High Temporal and Spatial Resolution Imaging of Peripheral Vascular Malformations

VASCULAR MALFORMATIONS ARE defects in the circulatory system generally formed during development. They are present in approximately 1.5% of the population and may lead to pain, pathologic bone fractures, and muscle contractures as a result of invasion into surrounding tissue structures (1). Treatment of vascular malformations is targeted at destruction of the nidus, reduction of potential for growth of the vascular malformation, and prevention of clinical consequences. However, treatment options are relatively limited and may worsen symptoms if not appropriately applied (2). Treatment planning requires accurate characterization of the vascular lesion including: (i) the extent of the vascular malformation (focal, multifocal, or diffuse), (ii) its involvement with surrounding tissue (muscle, bone, nerves, tendons, subcutaneous tissue, and skin), (iii) the feeding and draining vessels, and (iv) the classification of the lesion. Vascular malformations are most commonly classified by flow rate (high flow versus low flow) (3) and type (arterial, venous, capillary, lymphatic, or mixed) (4). Low flow lesions are generally treated with sclerotherapy, which involves direct injection of a sclerosing agent to the nidus of the vascular malformation. Treatment of high flow lesions generally requires a multifaceted approach, and sclerotherapy with flow control by means of embolization is often used as one part of treatment (2). Characterization of vascular malformations is generally done with imaging techniques such as digital subtraction angiography (DSA), ultrasound (US), and more recently, MRI. DSA provides high temporal (≤ 1 s frame time) and high spatial resolution (≤ 1 mm) but is an invasive procedure that uses iodinated contrast material and ionizing radiation with images acquired as projections (5). Ultrasound may be used to image the flow of superficial lesions but lacks tissue penetration, has a small imaging field-of-view, and the exam quality is highly operator dependent. An MRI protocol using T1 and T2-weighted imaging is currently the preferred method as it offers noninvasive imaging with high spatial resolution that is able to characterize the structure of the lesion and its involvement with the surrounding tissue (6–10). MR angiography (MRA) (11–13) may be useful as part of the MR evaluation of vascular malformations (8). In particular, time-resolved contrast-enhanced MR angiography (CE-MRA) techniques (14,15) with both high temporal and spatial resolution may provide structural detail of the malformation and normal vasculature as well as functional information about the feeding and draining vessels and vascular malformation (3,16–18). Time-resolved CE-MRA with short frame times and high spatial resolution has been made possible by the development of parallel acquisition. If applied along the two phase encoding directions of three-dimensional (3D) acquisition (19), parallel acquisition can provide acceleration factors (R) of 6 or higher (20,21). These can be combined with various k-space sampling patterns (15,20,22), often in conjunction with view-sharing (23), to reconstruct image frames at a rate faster than that of the inherent acquisition time. When the acceleration (R) of 2D methods such as SENSE (19) is combined with the acceleration RHD allowed by homodyne reconstruction, the overall net acceleration RNET = R × RHD, can routinely be 10-fold or higher, making it possible to acquire time-resolved contrast-enhanced angiograms of the peripheral vasculature with 1-mm isotropic spatial resolution and ≤ 6-s frame time (24–26). The purpose of this work is to assess the performance of a recently developed highly accelerated (RNET = 14.4) 3D time-resolved CE-MRA technique, Cartesian Acquisition with Projection-Reconstruction-like sampling (CAPR), for accurate characterization and treatment planning of vascular malformations of the periphery.