Endovascular aortic aneurysm repair (EVAR) is evolving into a viable alternative to open surgical repair for many patients with abdominal and thoracic aortic aneurysms. Endoleak development is a complication of EVAR and represents one of the limitations of this procedure. Endoleaks represent blood flow outside the stent-graft lumen but within the aneurysm sac. Lifelong imaging surveillance of patients after EVAR is critical to detect endoleaks for the patient's benefit and to determine the long-term performance of the stent-graft. Although computed tomographic angiography is the most commonly used examination for imaging surveillance, magnetic resonance angiography, ultrasonography, and digital subtraction angiography all have a role in endoleak detection and management. This review will focus on imaging techniques used for endoleak detection and the role imaging surveillance plays in the overall care of the post-EVAR patient.

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A fast spin-echo sequence weighted with a time constant that defines the magnetic relaxation of spins under the influence of a radio-frequency field (T1(rho)) was used in six subjects to measure magnetic resonance (MR) relaxation times in the knee joint with a 1.5-T MR imager. A quantitative comparison of T2- and T1(rho)-weighted MR images was also performed. Substantial T1(rho) dispersion was demonstrated in human articular cartilage, but muscle did not demonstrate much dispersion. T1(rho)-weighted images depicted a chondral lesion with 25% better signal-difference-to-noise ratios than comparable T2-weighted images. This technique may depict cartilage and muscular abnormalities.

Purpose: To measure T 1 relaxation times and T 1 dispersion in the human brain in vivo. Materials and Methods:Magnetic resonance imaging (MRI) was performed on a 1.5-T GE Signa clinical scanner using the standard GE head coil. A fast spin-echo (FSE)-based T 1 -weighted MR pulse sequence was employed to obtain images from five healthy male volunteers. Optimal imaging parameters were determined while considering both the objective of the study and the guarantee that radio-frequency (RF) power deposition during MR did not exceed Food and Drug Administration (FDA)-mandated safety levels.Results: T 1 -weighted MR images showed excellent contrast between different brain tissues. These images were less blurred than corresponding T 2 -weighted images obtained with similar contrast, especially in regions between brain parenchyma and cerebrospinal fluid (CSF). Average T 1 values for white matter (WM), gray matter (GM), and CSF were 85 Ϯ 3, 99 Ϯ 1, and 637 Ϯ 78 msec, respectively, at a spin-locking field of 500 Hz. T 1 is 30% higher in the parenchyma and 78% higher in CSF compared to the corresponding T 2 values. T 1 dispersion was observed between spin-locking frequencies 0 and 500 Hz.Conclusion: T 1 -weighted MRI provides images of the brain with superb contrast and detail. T 1 values measured in the different brain tissues will serve as useful baseline values for analysis of T 1 changes associated with pathology.

Purpose: To design and implement a magnetic resonance imaging (MRI) pulse sequence capable of performing threedimensional T 1 -weighted MRI on a 1.5-T clinical scanner, and determine the optimal sequence parameters, both theoretically and experimentally, so that the energy deposition by the radiofrequency pulses in the sequence, measured as the specific absorption rate (SAR), does not exceed safety guidelines for imaging human subjects. Materials and Methods:A three-pulse cluster was preencoded to a three-dimensional gradient-echo imaging sequence to create a three-dimensional, T 1 -weighted MRI pulse sequence. Imaging experiments were performed on a GE clinical scanner with a custom-built knee-coil. We validated the performance of this sequence by imaging articular cartilage of a bovine patella and comparing T 1 values measured by this sequence to those obtained with a previously tested two-dimensional imaging sequence. Using a previously developed model for SAR calculation, the imaging parameters were adjusted such that the energy deposition by the radiofrequency pulses in the sequence did not exceed safety guidelines for imaging human subjects. The actual temperature increase due to the sequence was measured in a phantom by a MRI-based temperature mapping technique. Following these experiments, the performance of this sequence was demonstrated in vivo by obtaining T 1 -weighted images of the knee joint of a healthy individual. Results:Calculated T 1 of articular cartilage in the specimen was similar for both and three-dimensional and twodimensional methods (84 Ϯ 2 msec and 80 Ϯ 3 msec, respectively). The temperature increase in the phantom resulting from the sequence was 0.015°C, which is well below the established safety guidelines. Images of the human knee joint in vivo demonstrate a clear delineation of cartilage from surrounding tissues. Conclusion:We developed and implemented a three-dimensional T 1 -weighted pulse sequence on a 1.5-T clinical scanner.