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Biomedical subjects

C B Higgins

Publications and source records attributed to C B Higgins.

At least 91 records · Page 5Linked to original sources
PubMed1997

Quantification of coronary artery volume flow rate using fast velocity-encoded cine MR imaging.

OBJECTIVE: Breath-hold velocity-encoded cine (VENC) MR imaging has been proposed as a method for measuring coronary blood flow. However, most studies have measured velocity rather than volume flow rate in the coronary arteries. The purpose of this study was to measure volume flow rate in the coronary artery of dogs using high-speed gradients and to compare MR flow measurements with those obtained with a sonographic flowmeter. MATERIALS AND METHODS: Fast VENC MR images were obtained with a high-speed-gradient 1.5-T MR system in seven anesthetized dogs before and after administration of dipyridamole. Images were acquired on double oblique planes perpendicular to the left anterior descending arteries with a slice thickness of 5 mm, a field of view of 20 x 10 cm, a velocity window of +/- 1 m/sec, an average imaging time of 21 sec, a TR/TE of 11/5, and a temporal resolution of 44 msec. RESULTS: Coronary flow measured with VENC MR imaging correlated well with flow measured by the flowmeter (r = .95, slope = 0.97, n = 88). Interobserver variability in measuring coronary flow volume was 8%. CONCLUSION: Fast VENC MR imaging with high-speed gradients can provide accurate quantification of volume flow rate in coronary arteries.

Animals↗
PubMed1997

Evaluation of electron beam CT coronary angiography in healthy subjects.

OBJECTIVE: This study evaluated the performance characteristics of electrocardiographically triggered, contrast-enhanced electron beam CT (EBCT) in defining the coronary artery lumen in healthy subjects. SUBJECTS AND METHODS: The coronary arteries of 11 healthy young men (mean age, 24 years old) were evaluated by contrast-enhanced EBCT. Measured parameters included degree of luminal enhancement, intravascular contrast-to-noise ratio, apparent luminal diameter, and length of continuously visualized lumen (100-H threshold for diameter and length measurements). RESULTS: Aortic blood pool attenuation was 44 +/- 5 H (mean +/- SD) before and 278 +/- 35 H after IV injection of contrast material. Contrast-to-noise ratios ranged from a high of 10.0 +/- 2.6 in the proximal right coronary artery to a low of 3.2 +/- 2.7 in the distal left circumflex artery, decreasing from proximal to distal within each vessel. Apparent luminal diameters were as follows: left main coronary artery, 4.5 +/- 0.6 mm; left anterior descending artery, 3.7 +/- 0.5 mm; left circumflex artery, 2.9 +/- 0.6 mm; and right coronary artery, 3.5 +/- 0.5 mm. The mean lengths of visualized lumina were as follows: left main coronary artery, 10 +/- 4 mm; left anterior descending artery, 65 +/- 26 mm; left circumflex artery, 45 +/- 20 mm; and right coronary artery, 58 +/- 24 mm. CONCLUSION: EBCT angiography can reveal the lumen of long segments of the major coronary arteries.

Adult↗
PubMed1997

Assessment of early left ventricular remodeling in orthotopic heart transplant recipients with cine magnetic resonance imaging: potential mechanisms.

We performed short axis cine magnetic resonance imaging studies in 11 patients 2 months after they underwent orthotopic heart transplantation (OHT), and in 10 control subjects, to measure left ventricular (LV) volumes, mass, and end-systolic wall stress to assess ventricular remodeling after OHT. Although there were no significant differences in ventricular volumes and ejection fractions between heart transplant recipients and control subjects, heart transplant recipients had significantly higher LV mass (198 +/- 61 vs 132 +/- 27 gm, p = 0.001). As a consequence of myocardial hypertrophy, end-systolic wall stress was significantly reduced in heart transplant recipients compared with control subjects (34 +/- 16 vs 57 +/- 10 kdyne/cm2, p = 0.001). Moreover, heart transplant recipients had significantly reduced end-systolic wall stress/volume ratio when compared with control subjects (0.89 +/- 0.3 vs 1.26 +/- 0.3 kdyne/cm2/ml, p < 0.01), indicating an already reduced LV contractility 2 months after heart transplantation. Univariate regression analysis revealed a significant correlation between LV mass and averaged cyclosporine levels, but no correlation between LV mass and blood pressure, cold ischemic time, acute rejection, age, body mass, blood pressure, plasma catecholamine levels, or plasma renin activity. Magnetic resonance imaging demonstrates early LV remodeling after OHT with reduced myocardial contractility. Cyclosporine may be contributing to these changes.

Adult↗
PubMed1997

[Contribution of MRI in the evaluation of ischemic heart diseases].

The high spatial and temporal resolution of MRI provides accurate identification of left ventricular endocardial and epicardial contours. Cine-MRI allows reliable and reproducible measurements of end-systolic and end-diastolic volumes, ejection fraction and left ventricular mass. These measurements are not based on any geometrical hypothesis and so remain valid in presence of ventricular deformation as observed after myocardial infarctions. The value of cine-MRI has been demonstrated in ischaemic heart disease for the study of regional left ventricular function, by analysis of left ventricular segmental function and systolic thickening of the myocardial walls. Cine-MRI may also be performed during pharmacological stress. In coronary patients without ventricular dysfunction at rest, stress cine-MRI enables detection of segmental wall motion abnormalities or reduction of systolic thickening in potentially ischaemic territories. Cine-MRI may contribute to be study of myocardial viability. Regional myocardial perfusion may also be assessed using the rapid sequences of imaging and contrast agents opacifying the intravascular compartment. In coronary patient, underperfused regions may there by be detected. The most rapid imaging techniques enable visualisation of the proximal segments of the coronary arteries and the measurement of blood velocity in the coronary arteries and the calculation of coronary reserve. Simultaneous analysis under basal conditions and after pharmacological stress of global and segmental left ventricular function and of myocardial perfusion, associated with the possibility of imaging the proximal coronary arteries and of measuring the velocity of coronary flow, makes MRI a complete non-invasive method of evaluating patients with ischaemic heart disease.

Contrast Media↗
PubMed1996

Quantification of the extent of area at risk with fast contrast-enhanced magnetic resonance imaging in experimental coronary artery stenosis.

Fast magnetic resonance (MR) imaging techniques have the capability of demonstrating regions of ischemia caused by stenosis. The size of the potentially ischemic area determines the importance of the stenosis. The purpose of this study was to determine the relative values of relaxivity-enhancing and magnetic-susceptibility MR contrast media in detecting and sizing the area at risk in dogs. Eight dogs were subjected to critical left circumflex coronary artery (LCX) stenosis. Sixty sequential inversion-recovery- and driven-equilibrium-prepared fast gradient recalled echo images were acquired during bolus administration of 0.03 mmol/kg gadodiamide or 0.4 mmol/kg sprodiamide in basal and vasodilated (dipyridamole-stress) states. The size of the area at risk was measured and compared with that measured post mortem. In the basal state, gadodiamide and sprodiamide equivalently altered the signal intensities of nonischemic myocardium and the territory of stenosed coronary artery. Dipyridamole produced a significant increase in left anterior descending coronary artery flow with a decrease in LCX flow. The hypoperfused region was observed as a low-and high-signal intensity region after administration of gadodiamide and sprodiamide, respectively. The size of the hypoperfused region was slightly smaller with gadodiamide (37.4% +/- 2.8%) and sprodiamide (34.0% +/- 2.2%) than the true area at risk measured post mortem (41.8% +/- 2.2%; p < 0.05). Dipyridamole perfusion MR imaging with relaxivity or susceptibility contrast media is a noninvasive method to identify and quantify the area at risk in the territory of a stenotic coronary artery. Changes in myocardial signal intensity on fast gradient recalled echo images reflect the augmentation of flow and volume induced with dipyridamole and are consistent with the "steal phenomenon."

Animals↗
PubMed1996

Verapamil reduces the size of reperfused ischemically injured myocardium in hypertrophied rat hearts as assessed by magnetic resonance imaging.

Contrast-enhanced magnetic resonance (MR) imaging was used to detect and quantify the extent of myocardial injury after a brief coronary occlusion and reperfusion in response to verapamil treatment in a rat model of left ventricular hypertrophy (LVH). Two groups of rats were prepared by banding the abdominal aorta for 7 to 8 weeks to produce LVH. Group 1 (n = 13) received oral verapamil for 3 days, whereas group 2 (n = 13) received no therapy. Before MR examination was performed, each rat was subjected to 25 min of coronary artery occlusion followed by 1 hour of reperfusion. T1-weighted spin echo images were acquired before and after 0.3 mmol/kg gadoteridol was injected. Three images were acquired at contiguous levels of the LV and used to estimate the size of the myocardial injury. The size of the infarcted region was demarcated at postmortem examination by using triphenyltetrazolium chloride dye (TTC). Before contrast medium was administered, no significant difference in signal intensity was seen between nonischemic and reperfused ischemically injured myocardium. After gadoteridol was injected, a hyperintense zone indicative of myocardial injury was observed in 8 of 13 rats treated with verapamil and in all untreated animals. The size of the injury was significantly larger in untreated hearts than in hearts treated with verapamil as defined on MR images (25% +/- 5% vs 18% +/- 5%, p < 0.05) and TTC staining (12% +/- 4% and 4% +/- 1%, p < 0.05). Good correlation (r = 0.91) was found between the two measurements. No significant difference in the size of jeopardy area was seen between the two groups as (defined by blue dye infusion). In conclusion, contrast-enhanced MR imaging is a suitable technique to evaluate the effects of therapies applied to reduce myocardial injury. Verapamil can cause reduction in the extent of ischemic injury after reperfusion of hypertrophied myocardium.

Animals↗
PubMed1996

Assessment of hemodynamic effects of angiotensin-converting enzyme inhibitor therapy in chronic aortic regurgitation by using velocity-encoded cine magnetic resonance imaging.

Long-term treatment with angiotensin-converting enzyme (ACE) inhibitors has beneficial effects in patients with chronic aortic regurgitation by reducing left ventricular volumes and regurgitant fraction. Velocity-encoded cine magnetic resonance imaging can directly measure antegrade (forward stroke volume) and retrograde blood flow (regurgitant volume) in the ascending aorta. Velocity-encoded cine magnetic resonance imaging was used in 9 patients with moderate to severe aortic regurgitation (regurgitant fraction 49% +/- 17%) to measure regurgitant fraction, regurgitant volume, and forward stroke volume at baseline and 3 months after therapy with enalapril (mean dose 29 +/- 13 mg). Ten additional patients with aortic regurgitation without any drug therapy served as a control group. In the treatment group, systolic blood pressure slightly decreased from 132 +/- 20 mm Hg to 121 +/- 14 mm Hg (p = not significant), whereas diastolic blood pressure and heart rate (beats per minute) remained unchanged. Regurgitant fraction decreased in 6 patients (responders) from 49% +/- 19% to 39% +/- 20% (percentage change 24% +/- 14%, p = 0.002) and was unchanged in 3 patients (nonresponder, 49% +/- 19% vs 51% +/- 16%; p = not significant). In the responder group, forward stroke volume increased from 128 +/- 32 ml to 148 +/- 57 ml, whereas regurgitant volume remained unchanged (67 +/- 40 ml vs 65 +/- 51 ml). At baseline, the responder group had a significant higher total vascular resistance than the nonresponder group (998 +/- 538 dyne.sec.cm-5 vs 625 +/- 214 dyne.sec.cm-5; p < 0.05). With enalapril treatment, total vascular resistance in the responder group tended to decrease (891 +/- 576 dyne.sec.cm-5), but slightly increased in the nonresponder group (679 +/- 276 dyne.sec.cm-5). The control group showed no changes in regurgitant fraction, regurgitant volume, forward stroke volume, and total vascular resistance at follow-up.

Adult↗
PubMed1996

Magnetic resonance imaging in ischemic heart disease.

The clinical use of MR imaging in ischemic heart disease is still limited, although this is the major cardiac disease afflicting populations of many countries. However, with the recent development of faster MR techniques, MR imaging provides multiple capabilities for the evaluation of most aspects of ischemic heart disease. We described the potential application of MR imaging for identifying and quantifying morphologic and functional alterations caused by myocardial infarction and ischemia; the contribution of MR contrast media to improve tissue characterization and to identify ischemic myocardium; and the application of fast MR imaging techniques for assessing anatomy and blood flow in the native coronary arteries and bypass conduits. With continued development of these capabilities, MR imaging has the potential to be a comprehensive noninvasive imaging modality in ischemic heart disease.

Contrast Media↗
PubMed1996

Acute hemodynamic effects of recently developed monomer and dimer magnetic resonance imaging contrast media: a comparative study.

RATIONALE AND OBJECTIVES: We evaluated and compared the acute cardiovascular effects of equiosmolar doses of recently developed nonionic monomer and macrocyclic dimer magnetic resonance (MR) imaging contrast media with the clinically available ionic and nonionic MR contrast media. METHODS: Normotensive adult Sprague-Dawley rats were divided into six groups of seven rats per group. Group 1 received the nonionic monomer Gd-CMPA-BMPA (500 mmol/l solution); group 2 received the nonionic dimer Gd(2)2(O)DO3A (500 mmol/l solution); group 3 also received Gd(2)2(O)DO3A but at a higher concentration (1,000 mmol/l solution); group 4 received gadopentetate dimeglumine (500 mmol/l solution); and group 5 received gadodiamide (500 mmol/l solution). Each rat received a rapid (1-2 sec) bolus intravenous injection of 0.1, 0.25, and 0.5 mmol/kg of each contrast agent. Group 6 was used to test the peak effects of quiosmolar glucose solutions (500, 1,000, and 2,000 mOsm/kg water). Data were acquired at baseline, 20 sec (peak effect) after injection, and 1, 3, 5, and 10 min after injection. Peripheral (systolic, diastolic, and mean) pressure, central venous pressure, left ventricular (LV) pressure (peak systolic and end diastolic) pressure, first derivative of left ventricular pressure (+/-dP/dt), rate pressure product, and heart rate were measured. RESULTS: Bolus administration (0.1, 0.25, and 0.5 mmol/kg) of Gd-CMPA-BMPA and gadodiamide (500 mmol/l) had no significant effects on the monitored cardiovascular parameters. Bolus injection of 0.25 and 0.5 mmol/kg Gd(2)2(O)DO3A (500 and 1,000 mmol/l) and gadopentetate dimeglumine (500 mmol/l) caused transient cardiovascular depression, including decreased peripheral blood pressure, LV systolic pressure, peak positive and negative dP/dt, and rate pressure product, but an increased LV end diastolic pressure. These cardiovascular effects were slightly less profound than those produced by gadopentetate dimeglumine. CONCLUSION: Gd-CMPA-BMPA and gadodiamide have no adverse cardiovascular effects. Gd(2)2(O)DO3A and gadopentetate dimeglumine cause vasodilation and reduced cardiac performance. Therefore, presuming similar effects, if Gd(2)2(O)DO3A and gadopentetate dimeglumine are to be used at high doses for the MR quantification of blood volume or as a bolus for perfusion study, appropriate consideration should be given to possible adverse physiologic changes.

Animals↗
PubMed1996

[Magnetic resonance tomography in myocardial ischemia: state of the art].

Recent developments in MR imaging have opened up new avenues in the investigation of ischaemic heart disease. Conventional unenhanced spin-echo sequences have been used to detect and quantify myocardial infarction. Along with the technical advances aimed at reducing motion artifacts and imaging time, the advent of contrast media for MR imaging has further strengthened its diagnostic capacities. The applications of MR contrast media are increasing, and they are becoming more specific, to enable differentiation of occlusive and reperfused myocardial infarctions and to discriminate between reversible and irreversible myocardial injury. Previous studies have also indicated that dual administration of both relativity-based and susceptibility-based contrast media can be used to determine whether viable myocardium is present in the reperfused ischaemic area. Magnetic susceptibility MR contrast media have the potential to demonstrate a region of the ischaemically injured myocardium in which myocardial necrosis is present. A cornerstone in the MR assessment of ischaemic heart disease has been achieved with the advent of fast MR imaging techniques. Ultrafast gradient-recalled-echo sequences or echo-planar imaging allow to monitor the first passage of the contrast medium through the heart. With the aid of MR contrast media, these techniques may be useful in estimating regional myocardial perfusion and blood volume. Experimental and clinical perfusion studies indicate that perfusion-sensitive MR imaging, particularly in concert with coronary vasodilators, can detect compromised myocardium. Combining myocardial perfusion imaging with the anatomic and functional information provided by other MR imaging techniques such as cine and velocity-encoded sequences could make MR imaging a comprehensive noninvasive diagnostic tool for the assessment of ischaemic heart disease.

Animals↗
PubMed1996

Coronary flow reserve: noninvasive measurement in humans with breath-hold velocity-encoded cine MR imaging.

PURPOSE: To measure coronary vasodilator reserve with breath-hold velocity-encoded cine magnetic resonance (MR) imaging. MATERIALS AND METHODS: Eight healthy adult volunteers underwent 1.5-T MR imaging. Velocity-encoded cine images were acquired at seven to 13 temporal phases in 25 seconds, with k-space segmentation and view-sharing reconstruction (+/- 1 m/sec velocity-encoding value) (repetition time msec/echo time msec = 16/9). Flow velocity in the left anterior descending (LAD) artery was measured twice before and twice after administration of dipyridamole (0.56 mg per kilogram of body weight). RESULTS: Peak diastolic coronary flow velocity in the LAD artery was 14.8 cm/sec +/- 1.9 (mean +/- standard deviation) in the baseline state. It increased significantly (P< .01) to 46.3 cm/sec +/- 10.2 after dipyridamole administration, with an average coronary reserve of 3.14 +/- 0.59. Interstudy and interobserver reproducibilities for measurement of peak diastolic velocity were, respectively, 9.5% +/- 1.6 and 7.0% +/- .2.5 in the baseline state and 6.8% +/- 2.2 and 3.4% +/- 1.5 after dipyridamole administration. CONCLUSION: Breath-hold velocity-encoded cine MR imaging provided reproducible assessment of coronary flow reserve in humans.

Adult↗
PubMed1996

Heart disease: functional evaluation with MR imaging.

Diagnosis of cardiovascular disease requires precise assessment of both morphology and function. Nearly all aspects of cardiovascular function can be quantified with fast magnetic resonance (MR) imaging techniques. Conventional and breath-hold cine MR imaging can provide precise and highly reproducible measurements of global and regional function of the left and right ventricles. Velocity-encoded cine (VEC) MR imaging provides measurements of blood flow in the heart and great vessels. Contrast-prepared fast gradient-echo sequences can be used to monitor the first-pass dynamics of contrast media, thus defining selective regional myocardial perfusion. Recently, the feasibility of using breath-hold VEC MR imaging to measure flow velocity in native coronary arteries and coronary revascularization conduits has been shown. This will most likely provide a noninvasive method for testing coronary vasodilator reserve and may emerge as a new method for detecting asymptomatic coronary artery disease.

Coronary Circulation↗
PubMed1996

MR imaging of conotruncal abnormalities.

MR imaging has been shown to be accurate in the diagnosis and follow-up of congenital abnormalities of the heart and great vessels in infants and children [1-3]. Although echocardiology, in many cases, remains the primary imaging technique in congenital heart disease, MR imaging is a useful adjunct [1-3]. The advantages of MR imaging include a wide field of view and multiplanar capabilities [1-3]. Echocardiology is often suboptimal in evaluating the superior mediastinum because of the narrow imaging window [3]. This fact is especially true in patients after surgery and in older children. Therefore, MR imaging often plays a role in the evaluation of the great vessels.

Adolescent↗
PubMed1996

Very fast cardiac imaging.

With very fast MR imaging techniques, myocardial perfusion can be assessed by monitoring the changes of myocardial signal intensity over time following bolus injection of a contrast medium. Very fast MR imaging techniques also allow for freezing of cardiac motion that is important for coronary MR angiography and their high temporal resolution allow for coronary flow reserve measurements. In the current overview, basic principles and strategies of very fast cardiac MR imaging are presented. In the second part, applications of these fast sequences in the fields of myocardial perfusion, coronary MR angiography, and low measurements are presented.

Animals↗