- CT angiography in complex upper extremity reconstruction.
- Multidetector CT and three-dimensional CT angiography of upper extremity arterial injury
- Extremity Arteriography: Purpose and Procedure
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Spectrum of peripheral vascular trauma : A comprehensive review of imaging features with surgical correlation T. Triveni Yadav. Acute Arterial Thrombosis of the Hand. References Publications referenced by this paper. Upper extremities vasculature. Blunt polytrauma: evaluation with section whole-body CT angiography. David Dreizin , Felipe Munera. Dual-energy D. Coronary artery stent evaluation by combining iterative reconstruction and high-resolution kernel at coronary CT angiography. Dual-energy CT: vascular applications. High origin of an ulnar artery--development and surgical significance.
New iterative reconstruction techniques for cardiovascular computed tomography: how do they work, and what are the advantages and disadvantages? Rendon C. Nelson , Sebastian Feuerlein , Daniel T. Persistent median artery: cadaveric study and review of the literature.
CT angiography in complex upper extremity reconstruction.
Non—contrast-enhanced techniques often overestimate stenoses in the setting of complex vessel anatomy or abnormal blood flow and can be time consuming. CE-MRA is robust and less time consuming. A major challenge for all CE-MRA techniques is to achieve optimal timing of the contrast bolus relative to the sampling of the center of k -space, which is crucial for optimal imaging.
The specific MRA protocol chosen should be tailored to the patient to provide the best possible image quality. A broad spectrum of vascular disorders of the upper extremity, ranging from the thoracic outlet syndrome to distal disease, such as thromboangiitis obliterans and hypothenar hammer syndrome, can be assessed accurately using MRA of the upper extremity. The main requisite for diagnostic MRA is to achieve sufficient spatial resolution and sufficient vessel contrast.
A high-field magnetic resonance MR scanner 1. Dedicated phased-array extremity or wrist coils should be used whenever possible, depending on the region of interest and required coverage. This results in a significant difference in signal intensity between blood and adjacent tissue when using heavily T1-weighted arterial-phase imaging. The image acquisition must be timed with the contrast bolus peak during the sampling of the center of k -space to achieve maximum vessel contrast. Before the contrast material is injected, a nonenhanced acquisition with the same sequence settings as the contrast-enhanced scans can be acquired to allow for subtraction with the subsequent arterial-phase images.
Subtracted images can be further manipulated with a maximum intensity projection MIP visualization to produce 3-D representations of the arterial anatomy. Recent approaches in the lower extremity using Dixon-based methods are an alternative approach that can be used to suppress background fat signal potentially obviating subtraction. The advantages of CE-MRA include short scan times and high spatial resolution with minimal flow-related artifacts. Overall, however, the safety profile of GBCAs is excellent and generally exceeds that of iodinated agents.
Temporal resolution can add clinically valuable information to an examination of the upper extremity, including collateral flow pathways associated with stenoses and visualization of arterial to venous shunting. Another major advantage of time-resolved imaging is that it obviates a timing bolus or real-time fluorotriggering techniques. Most time-resolved MRA techniques use view-sharing methods to achieve high temporal resolution while maintaining high spatial resolution. Such approaches use frequent sampling of low spatial frequencies center of k -space with less frequent sampling of higher spatial frequencies periphery of k -space that are subsequently shared between the final reconstructed 3-D data sets.
These methods are commonly used in combination with subtraction, obtained by acquiring a precontrast mask, ultimately providing a set of time-resolved 3-D data images showing progressive enhancement of vessels akin to DSA. A major advantage is that not only morphologic but also dynamic information is obtained, which may allow for evaluation of the hemodynamic relevance of a stenosis.
From the rapidly acquired multiple images, the best arterial or other relevant phase can be chosen. Time-resolved MRA can be performed in the same imaging session together with high-resolution standard MRA for more detailed depiction of small vessels.
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Newer techniques are ECG-gated balanced steady-state free precession, flow-sensitive dephasing, and arterial spin labeling techniques. Appropriate use of these techniques can allow diagnosis of vascular diseases in patients with chronic kidney disease without using contrast materials. TOF MRA is based on the principle that the protons in blood flowing into a presaturated imaging section of interest are unsaturated and thereby provide fresh magnetization when excited with the radiofrequency pulse.
Furthermore, by placing a saturation band above or below the section of interest, the direction of blood flow can be assessed. Disadvantages of this method include small imaging volumes, long acquisition times, and artifacts related to either slow or turbulent flow. These artifacts can impede assessment of vascular disease, potentially causing false-positive overdetection of vascular stenoses.
PC MRA requires the acquisition of 2 or more typically 4 data sets or flow-compensated pulses to generate flow-sensitive phase images.
Phase data can be used either to reconstruct velocity-encoded flow-quantification images or MRA images. This technique is commonly used for flow imaging and measurement of flow but only in rare cases is it used for pure angiographic imaging of the upper extremity. The direction of flow can also be depicted with PC imaging and may be helpful verifying the presence of functionally significant vascular pathology.
Multidetector CT and three-dimensional CT angiography of upper extremity arterial injury
Extracellular contrast agents have a short blood pool half-life and are best suited for arterial-phase or early delayed-phase imaging. This makes the need for accurate bolus timing important. The limitations of imaging with extracellular agents led to the development of intravascular contrast agents with a prolonged intravascular half-life, referred to as blood pool contrast agents. Gadofosveset trisodium Lantheus Medical Imaging, North Billerica, Massachusetts binds reversibly to human serum albumin, which effectively prolongs the serum half-life to several hours.
As with other extracellular contrast agents, first-pass MRA can be performed with gadofosveset. The main advantage of gadofosveset is the ability to perform steady state imaging that is helpful for facilitating delayed imaging using provocative maneuvers, such as arm position, to evaluate for thoracic outlet syndrome. The contrast agent should be injected at a minimum rate of 1. Injecting the contrast agent in the contralateral extremity from that with suspected pathology avoids susceptibility artifacts due to high concentrations of gadolinium during first pass of the injection in the symptomatic extremity Fig.
Extremity Arteriography: Purpose and Procedure
In some circumstances, it may be necessary to inject from a foot vein or femoral central venous access. Dilution of contrast may also be helpful when small volumes of contrast eg, with an infant or small child are needed and are difficult to handle using power injectors. Dilution also mitigate susceptibility related artifacts from highly concentrated contrast. Patient comfort is of paramount importance to ensure a successful examination with minimal motion artifact.
Feet-first imaging may be recommended for claustrophobic patients, but head-first imaging allows the injection site to be monitored and is preferable.
For upper arm imaging, patients should be positioned supine with the arm next to the body. The arm and site of interest should be moved as close as possible to the center of the magnet. For forearm and hand imaging, patients should be positioned in a decubitus prone position, with the arm of interest extended above the head superman position. The arm and region of interest should be positioned within the extremity coil as close to the center of the magnet as possible.
In cases of clinically suspected vasospasm, wrapping the hand in a warm towel may be helpful in depicting the peripheral digital vessels. When the hand is imaged, the palm should lie flat within the coil with the fingers slightly spread to include the entire arterial tree in the imaging volume. Imaging of the proximal upper extremity should be performed with phased-array receive coils.
In general, a single-phase MRA can be performed for imaging of the proximal upper extremity; however, time-resolved MRA can also be performed to assess the flow dynamics. The authors use a 3-D spoiled gradient-echo sequence with a repetition time TR of 3. Zero-filling in the in-plane and through plane direction is recommended to avoid stair-step artifacts when performing multiplanar reformatting MPR. Imaging of the forearm should be performed with dedicated phased-array extremity coils.
The authors use either an 8-element cardiac coil or element extremity wrap coils.
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In general, a time-resolved MRA should be performed for imaging of the forearm. The authors recommend performing the excitation in sagittal orientation to avoid foldover wrapping artifacts from the body. Zero-filling is performed to facilitate interpolation, necessary to performing MPRs. Imaging of the hand should be performed with dedicated phased-array extremity coils. The authors use a element extremity wrap coil or a quadrature knee coil. In general, a time-resolved MRA should always be performed for imaging of the hand.