Biomedical subjects
Publications and source records attributed to Michael Hickman.
We came across an interesting case of calcific aortic stenosis in which severity was inaccurately assessed on two-dimensional and Doppler echocardiogram resulting in catheterization. Use of intravenous transpulmonary contrast agent enhanced the Doppler signal enabling better quantification of the transvalvular gradient. Use of contrast in such difficult to image patients is very useful in establishing a correct diagnosis.
OBJECTIVE: Cadaveric dissection is the gold standard for training physicians in various surgical specialties. However, limitations in acquiring and storing sufficient cadaveric material, recent pressures in training opportunities, and progress in digital image technology have led to advances in virtual or artificial visual means to augment surgical training. For training neurosurgeons, the appearance of reality is still crucial for learning anatomic structures and procedures. We developed a four-dimensional (including time) multilayer digital image reconstruction technology (MIGRT) that allows users to manipulate a "volumetric" set of photographic image data from exquisite cadaveric intracranial dissections and to navigate through stages of neurosurgical procedures as the dissection progresses. METHODS: A robotic microscope with two digital cameras was used to capture dissection images, usually in stereoscopic mode. A grid space was created to define positions at which images are captured. Images were acquired from identical angles at the same grid coordinates but at different stages of various dissections. RESULTS: Image data are reconstructed according to the sequence of acquisition into a multilayer image grid system by the MIGRT software. The single interactive, four-dimensional montage is viewable a on common computer platform. CONCLUSION: MIGRT uniquely focuses on capturing anatomic content that preserves natural appearances, including procedure, texture, and color, which is far superior and preferable to images and a reconstructed image environment based on artificial or animated concepts. MIGRT shows time-dependent changes in procedures, provides depth perception by stereoscopy or unique sequential motion, and allows simultaneous interactivity at each step of the procedure.
Myocardial uptake using (99m)Tc-sestamibi single photon emission computed tomography (SPECT) depends largely on myocardial microvascular volume. Myocardial contrast echocardiography (MCE) is a relatively new technique that detects not only microvascular volume but also blood flow. These differing mechanisms may affect the relative accuracies of MCE and SPECT for detecting myocardial viability (MV) early after acute myocardial infarction (AMI) and thrombolysis. Accordingly 56 patients underwent resting transthoracic echocardiography, low-power MCE and SPECT 7+/-2 days following first AMI and thrombolysis. Contractile reserve (CR) was assessed 3 months following revascularization. The sensitivity and specificity of MCE and SPECT were 83% and 78% (p=ns) and 78% and 45% (p<0.01) respectively. MCE was the only multivariate predictor of global recovery of function and CR (OR=3.5, p=0.01). The different physiological mechanisms employed by MCE and SPECT translate into different relative accuracies for the detection of MV.
OBJECTIVES: The purpose of this study was to compare myocardial contrast echocardiography (MCE) with single-photon emission computed tomography (SPECT) for the detection of significant coronary artery disease (CAD) in patients with symptoms suggestive of CAD. BACKGROUND: Single-photon emission computed tomography is a well-established method of assessing patients with CAD. Myocardial contrast echocardiography is a new technique allowing bedside assessment of myocardial perfusion. We hypothesized that MCE was comparable to SPECT in the assessment of patients with known or suspected CAD. METHODS: A total of 123 patients scheduled for coronary angiography underwent intermediate (mechanical index 0.5) triggered replenishment MCE and SPECT imaging at rest and after vasodilator stress. Coronary angiography was performed within four weeks of stress imaging. RESULTS: In total, 96 of 123 (78%) patients demonstrated CAD (stenosis >/=50%). There was no difference in the sensitivity of MCE compared with SPECT in the detection of CAD (84% vs. 82%; p = NS), and both demonstrated similar specificity (56% vs. 52%, respectively). In patients with multivessel disease, MCE and SPECT also demonstrated similar sensitivity (91% and 88%, respectively) for the detection of CAD. Agreement between MCE and SPECT for the presence or absence of CAD was 73%. CONCLUSIONS: Myocardial contrast echocardiography is comparable to SPECT in the detection of CAD not only on a patient basis but also in the localization of disease by vascular territory in a relatively high-risk population.
OBJECTIVES: We sought to assess the accuracy of hand-carried ultrasound (HCU) in the prediction of a normal study, and its cost-effectiveness in reducing the number of standard departmental echocardiograms (SDE) performed on hospital inpatients. METHODS: The setting was a district general hospital. Participants were 157 consecutive inpatients, mean age 68 (range: 18-97) years, 95 men (61%), referred for SDE. HCU was performed at the bedside as part of the clinical assessment. SDE was performed routinely. Main outcome measures were: (1) assessment of the accuracy of HCU in detection of a normal or abnormal study as determined by SDE; and (2) a cost-effectiveness analysis. RESULTS: Indications for echocardiography were: left ventricular (LV) function assessment, n = 101 (64.3%); valvular abnormalities, n = 11 (7%); arrhythmia, n = 4 (2.6%); miscellaneous, n = 10 (6.4%); and no reason stated, 31 (19.7%). The sensitivity, specificity, and positive and negative predictive values of HCU predicting a completely normal scan were 74%, 96%, 94%, and 81%, respectively, and of predicting normal LV function in requests specific for LV function assessment were 81%, 100%, 100%, and 77%, respectively. If either all inpatients or those with requests for LV function assessment underwent HCU initially, and only those with abnormal scans underwent further SDE, there would be a 29% and 22% reduction in departmental workload and a cost saving of pound sterling 23,000 and pound sterling 30,000, respectively. CONCLUSION: HCU is an accurate method of identifying patients with normal hearts as determined by SDE. Its routine use is cost-effective and can significantly reduce the number of SDE that need be performed.
Left atrial (LA) volume is a load-independent marker of left ventricular diastolic function. To determine the value of LA volume to predict mortality in patients with ischemic cardiomyopathy, clinical and echocardiographic variables, including Doppler parameters, were evaluated in 109 patients with ischemic cardiomyopathy. LA volume was the only independent predictor of mortality (hazard ratio 1.03, 95% confidence interval 1.001 to 1.057, p = 0.03).
Thirty-five patients underwent quantitative low-power myocardial contrast echocardiography to evaluate the severity of left anterior descending coronary artery stenosis. Coronary flow reserve and myocardial blood flow were able to accurately differentiate among angiographically derived grades of coronary stenosis.
Left ventricular (LV) hypertrophy (LVH) confers increased cardiovascular risk on patients with hypertension. Echocardiography using new hand-held devices might allow community-based cost-effective screening for LVH in a targeted hypertensive population. Thus, the aim of this study was to test the validity of hand-held ultrasound devices to screen for LVH in the community. Accordingly, 189 patients with hypertension attending a community-based heart failure screening program underwent echocardiography by both hand-held and standard devices by an experienced echocardiographer. LVH was defined as LV mass index >/=134 g.m(-2) for men and >/=110 g.m(-2) for women using the Devereux-modified American Society of Echocardiography cube equation. No significant differences were noted between the 2 devices in the measurement of LV wall thickness or LV mass index. Agreement for estimation of LVH between the 2 devices was 86% (kappa = 0.63). The sensitivity, specificity, and positive and negative predictive values of the hand-held device for predicting LVH were 72%, 91%, 73%, and 90%, respectively. Thus, hand-held echocardiography devices accurately assessed LVH and may be used for community-based screening for LVH in targeted patients with hypertension.
BACKGROUND: We investigated whether the extent of residual myocardial viability demonstrated by myocardial contrast echocardiography (MCE) predicts the degree of left ventricular (LV) remodelling after acute myocardial infarction as assessed by cardiovascular magnetic resonance. METHODS: Accordingly, 25 patients underwent MCE 5 to 7 days after acute myocardial infarction followed by cardiovascular magnetic resonance assessment of LV end-diastolic volume, LV end-systolic volume, and LV ejection fraction. A contrast perfusion index was calculated within the infarct-related territory. RESULTS: LV end-diastolic and end-systolic volumes were significantly smaller (138 +/- 38 vs 188 +/- 43 mL, P =.008, and 86 +/- 35 vs 119 +/- 49 mL, P =.01, respectively) and LV ejection fraction was significantly higher (52 +/- 5.4 vs 31.5 +/- 3.2%, P> =.02) in patients showing good myocardial viability (contrast perfusion index </= 1.5) compared with those without viability. MCE was the only multivariate predictor of LV volumes and LV ejection fraction at 2 weeks and 6 months. CONCLUSIONS: The extent of residual myocardial viability as demonstrated by MCE predicts the degree of LV remodelling after acute myocardial infarction.
OBJECT: The aim of this study was to acquire intraoperative images during neurosurgical procedures for later reconstruction into a stereoscopic image system (QuickTime Virtual Reality [QTVR]) that would improve visualization of complex neurosurgical procedures. METHODS: A robotic microscope and digital cameras were used to acquire left and right image pairs during cranial surgery; a grid system facilitated image acquisition with the microscope. The surgeon determined a field of interest and a target or pivot point for image acquisition. Images were processed with commercially available software and hardware. Two-dimensional (2D) or interlaced left and right 2D images were reconstructed into a standard or stereoscopic QTVR format. Standard QTVR images were produced if stereoscopy was not needed. Intraoperative image sequences of regions of interest were captured in six patients. Relatively wide and deep dissections afford an opportunity for excellent QTVR production. Narrow or restricted surgical corridors can be reconstructed into the stereoscopic QTVR mode by using a keyhole mode of image acquisition. The stereoscopic effect is unimpressive with shallow or cortical surface dissections, which can be reconstructed into standard QTVR images. CONCLUSIONS: The QTVR system depicts multiple views of the same anatomy from different angles. By tilting, panning, or rotating the reconstructed images, the user can view a virtual three-dimensional tour of a neurosurgical dissection, with images acquired intraoperatively. The stereoscopic QTVR format provides depth to the montage. The system recreates the dissection environment almost completely and provides a superior anatomical frame of reference compared with the images captured by still or video photography in the operating room.