Biomedical subjects

S Molloi

Publications and source records attributed to S Molloi.

24 records · Page 2Linked to original sources

PubMed1994

Quantitation of in vitro coronary artery calcium using ultrafast computed tomography.

Ultrafast computed tomography (UFCT) has the potential to quantify coronary hydroxyapatite (HAP). However, no definitive studies validating this technique are available. We constructed a human chest phantom model with coronary arteries represented by cylindrical holes containing: (1) calcium chloride solutions, (2) a block of HAP immersed in paraffin (without partial volume effect), and (3) HAP granules embedded in a gelatin matrix (with partial volume effect). We scanned this model to determine the relationship between measured CT number per voxel and density of the calcium per voxel. The relationships between CT number and concentration of calcium chloride was linear (r = 0.992 to 0.999). Using a commercially available standard bone mineral phantom, we were able to estimate the concentration of HAP to an accuracy from 94 to 97% when partial volume effects were absent. However, when partial volume effects were present, two methods of estimating HAP produced significant errors (1 to 384%, and 17 to 52%). We conclude that significant partial voluming errors degrade the accuracy of HAP quantitation and that further evaluation and corrections are needed before such quantitation is clinically applied.

Calcium Chloride↗

PubMed1994

Accuracy of quantifying coronary hydroxyapatite with electron beam tomography.

RATIONALE AND OBJECTIVES: The electron beam tomography coronary calcium score continues to be used without experimental validation. To determine its accuracy, a series of experiments was performed. METHODS: A chest phantom model was constructed with coronary arteries represented by cylindrical holes containing hydroxyapatite granules embedded in a gelatin matrix to simulate coronary arteries. Experiments were performed to determine the relationship between the mass of hydroxyapatite in each of these arteries, the coronary calcium score currently used in coronary screening, and an alternative method of estimating mass from the images. The model was scanned with equal amounts of hydroxyapatite in each artery: 1) when the cylindrical heart was rotated 36 degrees 10 times between scans, and 2) when the particle diameters varied from 0.1 mm to 4 mm. The scores were calculated, and a subtraction algorithm was applied to estimate the exact mass of hydroxyapatite in each artery. RESULTS: The hydroxyapatite scores varied by 42% with position and by 1.54 x 10(6)% with particle diameter. The estimated masses from the subtraction algorithm were more stable with position and particle size, with maximum percent errors of 10% and 14% for position and particle size, respectively. CONCLUSIONS: These results suggest that the coronary calcium score is invalid, and that more precise and clinically relevant methods, such as the arterial summation method, should be rigorously tested in clinical studies.

Algorithms↗

PubMed1992

Radiographically detectable calcium and atherosclerosis: the connection and its exploitation.

The early detection of coronary atherosclerosis may be impossible if we continue to depend on its pathophysiologic effects (ischemia) for our screening tests. Insoluble crystalline calcium phosphate, which is ubiquitous in our inorganic and biologic worlds, precipitates relatively early in atherosclerotic lesions. Since coronary calcification is specific for atherosclerosis and since calcium is a strong radiation absorber in the X-ray frequency range, sensitive radiographic techniques such as dual-energy subtraction fluoroscopy and ultrafast computed tomography hold promise as screening tests for this disease.

Calcinosis↗

PubMed1989

Whole body and regional retention of Tc-99m-labeled diphosphonates with a whole-body counter: a study with normal males.

A collimated whole-body counter was used to measure the retention and distribution of radioactivity along the longitudinal axis of the body at several times during the 24 hours after the intravenous injection of 50 microCi of Tc-99m-diphosphonates. Whole-body retention (WBR) was measured together with regional uptakes in the following four areas: head, chest, bladder, and legs using two structurally related Tc-99m-diphosphonate skeletal imaging agents: 1-hydroxyethylidene diphosphonate (HEDP) and methylene diphosphonate (MDP). The average 24 hour WBR values in young males, reflecting skeletal uptake of these tracers, were 17.7 +/- 2.2% (n = 20) and 31.0 +/- 2.4% (n = 3), respectively. A model of skeletal clearance was developed using the sum of two exponentials. In normal volunteers the initial rapid clearance phase of both tracers had a half-time of about 1 hour, whereas the slower second phase clearance had a half-time of 22 hours with HEDP and 44 hours with MDP. The WBR is usually calculated for the entire body only at 24 hours, but with the improved spatial resolution of a collimated whole-body counter, regional measurements could potentially be done over shorter periods (6-8 hours) in order to simplify the procedure.

Bone Diseases↗

PubMedDate not supplied

Quantification of coronary arterial calcium by dual energy digital subtraction fluoroscopy.

Clinical studies of the heart with fluoroscopy have shown that fluoroscopic visualization of calcium in the coronary arteries is strongly associated with coronary artery disease. However, fluoroscopic detection is limited by its low sensitivity, which is partly due to the interfering background tissue structures and image quantum noise. Moreover, quantification of the absolute amount of calcium in an arterial segment has not been possible. A real-time dual-energy subtraction technique has been investigated as a possible solution to the above problem. In this energy subtraction technique, the kVp and filtration are switched at 30 Hz. In order to assess the potential utility of this videodensitometric technique to quantitate coronary artery calcium, arterial phantoms and excised segments of diseased human arteries were imaged. The low- and high-energy images were corrected for scatter and veiling glare before subtraction. Calcium measurements were made using the tissue-suppressed energy-subtracted images. The estimated calcium phosphate and ashed weights of the calcified arterial segments (N = 20) were highly correlated (slope = 1.04, Intercept = -0.33 mg, r = 0.92).

Calcium↗

PubMedDate not supplied

Absolute volumetric blood flow measurements using dual-energy digital subtraction angiography.

In recent years, as a solution to the well-documented problems associated with visual interpretation of coronary arteriograms, more physiologic means of assessing coronary artery stenosis are being investigated. Absolute arterial blood flow assessed as a function of time can be a valuable aid in the analysis of functional significance of arterial lesions and obstructions. An absolute volumetric blood flow measurement technique using a motion immune dual-energy subtraction technique is being investigated, where the kVp and filtration are switched at 30 Hz. The low- and high-energy images are corrected for scatter and veiling glare before subtraction. In this technique, the absolute arterial blood flow is calculated by combining the videodensitometric analysis of spatial and temporal aspects concerning the contrast propagation through the arterial bed using tissue suppressed energy subtracted images. The blood flow measurement technique was validated using a pulsatile pump and a flow chamber imaged over a Humanoid chest phantom. A 20-MHz Doppler flow probe was used to validate the measurement of phasic volumetric blood flow. The measured (M) and known (K) mean blood flow for the entrance vessel technique and the videodensitometric calibration technique were related by M = 1.14K - 0.12 ml/s (r2 = 0.98) and M = 1.12K - 0.23 ml/s (r2 = 0.90), respectively. The results indicate that phasic volumetric blood flow can be measured using a CCD camera in conjunction with real time dual-energy subtraction.

Angiography, Digital Subtraction↗