Looking beyond the lumen does make all the difference.
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Aged↗
Biomedical subjects
Alan R Moody
Publications and source records attributed to Alan R Moody.
Magnetic resonance direct thrombus imaging in moderate carotid artery stenosis.
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Aged↗
In vivo identification of complicated upper thoracic aorta and arch vessel plaque by MR direct thrombus imaging in patients investigated for cerebrovascular disease.
OBJECTIVE: The objective of this article was to assess the feasibility of MR direct thrombus imaging (MRDTI) to evaluate the prevalence and location of complicated upper thoracic aortic and arch vessel plaque in patients referred for evaluation of cerebrovascular disease. SUBJECTS AND METHODS: Patients referred for investigation of cerebrovascular disease by MRI were enrolled. Reasons for referral included transient ischemic attack/amaurosis fugax, acute infarct, remote infarct, or asymptomatic carotid disease. Of the 348 patients initially scanned, 17 were excluded from the analysis. The final patient population included 331 patients (199 men, 132 women; mean age, 67.7 years). Patients were scanned using MRDTI, a 3D, T1-weighted, fat-suppressed spoiled gradient echo that exploits the T1 shortening effects of methemoglobin, directly visualizing hemorrhage/thrombus in the vessel wall, thus identifying complicated plaque. Complicated plaque was defined as a high signal within the atherosclerotic plaque at least twice the signal intensity of muscle. RESULTS: Forty-three of 331 patients (13%) had complicated upper thoracic aortic atherosclerotic disease, arch vessel atherosclerotic disease, or both. The upper thoracic aorta was involved in 36 of 43 patients (83.7%), and the left subclavian artery was involved in 14 of 43 patients (32.6%). Both the right subclavian artery and the brachiocephalic artery were involved in one of 43 patients (2.3%). Complicated carotid plaque was seen in 25 of 43 patients (58.1%). CONCLUSION: MRDTI can be applied in the detection of complicated plaque in the upper thoracic aorta and arch vessels. Complicated plaque was identified in 13% of the patient population. The upper thoracic aorta was the most common site involved. This technique could be useful for the screening of asymptomatic at-risk patients.
Adult↗
Iliac compression syndrome and recanalization of femoropopliteal and iliac venous thrombosis: a prospective study with magnetic resonance venography.
OBJECTIVES: Poor iliac vein recanalization has been associated with compression of the left common iliac vein by the right common iliac artery (RCIA/LCIV compression); however, this finding has been difficult to confirm. In a baseline study, RCIA/LCIV compression was detected with magnetic resonance imaging in patients with deep venous thrombosis. We compared recanalization of left femoropopliteal and iliac thrombosis with and without RCIA/LCIV compression. METHODS: This was a prospective blinded study carried out in a 1355-bed university hospital. Thirty-one patients were recruited from consecutive cohorts of patients with iliofemoral and femoropopliteal DVT who underwent direct thrombus magnetic resonance imaging, venous enhanced peak arterial magnetic resonance venography, and magnetic resonance arteriography as part of the baseline study relating RCIA/LCIV compression to extent of thrombosis. Magnetic resonance venography was performed 6 weeks, 6 months, and 1 year after diagnosis of deep venous thrombosis. Femoropopliteal and iliac venous segments that were occluded at diagnosis were classified as occluded, partially occluded, or patent on follow-up scans. RESULTS: At 6-week follow-up, recanalization of all segments was incomplete. At both 6-month and 1-year follow-up, recanalization of left iliac segments associated with RCIA/LCIV compression was poorer compared with recanalization of left iliac segments not associated with compression (6 of 6 occluded vs 1 of 6 occluded and 1 of 6 partially occluded at 6 months, P =.015; 6 of 6 occluded vs 5 of 5 patent at 1 year, P = .002). This was due to complete failure of recanalization of left common iliac veins associated with RCIA/LCIV compression in 6 of 6 cases. All other iliac and femoropopliteal segments including left external iliac veins associated with RCIA/LCIV compression had high rates of recanalization at both 6 months and 1 year. CONCLUSION: RCIA/LCIV compression is associated with persistent occlusion of the left common iliac vein. The recanalization rate for all other femoropopliteal and iliac segments was high.
Constriction, Pathologic↗
Re-evaluation of iliac compression syndrome using magnetic resonance imaging in patients with acute deep venous thromboses.
BACKGROUND: The majority of proximal deep venous thromboses (DVTs) are thought to have propagated as a contiguous column from the calf veins. However, several authors have proposed that ileofemoral DVT commonly originates in the left common iliac vein (LCIV) at a site of compression by the overlying right common iliac artery (RCIA/LCIV compression). This mechanism could explain both the left-sided predominance of ileofemoral DVT and the finding that ileofemoral DVT frequently occurs either in the absence of calf vein thrombosis (isolated ileofemoral DVT) or is not contiguous with calf vein thrombosis (noncontiguous ileofemoral DVT). This mechanism remains unconfirmed. OBJECTIVES: The purpose of this study was to detect RCIA/LCIV compression using multimodal magnetic resonance imaging in thrombosed and patent iliac veins, to determine whether RCIA/LCIV compression occurs more frequently in cases of left ileofemoral DVT than other types of DVT, and to determine if RCIA/LCIV compression is specifically associated with left isolated and noncontiguous ileofemoral DVT. PATIENTS AND METHODS: This prospective study conducted at the 1355-bed University Hospital included 18 patients with ileofemoral DVT, 23 with femoropopliteal DVT, 15 with isolated calf DVT recruited consecutively, and 28 control patients in whom DVT had been excluded. Interventions included magnetic resonance direct thrombus imaging (MRDTI), venous enhanced peak arterial magnetic resonance venography (VESPA) and magnetic resonance arteriography (MRA) within 48 hours of routine conventional venography (CV). RCIA/LCIV compression of patent LCIVs was assessed using VESPA and MRA; RCIA/LCIV compression of thrombosed LCIVs was assessed using MRDTI and MRA. The extent of calf and popliteal thrombosis was detected using CV; the extent of femoral and iliac thrombosis was detected using VESPA and MRDTI. RESULTS: RCIA/LCIV compression was more commonly detected in cases of left ileofemoral DVT (9/16 cases) than in cases of left femoropopliteal DVT (1/11 cases; P = .018), right femoropopliteal DVT (2/12 cases; P = .054), left isolated calf DVT (1/9 cases; P = .037), right isolated calf DVT (0/6 cases; P = .046) and control patients (4/28 cases; P = .006). RCIA/LCIV compression was more commonly detected in cases of left isolated ileofemoral DVT (6/6 cases; P = .005), and cases of left noncontiguous ileofemoral DVT (2/2 cases; P = .067) than in cases in which thrombosis was contiguous from the calf to the iliac veins (1/8 cases). CONCLUSION: RCIA/LCIV compression was strongly associated with left ileofemoral DVT and was specifically associated with cases that involve independent ileofemoral thrombosis.
Adult↗
Prevalence of complicated carotid atheroma as detected by magnetic resonance direct thrombus imaging in patients with suspected carotid artery stenosis and previous acute cerebral ischemia.
BACKGROUND: It is recognized that complicated plaque largely accounts for the morbidity and mortality from atherosclerosis. Ideally, investigation of symptomatic and asymptomatic patients would identify atheromatous plaques independently of stenosis. We have previously shown that a magnetic resonance direct thrombus imaging (MRDTI) technique demonstrates complicated atheroma as high signal within the carotid arterial wall. We used this technique to examine the prevalence of complicated carotid plaque in vivo in the ipsilateral arteries of recently symptomatic patients with suspected carotid artery stenosis and to compare this with their contralateral arteries and with those of healthy age- and sex-matched controls. METHODS AND RESULTS: The carotid arteries of 120 patients with suspected severe carotid artery stenosis and previous acute cerebral ischemia were imaged using MRDTI, as were 28 control arteries. High signal was not seen in any control artery. However, there was a 60% prevalence of high signal, suggestive of complicated plaque in the patients' ipsilateral arteries. The prevalence of high signal was significantly greater in the patients' ipsilateral vessels compared with the contralateral, asymptomatic side (60% versus 36%, chi2 P<0.001), particularly for vessels of only moderate stenosis. CONCLUSIONS: MRDTI high signal suggestive of complicated plaque is prevalent in the ipsilateral carotid arteries of patients with carotid stenosis and recent cerebral ischemic events. MRDTI has a potential role in identifying "at risk" plaque, studying atherogenesis and the effects of plaque-modifying strategies.
Brain Ischemia↗
Characterization of complicated carotid plaque with magnetic resonance direct thrombus imaging in patients with cerebral ischemia.
BACKGROUND: Thromboembolic disease secondary to complicated carotid atherosclerotic plaque is a major cause of cerebral ischemia. Clinical management relies on the detection of significant (>70%) carotid stenosis. A large proportion of patients suffer irreversible cerebral ischemia as a result of lesser degrees of stenosis. Diagnostic techniques that can identify nonstenotic high-risk plaque would therefore be beneficial. High-risk plaque is defined histologically if it contains hemorrhage/thrombus. Magnetic resonance direct thrombus imaging (MRDTI) is capable of detecting methemoglobin within intraplaque hemorrhage. We assessed this as a marker of complicated plaque and compared its accuracy with histological examination of surgical endarterectomy specimens. METHODS AND RESULTS: Sixty-three patients underwent successful MRDTI and endarterectomy with histological examination. Of these, 44 were histologically defined as complicated (type VI plaque). MRDTI demonstrated 3 false-positive and 7 false-negative results, giving a sensitivity and specificity of 84%, negative predictive value of 70%, and positive predictive value of 93%. The interobserver (kappa=0.75) and intraobserver (kappa=0.9) agreement for reading MRDTI scans was good. CONCLUSIONS: MRDTI of the carotid vessels in patients with cerebral ischemia is an accurate means of identifying histologically confirmed complicated plaque. The high contrast generated by short T1 species within the plaque allows for ease of interpretation, making this technique highly applicable in the research and clinical setting for the investigation of carotid atherosclerotic disease.
Aged↗
Deep venous thrombosis: diagnosis by using venous enhanced subtracted peak arterial MR venography versus conventional venography.
PURPOSE: To assess diagnostic accuracy and interobserver variability at venous enhanced subtracted peak arterial (VESPA) magnetic resonance (MR) venography compared with those at conventional venography for the diagnosis of femoral and iliac deep venous thrombosis (DVT). MATERIALS AND METHODS: A single anteroposterior maximum intensity projection (MIP) venogram of the femoral and iliac veins was constructed by using VESPA MR venography in 55 symptomatic patients suspected of having lower limb DVT. All patients also underwent conventional venography, results of which were used as the standard of reference. VESPA MR venograms were interpreted by two independent reviewers (reviewers A and B) who were unaware of other results. Sensitivity and specificity of VESPA MR venography for the diagnosis of thrombus in the femoral and iliac veins were calculated. Interobserver variability was calculated for these observations by using weighted kappa with equally spaced weights for positive, nondiagnostic, and negative studies. Nondiagnostic studies were reinterpreted separately by reviewer A on the basis of source data. RESULTS: Sensitivity of VESPA MR venography for the femoral veins (20 of 20) and iliac veins (seven of seven) was 100% for both reviewers. Specificity was 100% (39 of 39 for reviewer A, 40 of 40 for reviewer B) for the iliac veins and 97% (31 of 32) for the femoral veins for both reviewers. Segments in which the VESPA MR venograms were nondiagnostic were excluded from this analysis. Interobserver variability as calculated by using weighted kappa for positive, negative, and nondiagnostic studies was 0.85 for femoral veins and 0.97 for iliac veins. Interpretation of the source data led to correct diagnosis in six of six cases in which the VESPA MR venograms were nondiagnostic. CONCLUSION: VESPA MR venography yielded MIP venograms that were highly accurate for the diagnosis of DVT in femoral and iliac veins. Interpretation of the studies was also highly reproducible.
Adult↗
MR tagging of human lungs using hyperpolarized 3He gas.
PURPOSE: To evaluate the use of spin-tagging in conjunction with hyperpolarized gas imaging for monitoring lung ventilation and gas diffusion. METHODS AND MATERIALS: Images were taken at 0.15 T using single shot RARE, with hyperpolarized (3)He gas prepared by the metastability exchange technique. Sinusoidal modulation of the longitudinal magnetization (tag) was produced by two 90-degree rf pulses separated by a gradient pulse. The diffusion of (3)He gas in the lungs was measured by monitoring the decay of the tags. This study was conducted on a 25-year-old, male, healthy volunteer. RESULTS: Clear tags in hyperpolarized (3)He gas both in vivo and in vitro were generated. The relative movement of the lung compared to a static, partial breath-hold was measured following inspiration or expiration. The diffusion coefficient of (3)He in the lungs was found to be 0.02 +/- 0.005 cm(2)seconds(-1). CONCLUSION: The spin-tagging of hyperpolarized (3)He in the lungs is possible, and allows regional lung movements to be measured following inspiration and expiration. It also allows quantification of the diffusion of the (3)He gas.
Adult↗
MRI for the diagnosis of pulmonary embolism.
Pulmonary embolism (PE) is one of the most frequently encountered clinical emergencies. The diagnosis often involves multiple diagnostic tests, which need to be carried out rapidly to assist in the safe management of the patient. Recent strides in computed tomography (CT) have made big improvements in patient management and efficiency of diagnostic imaging. This review article describes the developments in magnetic resonance (MR) techniques for the diagnosis of acute PE. Techniques include MR angiography (MRA) and thrombus imaging for direct clot visualization, perfusion MR, and combined perfusion-ventilation MR. As will be demonstrated, some of these techniques are now entering the clinical arena, and it is anticipated that MR imaging (MRI) will have an increasing role in the initial diagnosis and follow-up of patients with acute PE.
Acute Disease↗
Separating arterial and venous components from 3D dynamic contrast-enhanced MRI studies using factor analysis.
Dynamic contrast-enhanced MRI has been used extensively for angiography but in order to generate separate arterial and venous images some form of postprocessing is required. This typically involves the subtraction of one image in a dynamic sequence from another in order to suppress unwanted signal; however, this also has the effect of decreasing the signal-to-noise ratio (SNR) of the image. In this study, factor analysis, a technique related to eigenimage filtering, is used to separate arterial and venous components from dynamic contrast-enhanced images of the legs acquired with a temporal resolution of 30 sec. The SNR of the venous and arterial images extracted from a series of 20 patients using conventional single subtraction, a double subtraction method, and factor analysis were compared. Results show that the use of factor analysis improved the SNR in the venous images by a factor of 2.3 compared with the use of simple subtraction. A subjective comparison of the maximum intensity projection images generated from the venous images was also carried out and showed a significant preference for those generated using factor analysis over those generated using other subtraction methods.
Contrast Media↗
Diagnosis of lower-limb deep venous thrombosis: a prospective blinded study of magnetic resonance direct thrombus imaging.
BACKGROUND: Current magnetic resonance techniques generate high signal from venous blood and show thrombi as filling defects. Magnetic resonance direct thrombus imaging (MRDTI) directly visualizes acute thrombus. OBJECTIVE: To determine the accuracy of MRDTI for diagnosis of acute symptomatic deep venous thrombosis (DVT) below and above the knee. DESIGN: Prospective, blinded study. SETTING: A 1355-bed university hospital. PATIENTS: 101 patients with suspected DVT who had had routine venography. Participants were recruited from a cohort of patients with suspected DVT. All patients with a positive venogram and one quarter of patients with a negative venogram were selected by using a random sequence. INTERVENTION: MRDTI was performed within 48 hours of venography and was interpreted by two reviewers. MEASUREMENTS: Diagnosis of DVT overall; isolated calf, femoropopliteal, and ileofemoral DVT; and thrombus in the calf, femoropopliteal, and iliac segments. RESULTS: The reports from two readers had sensitivities of 96% and 94% and specificities of 90% and 92% for diagnosis of DVT. Sensitivities were 92% and 83% for isolated calf DVT, 97% and 97% for femoropopliteal DVT, and 100% and 100% for ileofemoral DVT. Specificities were 94% and 96% for isolated calf DVT and 100% and 100% for both femoropopliteal and ileofemoral DVT. Similarly, sensitivity and specificity within each of the venous segments ranged from 91% to 100%. Interobserver variability measured by using a weighted kappa statistic ranged from 0.89 to 0.98 for these measures. CONCLUSION: Magnetic resonance direct thrombus imaging is an accurate noninvasive test for diagnosis of DVT, and its accuracy is maintained below the knee. Comparison of individual venous segments showed that results of MRDTI agreed strongly with findings on venography. Scanning was well tolerated, and interpretation was highly reproducible.
Adult↗
MR pulse sequences: what every radiologist wants to know but is afraid to ask.
The use of magnetic resonance (MR) imaging is growing exponentially, in part because of the excellent anatomic and pathologic detail provided by the modality and because of recent technologic advances that have led to faster acquisition times. Radiology residents now are introduced in their 1st year of training to the MR pulse sequences routinely used in clinical imaging, including various spin-echo, gradient-echo, inversion-recovery, echo-planar imaging, and MR angiographic sequences. However, to make optimal use of these techniques, radiologists also need a basic knowledge of the physics of MR imaging, including T1 recovery, T2 and T2* decay, repetition time, echo time, and chemical shift effects. In addition, an understanding of contrast weighting is very helpful to obtain better depiction of specific tissues for the diagnosis of various pathologic processes.
Humans↗