Whole-body MR angiography in patients with peripheral arterial disease.
BACKGROUND
Ph.D. project performed at Copenhagen University Hospital Herlev in the period 2007-2010.


OBJECTIVE
To investigate whole-body magnetic resonance angiography (WB-MRA) as diagnostic method in patients with peripheral arterial disease (PAD).


BACKGROUND
Due to the systemic nature of atherosclerosis patients with PAD often have concomitant arterial stenoses outside the peripheral arteries. In this respect, it seems desirable to perform whole-body angiography. Currently, WB-MRA is the only imaging modality allowing assessment of the total arterial system (excluding the coronary arteries) in one examination without limiting factors like invasiveness or ionizing radiation.


METHODS
Four studies were performed (I-IV). Study I investigated the feasibility of performing WB-MRA in a 3T MRI system using body coil acquisition and a blood-pool contrast agent. Study II investigated the impact of a hybrid scan technique on the performance of 3T WB-MRA using body coil acquisition and an extracellular contrast agent. The aim of study III was to investigate if addition of infra-genicular steady-state MRA (SS-MRA) to first-pass imaging alone improves diagnostic performance in 3T WB-MRA. The last study (IV) was a questionnaire-based investigation of patient acceptance of WB-MRA compared to digital subtraction angiography (DSA). In all studies the inclusion criterium was referral to DSA due to PAD. Exclusion criteria were overweight exceeding the MRI system's limitations, inability to lie still due to rest pain, allergy to gadolinium-based contrast media, chronic renal insufficiency with an estimated glomerular filtration rate (eGFR) < 30 ml/min/1.73 m², dialysis, inability to obtain informed consent, and contraindications for MRI (pacemaker, claustrophobia etc.). In total, 57 patients were investigated in the technical oriented studies (I: n = 11, II: n = 26, and III: n = 20). Seventy-nine patients were included in study IV. DSA served as method of reference for calculation of WB-MRA sensitivity and specificity for detection of significant (> 50% luminal narrowing or occlusion) arterial stenoses.


RESULTS
The feasibility of body coil acquisition 3T WB-MRA using the blood-pool contrast agent gadofosveset trisodium was shown in study I. Overall sensitivity and specificity for detection of significant arterial stenoses with WB-MRA were 0.66/0.68 (observer 1/2) and 0.82/0.93, respectively. The low sensitivity was caused by poor sensitivity in the lower leg region. Study II showed that a hybrid scan protocol improves the performance of body coil acquisition 3T WB-MRA performed with the extracellular contrast agent gadoterate. Compared to a standard sequential WB-MRA protocol, the hybrid protocol resulted in statistically significant higher image quality scores, as well as lower venous contamination scores in the lower leg region. Overall sensitivities for detection of significant stenoses were 0.63/0.66 using the standard sequential WB-MRA protocol, and 0.75/0.70 using the hybrid WB-MRA protocol. Study III showed that addition of infra-genicular SS-MRA to first-pass imaging is an effective means of improving gadofosveset-enhanced WB-MRA. Combined analysis of steady-state and first-pass images showed infra-genicular sensitivitiy of 0.81, compared to 0.42 for first-pass imaging alone. In general, specificities for characterization of arterial stenoses with WB-MRA were high, with overall values ranging from 0.82 to 0.97 in studies I-III. Study IV showed that patient acceptance of WB-MRA was superior to that of DSA in patients with PAD, with the majority of patients (60%) preferring WB-MRA. Concomitant arterial stenoses outside the peripheral arteries were found in 28-32% of the investigated PAD patients.


CONCLUSIONS
Body coil acquisition 3T WB-MRA is technically feasible using both a blood-pool and a standard non-specific extracellular contrast agent. However, the method is limited by low sensitivities for arterial stenoses. Hybrid examination technique and use of steady-state MRA are methods of improving WB-MRA. Patient acceptance of WB-MRA is superior to that of DSA. The rationale of using WB-MRA as diagnostic method in PAD patients is shown by the high prevalence of concomitant arterial stenosis outside the peripheral arteries.
Department of Diagnostic Radiology, Copenhagen University Hospital Herlev, Denmark. ywnielsen@gmail.com
Yousef Jesper Wirenfeldt
YJ
Nielsen
D003287:Contrast Media / Q000737:chemistry; D006801:Humans; D018810:Magnetic Resonance Angiography; D010342:Patient Acceptance of Health Care; D058729:Peripheral Arterial Disease / Q000175:diagnosis*; D011237:Predictive Value of Tests; D051598:Whole Body Imaging
D003287:Contrast Media