without bony invasiveness of conventional angiography, MSCT has components. become widely used in clinical practice as an effective All of the above images demonstrate a loss of alternative to invasive angiography for visualisation of continuity of the plantar arch between the first and third vascular disease [15], including the peripheral artery metatarsal. The presence of the k-wires can also be seen branches, as shown in this case report. by the metallic artifacts present on the images, While 2D axial CT images are routinely used in particularly along the first metatarsal (Figs 2D, 3D). clinical practice, some kind of 2D or 3D reconstructions are required to provide information which is not available with 2D axial views, but still necessary for DISCUSSION AND CONCLUSION clinical requirements. MPR is the most commonly used complementary visualisation to 2D axial images as it Hallux valgus is a bony deformity that affects the allows quick demonstration of the relationship between first metatarsophalangeal joint. It involves a valgus anatomical structures. However, a number of MPR movement of the proximal phalanx of the first metatarsal images are required to demonstrate the entire course of with an associated varus drift of the metatarsal head arteries and their branches, since not all of the vascular which can cause bursitis over the medial eminence of the segments can be displayed in a single MPR view. This first metatarsal with associated pain and discomfort [1]. was observed in this case report (Fig 1), thus, application Schweitzer et al [11] reported that the presence of an of MPR views in assessment of distal vascular territory, eminence, commonly referred to as a bunion, is seen in such as plantar arch is limited. 95% of hallux valgus sufferers, while bursitis of the first MIP has been widely recognized as the most useful metatarsal head is experienced in 70% of cases. visualisation tool in CT angiography as it provides Radiographically, hallux valgus is assessed using angiographic-like images less invasively. The principle weight- or load-bearing views of the affected foot, in of MIP images is the demonstration of only maximum order to determine the extent of loss of the transverse CT number encountered in each ray. The differentiation arch of the foot [12]. There is little to no use for between contrast-enhanced blood vessels and multislice CT or MRI in diagnosing this disorder. Dorsi- background is good, thus high-density structures such as plantar (DP), DP oblique and lateral weight-bearing contrast-enhanced vessels and calcification can be radiographs are obtained, and measurements are taken clearly depicted and displayed on MIP images. MIP was off these radiographs to determine the severity of the found very useful in this case as it clearly shows the disorder [3]. These measurements include the angle made main arteries and their peripheral branches (Fig 2). between the first metatarsal and phalanges known as the However, MIP images do not provide depth information hallux valgus angle, and the intermetatarsal angle, or the which is the main drawback for visualisation of complex angle between the first and second metatarsals [11]. The anatomy. main limitation of these measurements is the lack of 3D VR provides a 3D representation of the providing vascular details in patients with suspected anatomical structures based on a volume dataset, since it ischemic or necrotic changes. utilises all of the information contained in the data. A MSCT allows acquisition of images much faster and voxel-based intensity histogram is generated, and several with better quality and resolution than single-slice CT [4, parameters such as colour, brightness and opacity are 5, 13]. These technical improvements have significantly assigned to each voxel according to its CT attenuation advanced the applications of MSCT, especially CT value. Therefore, 3D relationship between different angiography (CTA) procedures. Schoepf et al [13] stated structures can be easily displayed and appreciated on VR, that MSCT allows CTA procedures to be used quickly as shown in Figure 3. VR allows demonstration of both and accurately for diagnosis of suspected vascular vascular branches and bony components in a single diseases in all organ systems. Clinical CTA applications image, thus it significantly enhances understanding of are vast, and include examinations for the aorta, coronary the complex anatomic structures. VR requires extensive arteries, carotid arteries, pulmonary vessels, vessels user interaction for accurate evaluation of complex throughout the abdomen, brain and peripheral arteries [6- anatomical structures. Currently, advanced 3D post- 9, 14]. processing software packages are available in most of the CTA of the peripheral arteries of the lower limb is recent MSCT scanners, so the VR display of these an application that has been significantly enhanced with complex structures including peripheral arteries becomes the development of MSCT technique as longer anatomic feasible without further segmentation. VR image quality coverage is required to be obtained in a single breath- is determined by the resolution of original source data. hold scan. Traditionally, examinations of this area In this case study, radiologists were specifically required the use of invasive angiography to examine the looking for evidence to confirm the lack of presence of run-off of the iliac and femoral arteries throughout the the plantar arch, a relatively small artery located deep L Field et al. Biomed Imaging Interv J 2010; 6(1):e10 7 This page number is not for citation purposes within the foot. While MIP images provide necessary information about the patency of the plantar arch arteries, the use of 3D VR reconstructions through the plantar arch were extremely important to diagnose and confirm that the continuity of the plantar arch had indeed been lost and blood flow to the digits of the foot had been compromised. These reconstructions allowed both internal and surface features to be seen and allowed all images to be rotated in real time. Without using 3D VR reconstructions, determining the sufficiency of the plantar arch in this case would have been almost impossible and the patient’s long-term health and quality of life would have been significantly affected. In conclusion, the authors have demonstrated the application and usefulness of MSCT angiography in the assessment of vascular supplies to the small plantar artery in a patient diagnosed with hallux valgus. 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