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Biomedical subjects

A R Moody

Publications and source records attributed to A R Moody.

At least 19 recordsLinked to original sources
PubMed2003

Magnetic resonance direct thrombus imaging.

As blood clots it goes through predictable stages that reflect the oxygenation state of hemoglobin within the red cells. One of these stages results in the formation of methemoglobin. This substance acts an endogenous contrast agent when imaged using a T1-weighted magnetic resonance sequence (Magnetic Resonance Direct Thrombus Imaging, MRDTI) - appearing as high signal. MRDTI can therefore be used to detect subacute thrombosis. This technique has been applied in a number of clinical settings arising as a result of thrombosis. Deep vein thrombosis and pulmonary embolism are both readily detected using MRDTI, providing a single imaging modality for the detection of venous thromboembolic disease. The technique is also effective in the peripheral arterial tree. Furthermore, thrombosis within vessel wall atherosclerosis is a marker of vulnerable plaque likely to produce symptoms. The MRDTI technique has thus proved useful in identifying complicated plaque in the carotid arteries in the setting of transient and permanent cerebral ischemia. MRDTI therefore holds promise as a technique that is capable of detecting high risk vessel wall disease prior to significant or permanent end organ damage. Because of the non-invasive nature of magnetic resonance imaging (MRI), application of MRDTI in the research setting for the monitoring of therapeutic interventions in a wide number of settings within vascular disease is very appealing.

Female↗
PubMed2003

Differences in the diagnostic accuracy of acute stroke clinical subtypes defined by multimodal magnetic resonance imaging.

BACKGROUND: Despite its importance for acute stroke management, little is known about the underlying pathophysiology when patients with acute stroke are classified using clinical methods. OBJECTIVE: To examine the relation between the magnetic resonance defined stroke subtype and clinical stroke classifications using diffusion weighted imaging (DWI), perfusion weighted imaging (PWI), and angiographic magnetic resonance techniques. METHODS: Consecutive patients with clinical syndromes consistent with acute anterior circulation stroke were assessed clinically within six hours of onset and scanned as soon as possible using multimodal magnetic resonance imaging (MRI). Patients were classified clinically into total or partial anterior circulation syndromes using the Oxford classification, or according the severity of the National Institutes of Health stroke scale (NIHSS) (severe > 15; mild/moderate 15). There were 42 with partial anterior circulation syndromes (PACS) and 42 with total anterior circulation syndromes (TACS). Patients with TACS or severe stroke were more likely to have actually suffered a stroke (Fischer's exact test, p = 0.01), to have a correctly classified stroke (chi(2) 28.2, p < 0.01), to have persisting occlusion (chi(2) 30.6, p < 0.01), and to have a large DWI-PWI mismatch (chi(2) 17.1, p < 0.01). CONCLUSIONS: There is more inaccuracy in patients presenting with acute PACS or clinically mild to moderate anterior circulation stroke than in those with TACS or severe acute stroke syndromes. The latter appear more likely to be the targets for acute stroke interventions, as they include a significantly higher proportion of patients with persisting occlusion and diffusion/perfusion mismatch.

Acute Disease↗
PubMed2001

Extracting parametric images from dynamic contrast-enhanced MRI studies of the brain using factor analysis.

Factor analysis of dynamic studies (FADS) is a technique that allows structures with different temporal characteristics to be extracted from dynamic contrast enhanced studies without making any a priori assumptions about physiology. These dynamic structures may correspond to different tissue types or different organs or they may simply be a useful way of characterising the data. This paper describes a method of automatically extracting factor images and curves from contrast enhanced MRI studies of the brain. This method has been applied to 107 studies carried out on patients with acute stroke. The results show that FADS is able to extract factor curves correlated to arterial and venous signal intensity curves and that the corresponding factor images allow a distinction to be made between areas of the brain with normal and abnormal perfusion. The method is robust and can be applied routinely to dynamic studies of the brain. The constraints described are sufficiently general to be applicable to other dynamic MRI contrast enhanced studies where an increase in contrast concentration produces an increase in signal intensity.

Cerebrovascular Circulation↗
PubMed2000

Postirradiation aortic sarcoma demonstrated by magnetic resonance angiography.

This is the first ever reported case of a radiation-induced aortic sarcoma. This patient had symptoms and signs initially interpreted as a pulmonary embolus. The extent of the disease was demonstrated with magnetic resonance imaging and magnetic resonance angiography, in particular, allowing rapid surgical intervention.

Aortic Aneurysm, Thoracic↗
PubMed2000

Contrast-reduced imaging of tissue concentration and arterial level (CRITICAL) for assessment of cerebral hemodynamics in acute stroke by magnetic resonance.

RATIONALE AND OBJECTIVES: To compare cerebral perfusion data obtained by using a low-dose, T1-weighted MRI technique with radionuclide (single positron emission computed tomography [SPECT]) brain imaging and to assess the reproducibility of parametric MRI data (cerebral blood flow [CBF], cerebral blood volume [CBV], and time to peak [TTP]) by applying a previously described nuclear medicine technique to derive quantitative perfusion data. METHODS: Single-slice brain and neck images were rapidly acquired during the passage of a small (1/10th of normal dose) bolus of contrast. Parametric images were constructed from the MR data by extracting the bolus transit curve for the brain and the peak arterial input curve from the carotid vessels in the neck. These were compared with SPECT perfusion imaging. Twenty-four patients with acute stroke were studied with both techniques; 13 underwent repeated scanning to assess data reproducibility. RESULTS: Relative CBF data were comparable to SPECT data (r = 0.584, P = 0.01). Results were reproducible for relative CBF, CBV, and TTP. The arterial input function was significantly different on the second injection with an average difference of 73.5, suggesting that the signal-concentration relationship had lost linearity with increased contrast load. Absolute quantitative MRI data produced values in the expected range (CBF = 42.6 mL x 100 g(-1) x min(-1)). CONCLUSIONS: This technique allows estimation of CBF in the setting of acute stroke with quantitative values in the expected range. Repeated measurements in the same patients showed that this technique provides a reproducible measure of relative CBF, CBV, and TTP.

Brain↗
PubMed1999

Limitations of clinical diagnosis in acute stroke.

Trials in acute stroke have recruited on the basis of clinical diagnosis. Using MRI we have shown that clinical diagnosis is more limited than previously appreciated, thus trials may have been underpowered or confounded.

Clinical Trials as Topic↗
PubMed1998

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.

Aged↗
PubMed1998

Lower-limb deep venous thrombosis: direct MR imaging of the thrombus.

PURPOSE: To determine the feasibility of diagnosing deep venous thrombosis (DVT) with direct three-dimensional magnetic resonance (MR) imaging of the thrombus. MATERIALS AND METHODS: Eighteen patients with proved DVT at conventional venography were evaluated with a magnetization-prepared three-dimensional blood- and fat-suppressed MR imaging sequence. The presence and extent of thrombosis on the MR images were compared with the findings at conventional venography. RESULTS: At MR imaging, DVT was visualized in 17 of the 18 patients. MR imaging demonstrated greater proximal extent of the thrombosis in four patients, asymptomatic contralateral thrombosis in one, involvement of the deep femoral vein in five, and involvement of the superficial venous system in three. CONCLUSION: Direct MR imaging of clots appears capable of demonstrating venographically diagnosed DVT. This MR imaging technique is noninvasive, quick, and repeatable and allows a survey of the whole lower-limb venous system. Detection of thrombosis relies on the formation of methemoglobin, which appears to be sufficiently rapid to allow use of this technique in the clinical setting. Changes in the signal from clot over time may allow estimation of the age of the thrombus.

Feasibility Studies↗
PubMed1997

Dynamic T1 measurement using snapshot-FLASH MRI.

The application of an inversion-recovery snapshot FLASH (fast low-angled shot) imaging sequence to the dynamic measurement of monoexponential T1 relaxation was investigated. The effect of (a) a reduction in the overall sequence repetition time, and (b) an increase of the read-pulse flip angle, on the measurement of T1 was analyzed. The error in T1 introduced by these factors is calculated, and a fuller analysis that takes them into account is presented. Data from a phantom are used to confirm this analysis. The magnitude of the errors is illustrated by measuring myocardial T1 in patients with acute ischaemic heart disease during the injection of a bolus of the contrast medium gadobenate dimeglumine. Overall, there was a 10% difference between the T1 values when the approximate and exact solutions were used; this was statistically significant. However, the difference was on average 25% for patients with a high heart rate (because of the shorter sequence-repetition time) in areas of infarcted myocardium (because of the longer T1).

Contrast Media↗
PubMed1997

Magnetic resonance pulmonary angiography and direct imaging of embolus for the detection of pulmonary emboli.

RATIONALE AND OBJECTIVES: The authors developed a two-dimensional breathhold magnetic resonance (MR) technique for the direct imaging of pulmonary emboli. METHODS: In vitro MR imaging was performed to demonstrate the potential generation of clot-blood contrast by in vivo pulmonary embolism (PE). A two-dimensional magnetization prepared gradient-echo (turbo-FLASH) breathhold technique was designed to directly image intravascular emboli by the selective nulling of the blood signal. A turbo-FLASH pulmonary angiographic breathhold sequence was used to provide spatial localization of detected emboli. Thirteen patients with suspected PE were studied; 6 patients underwent conventional pulmonary angiography (CPA) and the remaining 7 had diagnoses based on findings from other studies. RESULTS: In vitro study of blood clot demonstrated an initial rise and then fall in T1 sufficient to generate clot-blood contrast after eight days of clot formation. All patients with CPA or alternative study evidence of PE were diagnosed as positive with direct embolus imaging MR. There were no false-positive diagnoses. Three additional emboli were detected using the MR technique compared with CPA. The MR pulmonary angiographic sequence provided a useful road map for localization of intravascular emboli but was less sensitive for PE detection than the embolus imaging technique. CONCLUSIONS: The direct imaging of PE is feasible using a simple two-dimensional breathhold technique.

Adult↗
PubMed1997

Comparison of transcranial color-coded sonography and magnetic resonance angiography in acute stroke.

BACKGROUND AND PURPOSE: We sought to compare the ability of transcranial color-coded Doppler sonography (TCCS) and magnetic resonance angiography (MRA) to identify circulatory changes that occur after acute stroke. METHODS: Forty-four patients with a clinical diagnosis of acute stroke were studied with both TCCS and MRA within 24 hours of stroke onset. The appearances of all vessels identified on MRA were divided into three categories: normal, attenuated, and absent vessels. The basal cerebral arteries were identified with the use of TCCS, and their velocities were measured with pulsed-wave Doppler. The side-to-side asymmetry was calculated and expressed as an asymmetry index. RESULTS: Five patients could not be studied with TCCS because of lack of a suitable acoustic window. An additional 4 patients were too restless to tolerate MRA scanning. Three patients had intracerebral hemorrhages, 2 patients had intracerebral gliomas, and the remaining 30 patients had cerebral infarctions. In the group of patients with acute cerebral infarction, TCCS identified 10 patients with normal asymmetry indices, 1 patient with an increased asymmetry index, 9 patients with decreased asymmetry indices, and 10 patients with occlusion of the symptomatic middle cerebral artery (MCA). MRA identified 8 normal angiograms, 6 patients had attenuated MCA branch vessels, 4 patients had MCA branch occlusions, 2 angiograms demonstrated MCA main stem attenuation, and 10 angiograms showed MCA occlusion. CONCLUSIONS: TCCS and MRA are both noninvasive techniques that can be used to study the acute stroke patient. They both yield information regarding the pathophysiology of acute stroke and may be useful techniques in deciding on therapeutic interventions. The findings agree closely with each other, and these techniques may be useful in the long-term follow-up of stroke patients.

Acute Disease↗
PubMed1995

Optimization of a breath-hold magnetic resonance gradient echo technique for the detection of interstitial lung disease.

RATIONALE AND OBJECTIVES: A rapid gradient echo technique was optimized to allow breath-held imaging of the lung parenchyma. The ability of this sequence to detect interstitial lung disease was then compared with high resolution computed tomography. METHODS: A Turbo-FLASH gradient echo sequence (repetition time [TR] 4.7, echo time [TE]2) was optimized using four volunteers. The parameters varied, including flip angle, inversion time, slice thickness, and number of measurements per unit time. The effect on signal to noise ratio of lung inflation and position within the lung were also studied. The optimized sequence was then compared with high resolution computed tomography in five patients being investigated for interstitial lung disease. RESULTS: Greatest signal was achieved using no inversion prepulse. This allowed up to six measurements, each with two acquisitions, during a single breath-hold. Optimum signal to noise ratio was achieved using a flip angle of 10 degrees with a 20-mm slice thickness, although a 10-mm slice was felt to be preferable for clinical use. Greatest signal to noise ratio was generated in the posterior aspect of the lung in full expiration. Comparison of the optimized magnetic resonance imaging technique with high resolution computed tomography showed no significant difference (P = 0.17) when assessing the proportion of diseased to normal lung. CONCLUSIONS: Using standard magnetic resonance software and hardware, it has been possible to use a breath-hold sequence that allows detection and quantification of interstitial lung disease.

Adult↗
PubMed1994

Digital sialography: imaging and intervention.

Digital subtraction imaging (DSI) has been widely used in angiography but less commonly applied to sialography. Over a 3-year period 109 patients referred for sialography, 42 males and 67 females with a mean age of 44 years (range 8-85 years), were examined using a digital subtraction imaging technique. 13 patients went on to have an interventional procedure, stone removal or duct dilatation. The role of DSI imaging in sialography and its use in facilitating interventional procedures on the salivary glands are discussed.

Adolescent↗