MR Imaging Findings of Traumatic Thoracic Aortic Injury

PURPOSE: To determine the magnetic resonance imaging (MRI) findings in patients with traumatic thoracic aortic injury and to assess the usefulness of MRI for the diagnosis of aortic injury. MATERIALS AND METHODS: Between May 1990 and June 2000, sixteen patients with blunt thoracic aortic injury underwent MRI. The findings were evaluated with regard to the type of aortic injury, aortic circumference, the size, direction and shape of the pseudoaneurysm, the intimal flap, and pseudocoarctation. Six patients underwent follow-up MRI, and any changes in the findings were assessed. RESULTS: MRI indicated that traumatic thoracic aortic injury comprised localized pseudoaneurysm in 15 patients and extensive aortic dissection in one. The aortic circumference was partially involved in all cases. Pseudoaneurysms were located at the aortic isthmus in 16 cases and the descending thoracic aorta in one. Two patients each had two lesions: two pseudoaneurysms in one, and aortic dissection and pseudoaneurysm in the other. The mean diameter and length of the pseudoaneurysms was 2.8+/-0.8 cm (mean+/-SD) and 3.3+/-1.0 cm (mean+/-SD), respectively. Their direction was anteromedial or anterolateral in 15 cases and posterolateral in two. All were saccular shaped. An intimal flap was present in seven cases and pseudocoarctation was demonstrated in ten. Follow-up MRI revealed changes in the size of a pseudoaneurysm or the length of an aortic dissection. CONCLUSION: The most common finding demonstrated by MRI in patients with traumatic thoracic aortic injury was an anteromedially-directed saccular pseudoaneurysm in the aortic isthmus. This modality was considered useful for evaluation of the entire aorta in cases of multiple pseudoaneurysms or aortic dissection.

Contrast-Enhanced Magnetic Resonance Angiography: Dose the Test Dose Bolus Represent the Main Dose Bolus Accurately?

OBJECTIVE: To determine whether the time-intensity curves acquired by test and main dose contrast injections for MR angiography are similar. MATERIALS AND METHODS: In 11 patients, repeated contrast-enhanced 2D-turbo-FLASH scans with 1-sec interval were obtained. Both test and main dose time-intensity curves were acquired from the abdominal aorta, and the parameters of time-intensity curves for the test and main boluses were compared. The parame-ters used were arterial and venous enhancement times, arterial peak enhance-ment time, arteriovenous circulation time, enhancement duration and enhance-ment expansion ratio. RESULTS: Between the main and test boluses, arterial and venous enhance-ment times and arteriovenous circulation time showed statistically significant correlation (p < 0.01), with correlation coefficients of 0.95, 0.92 and 0.98 respectively. Although the enhancement duration was definitely greater than infusion time, reasonable measurement of the end enhancement point in the main bolus was impossible. CONCLUSION: Only arterial and venous enhancement times and arteriovenous circulation time of the main bolus could be predicted from the test-bolus results. The use of these reliable parameters would lead to improvements in the scan timing method for MR angiography.

Contrast-Enhanced Magnetic Resonance Angiography: Dose the Test Dose Bolus Represent the Main Dose Bolus Accurately?

OBJECTIVE: To determine whether the time-intensity curves acquired by test and main dose contrast injections for MR angiography are similar. MATERIALS AND METHODS: In 11 patients, repeated contrast-enhanced 2D-turbo-FLASH scans with 1-sec interval were obtained. Both test and main dose time-intensity curves were acquired from the abdominal aorta, and the parameters of time-intensity curves for the test and main boluses were compared. The parame-ters used were arterial and venous enhancement times, arterial peak enhance-ment time, arteriovenous circulation time, enhancement duration and enhance-ment expansion ratio. RESULTS: Between the main and test boluses, arterial and venous enhance-ment times and arteriovenous circulation time showed statistically significant correlation (p < 0.01), with correlation coefficients of 0.95, 0.92 and 0.98 respectively. Although the enhancement duration was definitely greater than infusion time, reasonable measurement of the end enhancement point in the main bolus was impossible. CONCLUSION: Only arterial and venous enhancement times and arteriovenous circulation time of the main bolus could be predicted from the test-bolus results. The use of these reliable parameters would lead to improvements in the scan timing method for MR angiography.

The Optimization of Scan Timing for Contrast-Enhanced Magnetic Resonance Angiography

OBJECTIVE: To determine the optimal scan timing for contrast-enhanced magnetic resonance angiography and to evaluate a new timing method based on the arteriovenous circulation time. MATERIALS AND METHODS: Eighty-nine contrast-enhanced magnetic resonance angiographic examinations were performed mainly in the extremities. A 1.5T scanner with a 3-D turbo-FLASH sequence was used, and during each study, two consecutive arterial phases and one venous phase were acquired. Scan delay time was calculated from the time-intensity curve by the traditional (n = 48) and/or the new (n = 41) method. This latter was based on arteriovenous circulation time rather than peak arterial enhancement time, as used in the traditional method. The numbers of first-phase images showing a properly enhanced arterial phase were compared between the two methods. RESULTS: Mean scan delay time was 5.4 sec longer with the new method than with the traditional. Properly enhanced first-phase images were found in 65% of cases (31/48) using the traditional timing method, and 95% (39/41) using the new method. When cases in which there was mismatch between the target vessel and the time-intensity curve acquisition site are excluded, erroneous acquisition occurred in seven cases with the traditional method, but in none with the new method. CONCLUSION: The calculation of scan delay time on the basis of arteriovenous circulation time provides better timing for arterial phase acquisition than the traditional method.

Aortic Arch Aneurysm: CT and MR Features

PURPOSE: The purpose of this study was to evaluate the CT and MR features of aortic arch aneurysms and todetermine the differences between involved segments and morphologic types according to their causes. MATERIALS AND METHODS: Twenty-nine patients with aortic arch aneurysms who underwent CT scanning(n=24) and/or MR imaging(n=16)were retrospectively evaluated. The aneurysms were analyzed with respect to location of involved segment,morphology, direction and size, and morphologic differences between aneurysms were compared according to causes. RESULTS: The causes of arch aneurysms were atherosclerosis in 25 patients(86%), trauma in three (10%) and infection in one (4%). Arch aneurysms were frequently located at the arch only(n=17,59%), ascending aorta toarch(n=6,21%), arch to descending aorta(n=4,14%), or ascending aorta to descending aorta(n=2,7%). The shape of theaneurysm was fusiform in 15 patients and saccular in 14. Atherosclerotic aneurysms(n=25) were fusiform in 15patients and saccular in ten. Arch aneurysms due to trauma and infection(n=4) were saccular. MRI was more helpfulthan CT scanning involved site, direction, and morphology of the aneurysm. CONCLUSION: Bothe CT scanning and MRIeasily diagnose arch aneurysms, though MRI is a very useful imaging modality for evaluating involved aorticsegments and morphologic types. Aortic arch aneurysms are either fusiform or saccular. Most saccular aneurysmsinvolve the aortic arch, whereas the involvement of fusiform aneurysms is more varied. Atherosclerosis is the mostcommon cause of both fusiform and saccular arch aneurysms.

Postoperative Assessment of Aortic Dissection: The Usefulness of MR Imaging and MR Angiography

PURPOSE: To demonstrate the usefulness of MR imaging and MR angiography in the evaluation of patients whohave undergone surgery for DeBakey type1 or 2 aortic dissection. MATERIALS AND METHODS: Nineteen patients who hadundergone surgery for DeBakey type I(n=13) or type II(n=6) aortic dissection were included in our study. Graftinterposition had been performed in 11 patients, ascending aorta replacement in five, and hemi-arch or total archreplacement in three. MRI was performed 3-40 months(mean:12.5) months after surgery. Twenty(turbo) spin-echo MRimages and 12 contrast-enhanced MR angiographs(3-D FISP) of 19 patients were retrospectively analyzed with regardto perigraft site(perigraft thickness or thrombus), graft site(anastomotic site, deformity of graft), status ofremnant false lumen(remnant intimal flap, flow in false lumen, size, and shape), and involvement of arch vessels. RESULTS: Perigraft sites were demonstrated on spin-echo axial images (9/11), and in no case was theredemonstrable hematoma or perigraft flow. Distal anastomotic sites were identifiable in 17 of 20 cases, and graftredundancy was noted in eight. Remnant false lumen distal to the graft vessel was present in all patients who hadundergone DeBakey type 1 aortic dissection(n=14). Flow in the false lumen was also demonstrated in all DeBakeytype 1 cases on spin-echo images and MR angiography. Remnant false lumen increased in size in six of 14 cases, andtended to show a concave margin to true lumen compared with preoperative imaging. In 8 of 9 patients whose archvessels had been preoperatively involved, intimal flaps in arch vessels remained. CONCLUSION: MR imaging is auseful tool for the postoperative assessment of patients who have undergone aortic dissection. In addition,remnant intimal flap, flow dynamics in false lumen, and involvement of arch vessels can be easily identified by MRangiography.

Evaluation of Acute Aortic Dissection by Use with Gadolinium Enhanced MR Angiogra p hy: Comparison withSpin-echo MR Image

PURPOSE: To compare the usefulness of Gadolinium-enhanced MR angiography(Gd-MRA) with spin-echo(SE) MRI forthe evalvation of acute aortic dissection. MATERIALS AND METHODS: During a recent one-year period weretrospectively reviewed the results of SE MRI and Gd-MRA in 14 patients (10 males, 4 females; mean age 57 years)with acute aortic dissection. DeBakey type I was found in six patients, DeBakey type II in one, and DeBakey typeIII in seven. MR techniques were as follows. First, multislice multiphase images were obtained in axial, coronaland oblique sagittal planes using SE T1WI(TR/TE/flip angle=600/14/90; acquisition time=25min), and images ofselected slices were obtained using breath-hold turbo SE T2WI(TR/TE/flip angle=800/76/160). Second, breath-holdGd-MRA imaging (3D-FISP; TR/TE/Flip angle=4.2/1.7/25; acquisition time=1min) was performed, with oblique sagittal(arch view) orientation. We compared 14 SE MRI images with nine thoracic and five abdominal Gd-MRA images,evalvating the presence and extent of intimal flap, entry and reentry tear, thrombus in false lumen (andcomparison to true lumen), the involvement of major branching vessels of the aortic arch, the origin of majorabdominal branching vessels, the presence of hemothorax and hemopericardium. RESULTS: Both SE MRI and Gd-MRA veryaccurately detected the extent of intimal flap, and false lumen status. For detecting the site of entry tear, andthe involvement of major branching vessels at the aortic arch, Gd-MRA(n=12) was more accurate than SE MRI(n=7).When used to image 20 vessels in five patients, Gd-MRA identified with perfect accuracy the origin of majorabdominal branching vessels; SE MRI, however, demonstrated only six of 20 vessels. SE MRI, however, was muchsuperior for the identification of complications such as hemothorax(n=9) and hemopericardium(n=2); in thisrespect, Gd-MRA failed completely. CONCLUSION: For the evaluation of patients with acute aortic dissection, Gd-MRAprovides information regarding site of entry tear and the involvement of major branching vessels very much fasterthan SE-MRI. In such cases, Gd-MRA can therefore be used for initial investigatory imaging.