Magnetic resonance imaging of abdominal aortic grafts

The widespread use of abdominal aortic grafting procedures and increasing awareness of related complications suggests the need for a reliable and non-invasive diagnostic technique which will allow early detection of both occlusive and non-occlusive complications. Ultrasound is generally used with satisfactory results, but has several limitations, whereas MRI has shown great promise in the study of cardiovascular disease, being non-invasive, multiplanar and multiparametric. The present research aims to evaluate MRI in the follow-up of abdominal aortic grafts, attempting to define its significance as a screening procedure in non-selected patients. MRI is reliable in ascertaining the normality of the graft as well as the complications, these being partial or total thrombosis, pseudoaneurysms and perigraft collections. The data obtained are highly satisfactory and are almost always superior to those achieved with ultrasound and CT.     

Assessment of coronary artery bypass grafts patency with different magnetic resonance technologies.

OBJECTIVE: The aim of the study was to evaluate the diagnostic accuracy of different magnetic resonance (MR) sequences in the assessment of coronary artery bypass graft patency and the evaluation of distal anastomoses with a spin echo sequence (Haste). PATIENTS AND METHODS: Twenty-five patients were examined with all the three techniques and 185 patients with 481 distal anastomoses were examined with the Haste sequence at a 1.5 TMR scanner and coronary angiography. A two-dimensional T(2)-weigthed breath-hold half-Fourier acquisition single-shot turbo spin echo sequence (Haste), a Navigator sequence and a gadolinium-enhanced Fisp-3-D sequence were performed. All images were evaluated independently by a radiologist and cardiologist and compared to the conventional coronary angiography. The observers were blinded to the coronary angiography findings, but informed in regard to the surgical graft anastomosis. RESULTS: With the Haste sequence 80% of the distal anastomoses were recognized. The sensitivity and specificity for the evaluation of the distal anastomosis with the Haste sequence was 94% and 75%. The Navigator and the Fisp-3-D sequences showed a sensitivity of 74% and 94% and a specificity of 78% and 88%. CONCLUSION: The best results were achieved with the Haste sequence, a reliable assessment of graft patency of the distal anastomosis is possible. The best imaging of proximal IMA segments was possible with the Fisp-3-D sequence. Due to the low sensitivity and specificity, the use of the Navigator sequence was stopped in our center. Further improvements of the spatial resolution and the image quality are necessary to recommend this MR techniques for routine clinical use.     

Magnetic resonance angiography

MRA and MRI have become increasingly important diagnostic modalities in vascular surgery. The ability to obtain cross-sectional and angiographic images by these noninvasive and non-nephrotoxic modalities represents one of the most significant advances in vascular surgery over the past decade. We review the current status of MRI and MRA in vascular surgical practice.     

Magnetic resonance angiography and clinical evaluation of third nerve palsies and posterior communicating artery aneurysms

OBJECT: The authors conducted a study to determine the utility of the clinical profile and magnetic resonance (MR) angiography in evaluating patients with isolated third cranial nerve palsies or posterior communicating artery (PCoA) aneurysms. METHODS: Three-dimensional time-of-flight MR angiography was performed in a consecutive series of patients with isolated acute third cranial nerve palsy not due to a ruptured aneurysm and in patients with unruptured PCoA aneurysms. A neuroradiologist, masked to the identities of the patients, interpreted reformatted maximum intensity projection (MIP) and source images of the PCoAs and aneurysms. The investigators assessed clinical features of oculomotor nerve dysfunction and focal head pain. Cases involving cranial third nerve palsy without aneurysms were classified as Group 1 (no case entailed catheter-based angiography), and cases involving PCoA aneurysms seen on MR angiography (42 cases confirmed by catheter-based angiography) were classified as Group 2. The mean age of the 73 patients in Group 1 was 60.1 years and that of the 45 patients in Group 2 was 59.1 years (p = 0.37). The pattern and severity of oculomotor (p = 0.61) and lid (p = 0.83) dysfunction and pain frequency (p = 0.2) were similar for the 73 patients with vasculopathy in Group 1 and the 15 symptomatic patients in Group 2. Abnormal pupils were observed in 38% of the patients in Group 1 and 80% of those in Group 2 (p = 0.016). In cases of complete external third nerve palsy, nine of 22 in Group 1 and none of four in Group 2 had normal pupil function. For all patients, source imaging showed 206 PCoAs (85%) and MIP imaging demonstrated 120 PCoAs (49%). Of 48 aneurysms (three bilateral), MIP imaging showed 44 (92%) and source imaging showed 47 (98%). Only a 2-mm aneurysm seen on catheter-based angiography was missed by MR angiography. Symptomatic aneurysms were equal or greater than 4 mm in size. CONCLUSIONS: Only the presence of complete external third nerve palsy and normal pupil function allowed ischemia to be clinically distinguished from a PCoA aneurysm in a patient with isolated third nerve palsy and no subarachnoid hemorrhage. When source image MR angiography demonstrates normal findings, catheter-based angiography need not be performed in these patients, even if pupil function is abnormal.     

Detection of coronary artery bypass graft patency by contrast enhanced magnetic resonance angiography.

OBJECTIVE: The subject and purpose of the prospective study was to delineate coronary artery bypass graft (CABG) course and to determine patency of aortocoronary venous bypass grafts (ACVB) compared with internal mammary artery bypass grafts (IMA) in the early postoperative follow-up, by contrast enhanced magnetic resonance angiography (MRA). For control, patients were examined with X-ray angiography and spiral-computed tomography (CT). METHODS: Eighty-five patients (74 male/11 female) with a mean age of 63.7 years underwent MRA examination, applying contrast enhanced gradient-echo sequence after an average distance of 7 days from CABG surgery. A 1.5 Tesla magnetom vision (Siemens, Erlangen, Germany) with phased array coil technology was used. Overall, 247 bypass grafts (160 ACVB/87 IMA) were studied with a 3D (three dimensional) ultrashort TE gradient-echo sequence (TR/TE/a:5 ms/2 ms/40 degrees) with 512*512 matrix and 500 mm FoV in single breath-hold technique after Gd-DTPA bolus injection. CABGs were judged in three different parts, including the course of CABG and both anastomoses. CABGs were controlled by angiography and spiral-CT to examine sensitivity, specificity and efficiency of MRA examination. Additional measurement of bypass graft flow velocity of arterial and venous grafts was performed with 2D phase contrast technique in breath-hold technique with ECG triggering. RESULTS: One hundred and thirty-nine of 160 (86.9%) ACVB grafts and 83 of 87 (95.4%) IMA grafts could be visualized. Suspected occlusions of 10 CABGs were confirmed in 80% with a second modality. Five CABGs were false positive in MRA. MRA proved a high specificity (93.8%), sensitivity (89.9%) and efficiency (1.73), especially in detection of IMA to LAD and ACVB to LAD and RCA (Table 1). 3D maximum intensity projection (MIP) reconstruction was helpful in delineating CABG course and in several cases in detecting stenosis of coronary arteries. Results of flow velocity showed a significant higher mean systolic velocity in arterial bypasses than in venous grafts with a higher maximum velocity in systole than in diastole in both grafts. Bypass stenosis in distal anastomosis could not be verified with MRA and flow method. CONCLUSION: Contrast enhanced 3D ultrashort TE gradient-echo magnetic resonance angiography has the potential for being a reliable method for CABG visualization and CABG patency determination in the early postoperative period. MR flow measurement was not qualified for detection of a bypass stenosis.     

Magnetic resonance imaging in the evaluation of infantile torticollis

This retrospective study assessed the use of magnetic resonance imaging (MRI) in 58 infants with infantile torticollis. Eighteen patients had nonmuscular causes of torticollis (group 1); MRI identified lesions in 16 patients. Of 40 patients with a diagnosis of congenital muscular torticollis (group 2), 28 had a normal MRI. Five patients had asymmetry of the sternocleidomastoid without noticeable signal changes. Seven patients showd evidence of fibromatosis colli. Asymmetry of the posterolateral skull consistent with plagiocephaly was common. Magnetic resonance imaging did not alter treatment of group 2. Findings of compartment syndrome of sternocleidomastoid were inconsistent. Magnetic resonance imaging is not recommended for asymptomatic patients with infantile torticollis.     

Magnetic resonance imaging in the evaluation of prostate cancer

Summary Advantages of magnetic resonance imaging (MRI) in the study of prostatic disease include a precise anatomical display in multiple planes, superb contrast resolution, and differential physicochemical characteristics that are obtained without known toxicity. In practice, however, MRI has not been shown to differentiate consistently between normal and abnormal prostatic tissue. Although normal prostatic and periprostatic anatomy is clearly defined in T₁-weighted images, controversy persists as to the precise differential characteristics of inflammatory and neoplastic disease within the prostate. Thus, MRI is not presently adequate for prostate cancer screening. MRI has been shown to be superior to computerized axial tomography (CAT) for pelvic staging of prostate cancer; however, comparative studies involving other modalities with precise histologic confirmation are limited and the improvement reported is modest. There is some evidence that MRI may be helpful in the detection of prostate cancer metastatic to bone, but, again, information is limited. Substantial advances in MRI techniques such as optimal pulse sequencing, surface coils, and, possibly, paramagnetic contrast agents will be required to secure a role for MRI in prostate cancer evaluation.     

Magnetic resonance angiography in the preoperative evaluation of abdominal aortic aneurysms

Purpose: Contrast arteriography (CA) is a useful but invasive technique for the preoperative evaluation of patients with abdominal aortic aneurysms (AAA). To evaluate the use of magnetic resonance arteriography (MRA) as a preoperative study we prospectively studied 38 patients undergoing AAA repair.Methods: All patients underwent biplane CA and MRA with use of a gadolinium-enhanced technique. Radiographic studies were then independently evaluated by blinded radiologists for anatomic findings with CA used as the standard. Studies were then independently evaluated by blinded vascular surgeons, and a surgical plan was made.Results: With CA and intraoperative findings as the standards, MRA proved highly accurate in the determination of multiple key anatomic elements. The proximal extent of aneurysmal disease was correctly predicted in 87% (33/38) patients. Significant iliofemoral occlusive disease was identified with a sensitivity of 83% (5/6). Iliac or femoral aneurysms were detected with a sensitivity of 79% (22/28) and specificity of 86% (41/48). Significant renal artery stenosis was detected with a sensitivity of 71% (12/17) and a specificity of 99% (72/73). Accessory renal arteries were correctly identified in 71% (12/17). Surgeon evaluators correctly predicted the proximal cross-clamp site in 87% (33/38) of patients with use of MRA as compared with the actual operative conduct. Proximal anastomotic sites were correctly predicted in 95% (36/38) with MRA and 97% (37/38) with CA. Renal revascularization was predicted by MRA with a sensitivity of 91% (10/11) and specificity of 100% (65/65). The use of bifurcated aortic prostheses was correctly predicted by MRA in 75% (12/16), which was similar to that predicted by CA (81%, 13/16).Conclusions: MRA can provide preoperative anatomic information that is equivalent to CA for surgical planning. Because of favorable cost and patient safety considerations MRA will assume increasing importance in the preoperative evaluation of AAA. (J VASC SURG 1995;21:891-9.)     

Factors influencing patency of femoropopliteal artery bypass grafts

An analysis of 276 femoropopliteal bypass procedures performed in 264 patients at the Columbia-Presbyterian Medical Center over the past two decades showed a direct relationship of graft patency to preoperative popliteal artery runoff. Functional results were better than patency results. Sympathectomy and anticoagulation did not improve graft patency. The risk of amputation is outweighed by the benefits of restoration of blood flow to the ischemic extremity by a bypass procedure.     

Magnetic resonance angiography for preoperative evaluation of potential kidney donors

BACKGROUND: Careful evaluation of the renovascular anatomy for living kidney donors is essential to optimize donor and recipient outcomes. Arteriography has been the standard for delineating the renovascular anatomy. However, this procedure is invasive. Magnetic resonance angiography (MRA) is an attractive, noninvasive alternative. The aim of this study was to evaluate the accuracy of MRA in potential living kidney donors. METHODS: A retrospective comparison of the preoperative MRA results with the intraoperative anatomy was performed in 189 living kidney donors. RESULTS: MRA interpretations correctly identified the vascular anatomy of the donor kidneys in 173 donors (91.5%). In the remaining 16 patients (8.5%), the MRA interpretation was inaccurate. In 10 patients, the MRA reported fewer arteries than the number encountered during the donor operation, whereas in six patients MRA reported more arteries than what found during operation. In seven patients, MRA supplied additional important anatomical information, including kidney size disparity, the presence of nephrolithiasis, the presence of a renal cyst, and renal artery stenosis. All kidneys were successfully transplanted. The misinterpretation of the MRA did not adversely affect the recipient outcome. CONCLUSION: The noninvasive MRA evaluation of donor renovascular anatomy is an acceptable substitute for traditional angiography.     

Long-term patency of polytetrafluoroethylene vascular grafts in coronary artery surgery

Patients undergoing coronary revascularization may not have suitable autologous vessels for coronary artery grafting and therefore may need vascular prostheses. We present a case report of a patient undergoing coronary artery bypass with polytetrafluoroethylene vascular grafts. Follow-up has been 53 months, and the grafts remain patent.     

磁共振波谱成像(MRSI)应用于前列腺癌的评估

本文通过MRSI探讨前列腺病变组织中特定代谢产物的变化,评估对前列腺癌的诊断,定位和分期等方面的意义.     

Magnetic resonance imaging in the preoperative evaluation of cervical radiculopathy

Forty patients with cervical radiculopathy were examined preoperatively with magnetic resonance imaging (MRI). MRI was used alone in 27 (68%) of the 40 patients; the remainder also had computed tomography in conjunction with myelography. The primary criterion on MRI for a clinically significant lesion was asymmetrical narrowing of the subarachnoid space in the region of the nerve root. Surgical confirmation of the abnormality was obtained in all 40 cases. The operative findings were a herniated nucleus pulposus (32 of 40 patients), spondylosis (2 of 40 patients), or a combination of the two (6 of 40 patients). MRI identified a surgical lesion (herniated nucleus pulposus, spondylosis, or both) in 37 of the 40 (92%) patients. We think MRI is the only preoperative imaging examination necessary in most cases of cervical radiculopathy.     

Magnetic resonance angiography for the evaluation of vascular injury in knee dislocations

Knee dislocations can cause extensive soft tissue disruption including vascular insufficiency to the leg secondary to popliteal artery injury. Physical exam may miss vascular injury and possible late occlusion, but there is controversy regarding use of angiography to evaluate patients after dislocation. Magnetic resonance angiography (MRA) has been shown to be equally effective as angiography in evaluating vascular injury and to have fewer complications than angiography. Patients with knee dislocations routinely receive magnetic resonance imaging (MRI) to assess ligament integrity. The purpose of our study was to determine whether it may be prudent and convenient to obtain an MR angiogram at the same time as an MRI scan, with less morbidity and discomfort than with conventional angiography. Sixteen patients with frank and occult knee dislocations were prospectively evaluated over 2 years. After reduction, a physical exam was performed including ankle brachial index (ABI). With ABI < 0.90, emergent vascular surgery consult and angiogram was performed. Patients with ABI > 0.90 were observed for 3 days with serial physical exams, and MRI/MRA was performed as soon as possible. Sixteen dislocations were identified. Two of 16 (12.5%) had abnormal ABIs and received an angiogram and subsequent revascularization. Two had normal exams, but refused MRA. Twelve had normal exams and received MRI/MRA showing a normal popliteal artery with no adverse events. ABI had 100% sensitivity for vascular injury; however, there remains concern among treating surgeons about missing an occult injury such as an intimal tear. Because MRA has been shown to be as accurate and useful as angiography, we may be able to evaluate ligamentous and vascular injury simultaneously with less morbidity than that with conventional angiography.