Flat-panel volume CT: fundamental principles, technology, and applications.

Flat-panel volume computed tomography (CT) systems have an innovative design that allows coverage of a large volume per rotation, fluoroscopic and dynamic imaging, and high spatial resolution that permits visualization of complex human anatomy such as fine temporal bone structures and trabecular bone architecture. In simple terms, flat-panel volume CT scanners can be thought of as conventional multidetector CT scanners in which the detector rows have been replaced by an area detector. The flat-panel detector has wide z-axis coverage that enables imaging of entire organs in one axial acquisition. Its fluoroscopic and angiographic capabilities are useful for intraoperative and vascular applications. Furthermore, the high-volume coverage and continuous rotation of the detector may enable depiction of dynamic processes such as coronary blood flow and whole-brain perfusion. Other applications in which flat-panel volume CT may play a role include small-animal imaging, nondestructive testing in animal survival surgeries, and tissue-engineering experiments. Such versatility has led some to predict that flat-panel volume CT will gain importance in interventional and intraoperative applications, especially in specialties such as cardiac imaging, interventional neuroradiology, orthopedics, and otolaryngology. However, the contrast resolution of flat-panel volume CT is slightly inferior to that of multidetector CT, a higher radiation dose is needed to achieve a comparable signal-to-noise ratio, and a slower scintillator results in a longer scanning time.

Improved vessel morphology measurements in contrast-enhanced multi-detector computed tomography coronary angiography with non-linear post-processing.

Multi-detector computed tomography (MDCT) permits detection of coronary plaque. However, noise and blurring impair accuracy and precision of plaque measurements. The aim of the study was to evaluate MDCT post-processing based on non-linear image deblurring and edge-preserving noise suppression for measurements of plaque size. Contrast-enhanced MDCT coronary angiography was performed in four subjects (mean age 55 +/- 5 years, mean heart rate 54 +/- 5 bpm) using a 16-slice scanner (Siemens Sensation 16, collimation 16 x 0.75 mm, gantry rotation 420 ms, tube voltage 120 kV, tube current 550 mAs, 80 mL of contrast). Intravascular ultrasound (IVUS; 40 MHz probe) was performed in one vessel in each patient and served as a reference standard. MDCT vessel cross-sectional images (1 mm thickness) were created perpendicular to centerline and aligned with corresponding IVUS images. MDCT images were processed using a deblurring and edge-preserving noise suppression algorithm. Then, three independent blinded observers segmented lumen and outer vessel boundaries in each modality to obtain vessel cross-sectional area and wall area in the unprocessed MDCT cross-sections, post-processed MDCT cross-sections and corresponding IVUS. The wall area measurement difference for unprocessed and post-processed MDCT images relative to IVUS was 0.4 +/- 3.8 mm2 and -0.2 +/- 2.2 mm2 (p < 0.05), respectively. Similarly, Bland-Altman analysis of vessel cross-sectional area from unprocessed and post-processed MDCT images relative to IVUS showed a measurement difference of 1.0 +/- 4.4 and 0.6 +/- 4.8 mm2, respectively. In conclusion, MDCT permitted accurate in vivo measurement of wall area and vessel cross-sectional area as compared to IVUS. Post-processing to reduce blurring and noise reduced variability of wall area measurements and reduced measurement bias for both wall area and vessel cross-sectional area.

Analysis of left ventricular hemodynamics in physiological hyperspace.

Our laboratory has previously shown that it is possible to elucidate novel physiological relationships by analyzing the left ventricular pressure (P) contour in the phase [time derivative of P (dP/dt) vs. P] plane (Eucker SA, Lisauskas JB, Singh J, and Kovács SJ, J Appl Physiol 90: 2238-2244, 2001). To further characterize cardiac physiology, we introduce a method that combines P-volume (V) and phase plane-derived information in physiological hyperspace. From four-dimensional (P, V, dP/dt, time derivative of V) hyperspace, we consider three-dimensional embedding diagrams having dP/dt, P, and V as coordinate axes. Our method facilitates analysis of physiological function independent of inotropic state and permits assessment of P-V-based relationships in the phase plane and vice versa. To test feasibility, the method was applied to murine hemodynamic data. As predicted from first principles, the area of the P-V loop (ventricular external work) correlated closely (r = 0.97) with phase plane limit cycle area (external power). The P-V plane-derived linear (r = 0.99) end-systolic P-V relationship (maximum elastance) appeared linear in the phase plane (r = 0.85). We conclude that analysis of data in physiological hyperspace is generalizable: it facilitates quantitative characterization of ventricular systolic and diastolic function and can guide discovery of novel physiological relationships.

The left ventricular color M-mode Doppler flow propagation velocity V(p): in vivo comparison of alternative methods including physiologic implications.

Three alternative methods have been proposed for determining the "velocity of propagation" (V(p)) from color M-mode Doppler transmitral flow images. A quantitative intermethod comparison is performed by using a broad class of images encountered in clinical practice. V(p) for 13 subjects was measured by using each of the 3 methods and then statistically compared. Differences among the definitions of V(p) generated large differences in its numerical value when computed from the same image. Depending on the choice of method, the value of V(p) can vary by as much as 250%. Advantages and limitations of each method are discussed in the context of the physical meaning of V(p). Development of an optimal version of V(p) and consensus on how it should be defined merits further attention. This will require a multidisciplinary approach encompassing physiology, fluid dynamics, image processing, and mathematical modeling.

Histopathologic validation of the intravascular ultrasound diagnosis of calcified coronary artery nodules.

A calcified nodule is a type of potentially vulnerable plaque accounting for approximately 2% to 7% of coronary events. Because its intravascular ultrasound (IVUS) features have never been validated, the aim of this study was to assess the IVUS characteristics of calcified nodules in comparison to histopathology. IVUS was performed in 856 pathologic slices in 29 coronary arteries (11 left anterior descending, 5 left circumflex, and 13 right coronary arteries) in 18 autopsy hearts. Pathologic sections were analyzed every 2 mm; qualitative and quantitative findings of matched IVUS were analyzed. IVUS detected calcification in 285 frames; 17 (6.0%) were calcified nodules, and 268 (94.0%) were non-nodular calcium by histopathology. Two calcified nodules (11.8%) were solitary, and 15 (88.2%) were adjacent to non-nodular calcium. IVUS characteristics of calcified nodules were (1) a convex shape of the luminal surface (94.1% in calcified nodules vs 9.7% in non-nodular calcium, p <0.001), (2) a convex shape of the luminal side of calcium (100% vs 16.0%, p <0.001), (3) an irregular luminal surface (64.7% vs 11.6%, p <0.001), and (4) an irregular leading edge of calcium (88.2% vs 19.0%, p <0.001). Luminal area at the calcified nodule site was larger (6.2 ± 2.4 vs 4.3 ± 1.6 mm(2), p <0.001) and plaque burden less (57 ± 6% vs 68 ± 5%, p <0.001) than at the minimum luminal area site. In conclusion, calcified nodules have distinct IVUS features (irregular and convex luminal surface) permitting their prospective identification in vivo.

Topographic association of angioscopic yellow plaques with coronary atherosclerotic plaque: assessment with quantitative colorimetry in human coronary artery autopsy specimens.

Yellow plaques seen during coronary angioscopy are thought to be the surrogates for superficial intimal lipids in coronary plaque. Given diffuse and heterogeneous nature of atherosclerosis, yellow plaques in coronaries may be seen as several yellow spots on diffuse coronary plaque. We examined the topographic association of yellow plaques with coronary plaque. In 40 non-severely stenotic ex-vivo coronary segments (average length: 52.2 +/- 3.1 mm), yellow plaques were examined by angioscopy with quantitative colorimetry. The segments were cut perpendicular to the long axis of the vessel at 2 mm intervals, and 1045 slides with 5 microm thick tissue for whole segments were prepared. To construct the plaque surface, each tissue slice was considered to be representative of the adjacent 2 mm. The circumference of the lumen and the lumen border of plaque were measured in each slide, and the plaque surface region was constructed. Coronary plaque was in 37 (93%) of 40 segments, and consisted of a single mass [39.9 +/- 3.9 (0-100) mm, 311.3 +/- 47.4 (0.0-1336.2) mm2]. In 30 (75%) segments, multiple (2-9) yellow plaques were detected on a mass of coronary plaque. The number of yellow plaques correlated positively with coronary plaque surface area (r = 0.77, P < 0.0001). Yellow plaques in coronaries detected by angioscopy with quantitative colorimetry, some of them are associated with lipid cores underneath thin fibrous caps, may be used to assess the extent of coronary plaque. Further research using angioscopy could be of value to study the association of high-risk coronaries with acute coronary syndromes.

Detection of lipid core coronary plaques in autopsy specimens with a novel catheter-based near-infrared spectroscopy system.

OBJECTIVES: This study sought to assess agreement between an intravascular near-infrared spectroscopy (NIRS) system and histology in coronary autopsy specimens. BACKGROUND: Lipid core plaques cannot be detected by conventional tests, yet are suspected to be the cause of most acute coronary syndromes. Near-infrared spectroscopy is widely used to determine the chemical content of substances. A NIRS system has been developed and used successfully in 99 patients. METHODS: Scanning NIRS was performed through blood in 212 coronary segments from 84 autopsy hearts. One histologic section was analyzed for every 2 mm of artery. Lipid core plaque of interest (LCP) was defined as a lipid core >60 degrees in circumferential extent, >200-microm thick, with a mean fibrous cap thickness <450 microm. The first 33 hearts were used to develop the algorithm; the subsequent 51 validation hearts were used in a prospective, double-blind manner to evaluate the accuracy of NIRS in detecting LCP. A NIRS-derived lipid core burden index for an entire artery was also validated by comparison to histologic findings. RESULTS: The LCPs were present in 115 of 2,649 (4.3%) sections from the 51 validation hearts. The algorithm prospectively identified LCP with a receiver-operator characteristic area of 0.80 (95% confidence interval [CI]: 0.76 to 0.85). The lipid core burden index detected the presence or absence of any fibroatheroma with an area under the curve of 0.86 (95% CI: 0.81 to 0.91). A retrospective analysis of lipid core burden index conducted in extreme artery segments with either no or extensive fibroatheroma yielded an area under the curve of 0.96 (95% CI: 0.92 to 1.00), confirming the accuracy of spectroscopy in identifying plaques with markedly different lipid content under ideal circumstances. CONCLUSIONS: This novel catheter-based NIRS system accurately identified lipid core plaques through blood in a prospective study in coronary autopsy specimens. It is expected that this novel capability will be of assistance in the management of patients with coronary artery disease.

Arterial wall imaging: evaluation with 16-section multidetector CT in blood vessel phantoms and ex vivo coronary arteries.

PURPOSE: To evaluate the diagnostic performance of 16-section multidetector computed tomography (CT) for assessment of plaques in phantoms and ex vivo coronary arteries, with intravascular ultrasonography (US) and optical coherence tomography (OCT) as reference standards. MATERIALS AND METHODS: Research protocol was HIPAA compliant and approved by institutional review board, without informed consent required. Blood vessel and lesion composition phantoms and ex vivo coronary arteries were imaged with 16-section CT. Wall areas of phantoms and ex vivo coronary arteries were measured with multidetector CT and intravascular US. Sensitivity and specificity for lipid detection were determined in lesion composition phantoms. CT numbers of blood vessel wall were determined in ex vivo coronary arteries and compared with lesion classification results from OCT. Agreement in dimensional measurements was compared (paired t tests). CT numbers within blood vessel wall of CT cross sections classified as lipid rich, fibrous, and calcified at OCT were compared (Kruskal-Wallis tests). RESULTS: Mean blood vessel wall areas measured with CT and US in phantoms were 9.2 mm(2) +/- 1.8 (standard deviation) and 10.4 mm(2) +/- 3.4 (bias, -1.3 mm(2) +/- 3.1; P < .05), respectively. Mean blood vessel wall areas measured in ex vivo coronary arteries with CT and US were 10.9 mm(2) +/- 4.1 and 9.1 mm(2) +/- 3.1 (bias, 1.8 mm(2) +/- 3.0; P < .001), respectively. Sensitivity and specificity of 93% and 92%, respectively, for identification of lipid-rich lesions were observed in lesion composition phantoms. Mean CT numbers in blood vessel wall of ex vivo coronary arteries identified at OCT as predominantly lipid rich, fibrous, and calcified were 29 HU +/- 43, 101 HU +/- 21, and 135 HU +/- 199, respectively (P < .001). CONCLUSION: Determination of composition of individual plaques from attenuation values can be more challenging because of overlapping values for different tissue types.