Gadolinium-enhanced magnetic resonance angiography of abdominal aortic aneurysms

Coronary MR angiography

MR angiography of the coronary arteries became possible in 1991 with the development of a new group of fast MR imaging sequences. Although the role of coronary MR angiography in screening for coronary artery lesions has not yet been established, coronary MR angiography already has been very successful in the detection of coronary artery variants and the imaging of coronary stents and bypass grafts. Variants of these new MR imaging techniques also can quantitate velocity in native coronary arteries. Several generations of coronary MR angiographic techniques exist; all techniques use EKG-triggering. The use of MR contrast agents appears to further improve all techniques. Technical progress and changes in this subfield of cardiac MR imaging have been so fast that large-scale preclinical trials have not been conducted with the majority of the first and second generation coronary MR angiographic pulse sequences as known today. This article reviews the development of these new cardiac MR imaging techniques and the initial successes with clinical application using commercial MR scanners.

Renal artery stenosis: evaluation with conventional angiography versus gadolinium-enhanced MR angiography

PURPOSE

To evaluate the interobserver and intermodality variability of conventional angiography and gadolinium-enhanced magnetic resonance (MR) angiography in the assessment of renal artery stenosis.

MATERIALS AND METHODS

Fifty-four patients underwent conventional angiography and gadolinium-enhanced three-dimensional gradient-echo MR angiography. Three angiographers blinded to each other's interpretations and the MR angiographic findings assessed the conventional angiograms for renal artery stenosis. Similarly, three blinded MR imagers evaluated the MR angiograms.

RESULTS

Interobserver variability for the degree of renal artery stenosis in the 107 kidneys evaluated was not significantly different between the two modalities. The mean SD of the degree of stenosis was 6.9% at MR angiography versus 7.5% at conventional angiography (alpha < or = .05, P > .05). In 70 kidneys (65%), the average degree of stenosis reported by the readers for the two modalities differed by 10% or less. In 22 cases (21%), the degree of stenosis was overestimated with MR angiography by more than 10% relative to the results of conventional angiography. In 15 cases (14%), the degree of stenosis was underestimated with MR angiography by more than 10%.

CONCLUSION

Gadolinium-enhanced MR angiography permits evaluation of renal artery stenosis with an interobserver variability comparable with that of conventional angiography.

Gadolinium-enhanced three-dimensional MR angiography of the aorta and peripheral arteries: evaluation of a multistation examination using two gadopentetate dimeglumine infusions

OBJECTIVE

Three-dimensional gadolinium-enhanced MR angiography is a rapid and accurate method that can at times image only a limited amount of anatomy during an examination. We evaluated a technique that doubled the anatomy imaged by obtaining two separate gadolinium-enhanced MR angiograms during a single examination.

MATERIALS AND METHODS

Twenty-three patients referred for MR evaluation of aortic or peripheral vascular disease underwent two successive gadolinium-enhanced three-dimensional MR angiographic examinations during a single MR examination. An injection of 15 ml of gadopentetate dimeglumine was used for the first MR angiogram, and 25 ml was used for the second MR angiogram. The angiograms were quantitatively and qualitatively evaluated to determine the effect of residual gadolinium from the initial MR angiogram on the second angiogram.

RESULTS

The two studies depicted either the entire aorta to the femoral arteries (n = 10) or the distal aorta to the popliteal arteries (n = 13). The total mean gadolinium dose was 0.245 mmol/kg per patient. An average of 15 min elapsed between injections. The value of arterial signal-to-noise ratio (mean, 48.8 versus 56.4) and artery-to-vein contrast-to-noise ratio (mean, 45.5 versus 49.0) increased between the first and second angiograms, respectively. Residual gadolinium elevated the values for venous signal-to-noise ratio (mean, 2.3 versus 7.2) and background-to-muscle signal-to-noise ratio (mean, 5.5 versus 10.1) on the second MR angiogram. Qualitative evaluation by three observers showed no significant differences in diagnostic usefulness or overall image quality between the first and second MR angiograms.

CONCLUSION

The use of two low-dose gadolinium-enhanced three-dimensional MR angiograms during a single examination is a feasible approach to increase anatomic coverage when performing gadolinium-enhanced three-dimensional MR angiography of the aorta and peripheral vessels. Although background enhancement is slightly elevated on the second angiogram, such enhancement does not significantly change diagnostic usefulness or overall image quality.

Renal anatomic changes on magnetic resonance imaging and gadolinium-enhanced magnetic resonance angiography after renal revascularization. Original investigation

RATIONALE AND OBJECTIVES

The anatomic and hemodynamic renal changes after renal arterial revascularization (RAR) were investigated.

METHODS

Thirty-seven kidneys and 40 renal arteries were evaluated in 20 patients by using magnetic resonance imaging/magnetic resonance angiography (MRI/MRA) to assess pre- and post-RAR renal length and mass, parenchymal thickness, renal enhancement, renal artery caliber, poststenotic dilation, and signal dephasing on 3D phase contrast (PC). The kidneys and renal arteries were segregated into three groups. Group 1 included 16 patients who benefited from RAR (defined as clinical improvement based on decreased serum creatinine or fewer number of antihypertensive medications) in whom 26 renal arteries in 25 kidneys were studied. Intervention included renal artery endarterectomy (n = 20); aortorenal bypass (n = 3); renal artery reimplantation (n = 3); and percutaneous transluminal angioplasty (PTA; n = 1). A total of 27 interventions was performed, as PTA failed for one patient who subsequently underwent aortorenal bypass before reimaging. Group 2 included four patients who did not clinically benefit. A total of eight revascularized arteries were studied in seven kidneys. In group 3, six renal arteries in five kidneys from groups 1 and 2 without RAS/RAR were analyzed as an internal control.

RESULTS

Technical success (defined as increased vessel caliber after intervention) was achieved in 33 of the 34 revascularized arteries. A statistically significant increase in renal length occurred regardless of clinical outcome (pre-RAR, 9.5 cm; post-RAR, 10.5 cm; P < 0.0001). Parenchymal thickness and renal mass, however, improved only in patients who benefited clinically from RAR. Parenchymal enhancement was unchanged in any of the groups studied. No significant morphologic changes were detected in the control group.

CONCLUSIONS

Magnetic resonance imaging and Gd-MRA detect anatomic and hemodynamic changes that occur with renal revascularization.

Magnetic resonance angiography of lower-extremity arterial disease

Improvements in vascular technique have expanded the treatment options for patients with severe occlusive peripheral vascular disease. The decision to perform a major revascularization procedure in patients who are often at high risk for cardiovascular morbidity and mortality depends on the risk-benefit ratio. Detailed and accurate vascular imaging is essential and evaluating the likelihood of a successful revascularization with subsequent limb salvage. Although contrast angiography has been the time-honored reference standard imaging technique, the method is an invasive procedure with limitations and risks. MRA is a new, noninvasive vascular imaging technique that may now be added to the imaging options with the potential for improved sensitivity for finding patent runoff vessels, avoidance of morbidity, and cost equivalent to that of conventional contrast angiography. Magnetic resonance angiography is a rapidly developing and exciting new vascular imaging technique. As with any new technique, it is imperative that individual centers validate their MRA results and interpretations against the time-honored standard, which continues to be contrast arteriography. Several studies now indicate that MRA can be a cost-effective outpatient imaging technique sufficient for planning and successfully performing peripheral bypass procedures. As developments in hardware, software, and non-nephrotoxic contrast agents continue to increase, applicability of MRA in vascular surgery will continue to expand. Predictably, MRA will have a major role in the future of vascular imaging, and it is likely to supplant the need for conventional contrast angiography in the majority of patients.

Dynamic gadolinium DTPA-enhanced magnetic resonance of intravascular stents

RATIONALE AND OBJECTIVES

Magnetic resonance contrast enhancement depends on the timing of image acquisition. Human trials have demonstrated efficacy of renal artery stents on salvage of renal function. This study assessed the ability of dynamic gadolinium (Gd)-DTPA administration to demonstrate renal and iliac artery stent patency compared to conventional angiography as the gold standard.

METHODS

Seven subjects with eight stents referred for angiography underwent dynamic magnetic resonance studies, all with renal artery stenting. All were examined with conventional angiography and after dynamic Gd-DTPA infusion. Coronal magnetic resonance images were acquired using a GE Signa 1.5 T magnet (fast spoiled gradient echo; echo time = 4.2 ms; repetition time = 68-150 ms; flip angle = 75 degrees) 0 to 600 seconds after 0.1 mmol/Kg Gd-DTPA intravenous bolus injection during sequential breath-hold acquisitions 13 to 32 seconds each.

RESULTS

All eight stents were visualized with 100% accurate patency documentation.

CONCLUSIONS

Fast spoiled gradient echo magnetic resonance imaging with bolus Gd-DTPA administration can provide adequate time and spatial resolution to demonstrate arterial stent patency.

Contrast-enhanced 3D MRA with centric ordering in k space: a preliminary clinical experience in imaging the abdominal aorta and renal and peripheral arterial vasculature

The objective of this study was to determine the clinical utility of a contrast-enhanced, centric reordered, three-dimensional (3D) MR angiography (MRA) pulse sequence in imaging the abdominal aorta and renal and peripheral lower extremity arteries. Twenty-eight MRA studies were performed on 23 patients and four volunteers at 1.5 T using a 3D contrast-enhanced, centric reordered pulse sequence. In 20 patients, the abdominal aorta and renal arteries were imaged, and in seven patients, the lower extremity arteries were imaged. In 19 patients, a total of 51 renal vessels were evaluated (33 renal arteries using .1 mmol/kg of gadopentetate dimeglumine and 18 renal arteries using .2 mmol/kg of gadoteridol). A total of 70 peripheral arterial segments were assessed using .2 mmol/kg of gadoteridol. Correlation with conventional angiography was made for the following 14 cases: renal artery stenosis (four cases), abdominal aortic stenosis (one case), arteriovenous fistula in a transplant kidney (one case), renal arteriovenous malformation (one case), common iliac artery aneurysms (one case), and peripheral lower extremity (six cases). Of the 70 peripheral arterial segments evaluated, in 35, there was correlation with x-ray angiography. The mean percent of aortic signal enhancement was significantly higher in the .2 mmol/kg dose group (370.8 +/- 190.3) than in the .1 mmol/kg dose group (184.5 +/- 128.9) (P = .02). However, there was no apparent difference between the two doses for visualization of the renal and accessory renal arteries. There was concordance between the contrast-enhanced 3D MRA studies and conventional angiography in all cases of renal artery and peripheral arterial stenoses and occlusions, including visualization of reconstituted peripheral arterial segments. There was no evidence of spin dephasing effects at sites of stenoses on the 3D contrast-enhanced MRA studies. Contrast-enhanced, centric reordered, 3D MRA can rapidly image the abdominal aorta and renal and accessory renal arteries, as well as peripheral lower extremity arteries, with high resolution. Accurate depiction of the vascular lumen at sites of stenosis is made because of the lack of spin dephasing effects, even with hemodynamically significant stenoses. Additional larger clinical trials are required with this promising technique.

Role of magnetic resonance angiography for assessment of abdominal aortic aneurysm before endoluminal repair

BACKGROUND

A detailed knowledge of the morphology of the aorta and iliac arteries is an important prerequisite for successful endoluminal abdominal aortic aneurysm (AAA) repair. The best method of preoperative evaluation remains to be determined.

METHODS

A prospective study was undertaken between January 1994 and July 1995 to assess the ability of computed tomography (CT), magnetic resonance angiography (MRA), colour duplex imaging and intra-arterial digital subtraction angiography (IA-DSA) to visualize AAA morphology.

RESULTS

Eighty-two consecutive patients (64 men, 18 women) with AAA were assessed with MRA, contrast-enhanced CT, colour duplex imaging and IA-DSA. Median age was 74 (range 59-87) years and median AAA diameter was 5.7 (range 3.5-9.7) cm. Five patients were unable to tolerate CT or MRA examination. Seventy-seven patients underwent both CT and MRA. Of these, 55 also had a colour duplex scan and 32 underwent arteriography. The scans were assessed by an independent blinded observer. MRA was significantly better (P < 0.01) at visualizing AAA morphology compared with CT and colour duplex imaging. There was no statistically significant difference between MRA and arteriography.

CONCLUSION

MRA is useful in patient selection for endoluminal AAA repair, as it avoids use of iodinated contrast medium and ionizing radiation.

Magnetic resonance imaging and MR angiography of endoluminally treated abdominal aortic aneurysms

OBJECTIVES

To evaluate magnetic resonance imaging (MRI) with gadolinium-based contrast medium-enhanced MR angiography (MRA) for the follow-up of endoluminally treated abdominal aortic aneurysms.

DESIGN

MRI/MRA, angiography and computed tomography (CT) were performed 1 month after endoluminal stent-graft placement. MRI/MRA was repeated at 6 and 12 months and angiography and CT were added to confirm unexpected findings.

MATERIALS

Fifteen male patients with endoluminally treated abdominal aortic aneurysms.

METHODS

MRI with MRA, spiral CT with transverse images and angiography were performed.

RESULTS

MRI/MRA demonstrated changes of stent-graft morphology, aortic neck- and aneurysmal diameter, stent-graft blood flow, stent-graft leakage, blood flow in lumbar arteries, intra-aneurysmal thrombus, periaortic inflammation and vertebral body infarction. For most of these features MRI/MRA provided more information than angiography and/or CT. MRI was the only method demonstrating thrombus reorganisation and vertebral body infarction.

CONCLUSIONS

MRI with MRA provides the relevant information needed for follow-up of endoluminally treated abdominal aortic aneurysms (AAA). This may be the method of choice because of its use of contrast media with very low nephrotoxicity, lack of ionising radiation and non-invasiveness.

Standard dose Gd-DTPA dynamic MR of renal arteries

Renal MR contrast enhancement depends on the timing of image acquisition. Limited human trials have demonstrated efficacy of renal artery stents on salvage of renal function. This study assessed the ability of dynamic gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) administration to demonstrate renal artery stenosis and renal stent patency compared to conventional angiography as the gold standard. Twenty subjects referred for renal angiography underwent 22 dynamic MR studies, including 7 with renal artery stenting (Palmaz P204 or P201, Johnson & Johnson, Sydney, Australia). All were examined with conventional angiography and after dynamic Gd-DTPA infusion. Coronal MR images of the kidneys were acquired using a GE Signa 1.5-T magnet (General Electric Medical Systems, Milwaukee, WI) (fast spoiled gradient echo [FSPGR]; TE=4.2 msec, TR=68-150 msec, flip angle=75 degrees) 0 to 600 seconds after iv bolus injection of 15 ml of Gd-DTPA during sequential breath-hold acquisitions, 13 to 32 seconds each. All 51 renal arteries (13 stenosed, 38 normal) were detected with dynamic MRI. Severity of renal artery stenosis was classified correctly with an accuracy of 98% (95% confidence interval [CI]: 85-100), yielding 98% specificity and 100% sensitivity. All nine renal stents were visualized with 100% accurate patency documentation. FSPGR MRI with bolus Gd-DTPA administration can provide adequate time and spatial resolution to demonstrate renal artery stenosis.

Intravascular contrast agent improves magnetic resonance angiography of carotid arteries in minipigs

This study was designed to optimize three-dimensional (3D) time-of-flight (TOF) magnetic resonance angiography (MRA) sequences and to determine whether contrast-enhanced MRA could improve the accuracy of lumen definition in stenosed carotid arteries of minipigs. 3D TOF MRA was acquired with use of either an intravascular (n = 13) and/or an extravascular contrast agent (n = 5) administrated at 2 to 4 weeks after balloon-induced injury to a carotid artery in 16 minipigs. Vascular contrast, defined as signal intensity differences between blood vessels and muscle normalized to the signal intensity of muscle, was compared before and after the injection of each contrast agent and between the two agents. Different vascular patencies were observed among the animals, including completely occluded vessels (n = 5), stenotic vessels (n = 3), and vessels with no visible stenosis (n = 8). Superior vascular contrast improvement was observed for small arteries and veins and for large veins with the intravascular contrast agent when compared with the extravascular contrast agent. In addition, preliminary studies in two of the animals showed a good correlation for the extent of luminal stenosis defined by digital subtraction angiography compared with MRA obtained after administration of the intravascular contrast agent (R2 = .71, with a slope of .96 +/- .04 by a linear regression analysis). We concluded that use of an intravascular contrast agent optimizes 3D TOF MRA and may improve its accuracy compared with digital subtraction angiography.

Preoperative sizing of grafts for transfemoral endovascular aneurysm management: a prospective comparative study of spiral CT angiography, arteriography, and conventional CT imaging

PURPOSE

To define the impact of spiral computed tomographic angiography (CTA) with image reconstruction on graft selection for Transfemoral Endovascular Aneurysm Management (TEAM) by comparing it to conventional computed tomography (CT) and contrast arteriography.

METHODS

Twenty-one candidates for TEAM were included. The diameters of the superior and inferior aneurysm necks and lengths between the graft attachment sites were measured using the three imaging techniques. These measurements and their consequences on graft selection were studied.

RESULTS

The difference in length sizing between spiral CTA and arteriography never exceeded 1 cm; however, lengths measured by conventional CT scanning resulted in underestimation of graft length in 91% of patients. Graft diameters were chosen too small in 62% of the patients when based on arteriographic diameter measurements. A graft of similar diameter was selected by spiral CTA and conventional CT scanning in 81% of the patients, while minor oversizing by conventional CT scanning was found in 14%.

CONCLUSIONS

Neither conventional CT scanning nor arteriography is adequate as a sole preoperative radiological investigation for TEAM graft sizing. Spiral CTA with image processing produces all information required for selection of the optimal graft size and should be regarded the method of first choice for this purpose.

Morphologic assessment of abdominal aortic aneurysms by spiral computed tomographic scanning

PURPOSE

The aim of this study was to seek a relationship between the morphologic features of abdominal aortic aneurysms and the feasibility of endoaortic grafting.

METHODS

Between June 1995 and January 1996, 86 patients were prospectively studied with contrast-enhanced spiral computed tomographic scans, which provided 35 parameters concerning the aorta and iliac arteries. Four groups were established according to the diameter of abdominal aortic aneurysms: group A, 40 to 49 mm, 36 patients; group B, 50 to 59 mm, 26 patients; group C, 60 to 69 mm, 10 patients; and group D, greater than 70 mm, 14 patients.

RESULTS

There was a correlation between the diameter and length of the aneurysm (p < 0.0001) and between aneurysm diameter and length of the proximal neck (p < 0.001). Presence of a proximal neck or a distal neck was more frequent in groups A and B than in groups C and D (p < 0.01). The feasibility of endovascular grafting was estimated at between 50% and 61.6% and was higher in groups A and B than in groups C and D (p < 0.01).

CONCLUSIONS

This study has shown an inverse relationship between the diameter of the aneurysm and the length of the aortic neck (correlation coefficient, -0.3640, p < 0.001). The diameter of an aneurysm was the most useful of the 31 parameters measured in predicting the feasibility of endoaortic grafting, estimated at 71% for aneurysms less than 60 mm in diameter and 37.5% for aneurysms greater than 60 mm in diameter (p < 0.01).

Contrast-enhanced, K-space-centered, breath-hold MR angiography of the renal arteries and the abdominal aorta

The purpose of this study was to evaluate the capability of contrast-enhanced breath-hold fast imaging with steady-state precession (FISP) three-dimensional MR angiography (MRA) to detect stenotic lesions of the abdominal aorta, the renal arteries, and the iliac arteries by using a K-space-centered 20-ml gadolinium-diethylene pentaacetic acid (Gd-DTPA) bolus. Fifty patients were studied before conventional x-ray angiography. Contrast-enhanced breath-hold FISP three-dimensional MRA was applied in the coronal view, centered at the renal arteries. Twenty ml of Gd-DTPA was used in all subjects. A test bolus was applied to determine the injection time for the K-space-centered bolus injection. Of 300 segments, 284 segments were classified correctly, 11 were overestimated, and five were underestimated. Sensitivity was 98%, specificity was 96%, positive predictive value was 96%, negative predictive value was 98%, and accuracy was 97%. Of the 50 patients studied, 43 were staged correctly. No venous overlay was seen in 31 patients; partial overlay was seen in 16 patients, and venous structure overlay obscuring arterial anatomy was found in two patients. Six of nine accessory renal arteries could be identified by MRA. Intraobserver variability was .94. This study has shown the ability of contrast-enhanced breath-hold FISP three-dimensional MRA to detect and grade vascular lesions in the abdominal aorta and the renal arteries. The method may serve as a screening tool in the future.

Mesenteric revascularization during aneurysmectomy

The most important association between aortic aneurysm surgery and the mesenteric circulation is the potential for inadvertent compromise to the mesenteric trunks and their end organs. Preservation of visceral blood flow is a critical objective in each case, using methods that have been developed as techniques for suprarenal abdominal and thoracoabdominal aneurysmectomy have evolved. Beyond simply preserving what existed, revascularization by endarterectomy or bypass has a role in selected cases to improve the natural history of advanced mesenteric occlusive disease, although the rationale for such prophylactic surgery must remain relatively weak until more is learned about disease progression in the visceral arteries. Finally, a small number of patients with mesenteric ischemic symptoms at the time of aneurysmectomy clearly benefit from combined surgery.

MR angiography with an ultrasmall superparamagnetic iron oxide blood pool agent

The purpose of the study was to investigate the use of a dextran-coated ultrasmall superparamagnetic iron oxide (USPIO) as a blood pool contrast agent for thoracic and abdominal MR angiography. Abdominal and thoracic MR angiography was performed in six healthy volunteers using two-dimensional and three-dimensional spoiled gradient echo (SPGR) sequences before and after intravenous administration of USPIO. Doses ranged from 1.1 to 2.6 mg Fe/kg. Flip angle was varied from 20 to 60 degrees. Subjective image quality, analysis of signal-to-noise ratio (SNR), and blood T1 relaxation times were measured. USPIO significantly lowered the T1 of blood (from 1,210 ms precontrast to 159 ms postcontrast at a dose of 2.6 mg Fe/kg) (P < .01). Image quality on coronal fast three-dimensional breath-hold SPGR images of the abdomen increased with increasing dose and was maximum at the highest dose, producing an aortic SNR of 9.6 compared to 1.8 precontrast. Axial two-dimensional time-of-flight (TOF) aortic SNR was reduced significantly from 13 on precontrast to 6 on the postcontrast images at the highest dose (P < .05) due to T2* shortening effects. There was little flip angle dependence on image quality. Due to the T1 shortening effect and long intravascular half-life, USPIO improved visualization of vascular anatomy using three-dimensional fast SPGR imaging. The echo time must be minimized to minimize signal loss from T2* shortening effects. The blood pool distribution of USPIO is useful for equilibrium-phase MR angiography.

Gadolinium-enhanced magnetic resonance angiography of renal transplants

Our purpose was to investigate three-dimensional (3D) gadolinium-enhanced magnetic resonance angiography (Gd-MRA) in the evaluation of renal transplant arteries. Eleven MR angiography examinations were performed in nine renal transplant patients. Gd-MRA, three-dimensional phase contrast (3D-PC) post-gadolinium, and two-dimensional time-of-flight (2D-TOF) MR angiography were performed and independently reviewed by three vascular radiologists who, for each MR angiography sequence, separately graded occlusive disease in the ipsilateral iliac artery, the transplant artery anastomosis, and the transplant artery itself. The Gd-MRA and 3D-PC data were reviewed as maximum intensity projections (MIP) reconstructed in standard planes, and the 2D-TOF data were interpreted from source images. In addition, a single vascular radiologist prospectively interpreted the Gd-MRA and 3D-PC data together, hereinafter Gd/PC, from MIP reconstructions for each case. In all of these patients either surgical (n = 3) or angiographic studies (n = 8) were performed within 21 days following the MR examination, which served as a reference standard to determine sensitivity and specificity. The sensitivity/specificity for the detection of significant stenosis were as follows: Gd-MRA, 67/88; 3D-PC, 60.3/76.6; 2D-TOF, 47/81; and Gd/PC, 100/100. The kappa statistic (kappa) for interobserver agreement for the grading of stenoses by 2D-TOF, Gd-PC, and Gd-MRA was 0.48, 0.60, and 0.74, respectively. The percentage of all vascular segments seen well enough to grade (cumulative for all three observers) was 94%, 85%, and 79% for Gd-MRA, 3D-PC, and 2D-TOF, respectively. The combination of Gd-MRA and 3D-PC is a promising approach to the evaluation of transplant renal arteries.

Contrast-enhanced magnetic resonance angiography of carotid arterial wall in pigs

This study was designed to investigate the effects of contrast agents on MR images of balloon-injured carotid arteries containing atherosclerotic-like lesions. We have evaluated an intravascular contrast agent, MS-325 (METASYN INC., Cambridge, MA) and an extravascular contrast agent, Optimark, (Mallinckrodt Medical Inc., St. Louis, MO) on MR angiograms obtained 4 weeks after balloon hyperinflation-induced injury of the left common carotid artery in 12 hypercholesterolemic minipigs. High in-plane resolution (.8 x .4 mm2), thin slice (1 mm) time-of-flight gradient echo sequences were used to acquire the MR angiographic images. Vascular lumen definition was compared before and after a single bolus intravenous injection of a contrast agent. Digital subtraction angiograms were obtained from all pigs after MR imaging. High grade stenosis developed in 1 of the 12 pigs and five pigs had complete occlusion of the injured vessel. The remaining pigs exhibited essentially no visible stenoses as assessed either by MR angiography or digital subtraction angiography. The vessel walls of the stenosed and occluded vessels were visible after the injection of either intravascular or extravascular contrast agent. Histologic analyses showed well developed neovascularization in the neointima or occlusive thrombosis. We conclude that the observed contrast-enhanced vessel wall is caused by an increased vascular supply associated with thrombosis and neointimal thickening that leads to an accumulation of contrast agent in the abnormal vessel walls after the injection of the T1-shortening paramagnetic contrast agent.

Evaluation of the iliac arteries: comparison of two-dimensional time of flight magnetic resonance angiography with cardiac compensated fast gradient recalled echo and contrast-enhanced three-dimensional time of flight magnetic resonance angiography

We compared dynamic contrast-enhanced three-dimensional time of flight (3DTOF) magnetic resonance angiography (MRA) with two-dimensional time of flight (2DTOF) MRA with cardiac compensated fast gradient recalled echo (C-MON) and conventional angiography (CA) when it was available. C-MON re-orders the normal data acquisition to minimize ghosting artifacts generated by pulsatile flow. The initial phase of the study involved optimization of parameters and comparison C-MON with no C = MON in eight patients and volunteers. The final phase of the study involved 53 patients who were imaged with contrast-enhanced 3DTOF MRA and 2DTOF MRA with C-MON. Thirty of these patients also had CA. In the initial phase, 2DTOF MRA with C-MON was found to be equal (n = 3) or superior (n = 5) to 2DTOF without C-MON. In the final phase, the agreement among all imaging modalities varied from substantial to almost perfect (Cohen's kappa = .6-.83). The lowest agreement was using 2DTOF to evaluate the external iliac segments. The among suggested treatments varied from substantial to almost perfect for all imaging modalities (Cohen's kappa = .73-93). The diagnostic efficacies of 2DTOF with C-MON and contrast-enhanced 3DTOF were high overall, with the lowest value being a specificity of 63% for one reader in the evaluation of an external iliac segment using 2DTOF. In summary, 2DTOF with C-MON helped to eliminate artifacts due to pulsatility in the iliac arterial segments. In our experience, both dynamic contrast-enhanced 3DTOF MRA and 2DTOF MRA with C-MON performed well in the evaluation of the iliac arteries. Both studies have high interobeserver agreement and high diagnostic efficacy. Contrast-enhanced 3DTOF MRA should be reserved for situations in which the iliac vessels are extremely tortuous or occluded or the external iliac segments are poorly seen.

Magnetic resonance angiography of the aortic arch

Duplex ultrasound and magnetic resonance angiographic (MRA) studies are the principal noninvasive methods for evaluation of extracranial occlusive disease in patients at risk for stroke, but each has limited ability to diagnose aortic arch and arch vessel disease. Recent favorable reports of the nonnephrotoxic contrast agent Gadolinium (Gd) being used to enhance MRA images of the abdominal aorta prompted us to examine its utility for the aortic arch vessels. Prospectively, 28 patients with suspected carotid or arch vessel disease were imaged by contrast arteriographic examination and MRA + Gd of the aortic arch within 30 days of each other. One (for contrast arteriograms) or two (for MRA) blinded readers measured stenoses with the contrast arteriograms as the standard. A total of 196 arch vessels containing 58 stenoses and four occlusions (by arteriogram) were examined with each method. Interobserver agreement for interpretation of MRA studies was substantial (kappa = 0.68). MRA detected all anatomic anomalies (e.g., bovine arch). The correlation of MRA with arteriographic scans for arch vessel stenoses > 50% was sensitivity, 73% (readers 1 and 2); specificity, 98% (reader 1), 89% (reader 2); positive predictive value, 73% (reader 1), 89% (reader 2); negative predictive value, 98% (readers 1 and 2); accuracy, 97% (reader 1), 98% (reader 2). MRA + Gd is an accurate new noninvasive imaging method for detection of significant aortic arch disease. In its current state of development, however, it cannot obviate the need for contrast arteriographic examination.

Comparison of magnetic resonance imaging measurements of abdominal aortic aneurysms with measurements obtained by other imaging techniques and intraoperative measurements: possible implications for endovascular grafting

PURPOSE

Abdominal aortic aneurysm morphologic evaluation with conventional imaging techniques is inadequate when endovascular repair is being contemplated. This study has addressed the problem with magnetic resonance imaging (MRI).

METHODS

Twenty patients (14 men, 6 women) with a median age of 73 years were recruited and assessed according to current endovascular graft selection criteria. Thirteen patients subsequently underwent open aneurysmorrhaphy, and the intraoperative parameters have been compared with those of duplex ultrasonography and MRI.

RESULTS

No significant difference was demonstrated in the diameter of the infrarenal neck among ultrasonography, MRI, and intraoperative findings (p > 0.05, Mann Whitney U Test) and also during assessment of infrarenal neck length; however, duplex sonography accurately defined the renal ostia in only five cases. MRI visualized 38 of 40 renal arteries. Distal aortic involvement (cuff diameter and length) and the length and diameter of the common iliac arteries were accurately determined by MRI in all cases, and no significant difference was demonstrated with the intraoperative findings. Comparison of the intraoperative and MRI aneurysm lengths suggested a slight trend of overestimation by MRI resulting from angulation of the aneurysm, but this figure did not reach statistical significance. Only two patients met the current criteria for endoluminal straight grafting.

CONCLUSIONS

Both MRI and duplex sonography accurately predicted aortic morphologic characteristics; however, MRI provided the most comprehensive anatomic picture for patient selection and should be considered the nonionizing imaging modality of choice when an endovascular repair is being contemplated.

Clinical experience with a bifurcated endovascular graft for abdominal aortic aneurysm repair

PURPOSE

The purpose of this study was to test a transfemoral system of bifurcated endovascular graft insertion for aortic aneurysm repair.

METHODS

Bifurcated endovascular grafts were inserted through bilateral femoral artery cutdowns in 41 patients. The results were assessed by completion angiography and follow-up computed tomography.

RESULTS

The second half of the study included more aneurysms 6 cm or larger (p < 0.05) and more instances of short proximal neck (p < 0.05), proximal neck angulation (p < 0.05), and iliac angulation (p < 0.05). Despite the increasingly challenging anatomy, the results were better in the second half of the study as illustrated by the lower overall combined morbidity/mortality rate (15% vs 50%) and higher overall success rate (85% versus 65%). The mortality rate for the series as a whole was 7.5%. Mean follow-up was 18.8 months for the first 20 patients and 10.9 months for the second 20. The commonest complication in the first half of the study was graft thrombosis (n = 5). This complication was absent from the second half of the study because of routine adjunctive stenting. Two patients died of complications of endovascular repair. In both cases aneurysm rupture on the third postoperative day was associated with coagulopathy and angiographic signs of perigraft leak.

CONCLUSION

Aneurysm exclusion with a bifurcated endovascular graft was feasible in a wide range of patients, but when the aneurysm was not entirely excluded from the circulation, the risk of rupture persisted.

The effects of time varying intravascular signal intensity and k-space acquisition order on three-dimensional MR angiography image quality

The optimum infusion timing and k-space ordering for obtaining gadolinium-enhanced three-dimensional MR angiograms was determined through computer modeling using temporal contrast characteristics obtained from patient gadolinium infusion data. The effects of bolus timing were evaluated by varying the relationship between peak intravascular gadolinium concentration and the time at which the center of k space was acquired (tck) for sequential and centric acquisition techniques. Flow phantom experiments were performed to validate the theoretical computations. Gadolinium concentration at the time of central k-space acquisition determines intravascular signal intensity. Artifacts, including vessel broadening and edge ringing, depend on the order in which k space is collected and on how rapidly the gadolinium concentration changes. Artifacts are greatest when the center of k space is acquired before the intravascular gadolinium peak. Application of the optimal infusion timing results in preferential arterial enhancement with a minimum of artifacts in patients undergoing MR angiography.