Quantification of Obstructive and Nonobstructive Coronary Lesions by 64-Slice Computed Tomography: A Comparative Study With Quantitative Coronary Angiography and Intravascular Ultrasound

X-ray computed tomography (CT) is a well-established tissue imaging technique employed in a variety of research and clinical settings.1 Specifically, CT is a non-invasive clinical diagnostic tool that allows for 3D visual reconstruction and segmentation of tissues of interest. High resolution CT systems can be used to perform non-destructive 3D imaging of a variety of tissue types and organ systems, such as: the gastrointestinal tract, cardiovascular system, renal tract, liver, lungs, bone, cartilage, tumorous tissue, etc. CT is one of the most prevalent diagnostic tools in terms of frequency-of-use and hospital availability.2 The use of CT is on the rise and the number of clinical CT scanners in operation worldwide is estimated at over 45,000.1b Today, over 70 million clinical CT scans are performed yearly in the U.S. alone. For a recent detailed analysis of the use of clinical CT imaging and data regarding the number of regular and contrast-enhanced CT scans performed annually in the U.S. we refer the reader to the “Nationwide Evaluation of X-ray Trends” survey published by the Conference for Radiation Control Program Directors (CRCPD).3

The idea of using tomography (Greek: tomos = slice, graphein = draw) as a diagnostic tool in medicine was adopted soon after the discovery of X-rays by W. C. Roentgen in 1895. However, several more decades passed before the technology advanced sufficiently to bring those ideas to fruition. The first successful CT imaging device was built in 1972 by G. N. Hounsfield, at Electric and Musical Industries Ltd. In 1979, G. N. Hounsfield and South African physicist A. M. Cormack shared a Nobel Prize in medicine for their contributions to the field of X-ray CT imaging and diagnostics.4

X-rays are a form of electromagnetic radiation with wavelengths roughly between 0.01 nm and 10 nm. Traditionally, X-rays are generated by a vacuum tube using high voltage to accelerate electrons from a cathode to a (usually) tungsten-alloy anode. In the process, the accelerated electrons release electromagnetic radiation in the form of X-rays and the maximum energy of the radiation is limited by the energy of the incident electron. Operating voltages of modern clinical CT scanners differ among instrument models and manufacturers, but generally fall between 80 kVp to 150 kVp.

As a rule, materials possessing higher density (ρ) or high atomic number (Z) tend to better absorb X-rays. The relationship is best expressed in the formula for X-ray absorption coefficient (μ): 


μ≈ρZ4AE3

(1)


where “A” is the atomic mass and “E” is the X-ray energy. The strong relationship between absorption and atomic number is of significant importance in clinical applications. The Z4 factor allows for contrast levels of several orders of magnitude between different tissues and types of contrast agents.

When an incident X-ray has energy equal or slightly greater than the binding energy of the K-shell electron of the atom, a large sudden increase in absorption coefficient is observed. This energy value is known as absorption edge (k), and the k value increases with atomic number of the element. Consequently, X-ray attenuating contrast media containing atoms of high atomic number (most commonly iodine or barium), are frequently used in clinical settings to obtain images of soft tissues. To generate images with the highest contrast to the surrounding tissue, the energy of the X-ray source can be adjusted to closely match the absorption edge value (k) of the relevant imaging-agent atoms (i.e., iodine, barium, gold, etc.). Thus, it is also possible to do selective X-ray imaging and to differentiate between attenuating materials by fine tuning the energy source to the appropriate absorption edge value.

A CT image is obtained by rotating an X-ray source around an object, with a detector positioned directly opposite the radiation source. Alternatively, in many preclinical CT scanners the object sometimes is rotated around its own axis. Such preclinical scanners are often being used for small animal in vivo imaging. Generally, X-ray scans are taken at small angular increments during rotation around the object over 360°. A series of attenuation profiles or projections is thus obtained. The projections are then processed mathematically to create a 3D rendition of the scanned object. An in depth description of the engineering principles underlying modern CT imaging instruments is beyond the scope of this manuscript, and the reader is referred to other published works.1c,5

A diagnostic imaging method related to CT is X-ray fluoroscopy. Fluoroscopy allows for the acquisition of real-time, continuous images of the internal organs. Like in CT, imaging agents are often used in fluoroscopy for better contrast resolution. Small iodinated agents are commonly injected into blood vessels for use in fluoroscopic angiography, allowing for the evaluation of blood flow and visualization of the vasculature system, while barium contrast media are introduced orally or with an enema to investigate the anatomy (and pathology) of the gastrointestinal tract.

The introduction of magnetic resonance imaging (MRI) resulted in a loss of interest and reduction in CT contrast agent development throughout the 1980s. However, advances in computer technology, and the introduction and widespread adoption of spiral-CT in the mid-1990s have sparked a revival of interest in CT imaging and CT contrast media. Current clinical CT scanners are capable of acquiring high resolution 3D isotropic images of the body within several minutes. CT imaging today is less time consuming, less expensive, and more readily available than other medical imaging technologies such as MRI and positron emission tomography (PET). In the last several years, the emergence of novel technologies such as dual-source CT, and multi-detector CT has advanced the field of CT imaging even further. As a comparison to X-ray imaging diagnostic methods, PET imaging employs gamma-ray emitting radioactive nuclei “tracers” as contrast agents while MRI takes advantage of nuclear magnetic resonance principles by applying high magnetic fields to align magnetization of certain atomic nuclei. In contrast to CT and PET imaging, MRI uses no ionizing radiation and it is therefore often deemed safer than the other two.

X-ray-Computed Tomography Contrast Agents

SCCT guidelines for the interpretation and reporting of coronary CT angiography: a report of the Society of Cardiovascular Computed Tomography Guidelines Committee.

https://ccme.osu.edu/RSSeriesBrochure/21972%20-%20.pdf

SCCT guidelines for the interpretation and reporting of coronary computed tomographic angiography.

Purpose To retrospectively evaluate a respiratory-triggered diffusion-weighted (DW) magnetic resonance (MR) imaging sequence combined with parallel acquisition to allow the calculation of pure molecular-based (D) and perfusion-related (D*, f) diffusion parameters, on the basis of the intravoxel incoherent motion (IVIM) theory, to determine if these parameters differ between patients with cirrhosis and patients without liver fibrosis. Materials and methods The institutional review board approved this retrospective study; informed consent was waived. IVIM DW imaging was tested on three alkane phantoms, on which the signal-intensity decay curves according to b factors were logarithmically plotted. Ten b factors (0, 10, 20, 30, 50, 80, 100, 200, 400, 800 sec/mm(2)) were used in patients. Patients with documented liver cirrhosis (cirrhotic liver group, n = 12) and patients without chronic liver disease (healthy liver group, n = 25) were included. The mean liver D, D*, and f values were measured and compared with the apparent diffusion coefficient (ADC) computed by using four b values (0, 200, 400, 800 sec/mm(2)). Liver ADC and D, f, and D* parameters were compared between the cirrhotic liver group and healthy liver group. Means were compared by using the Student t test. Results Signal-intensity decay curves were monoexponential on phantoms and biexponential in patients. In vivo, mean ADC values were significantly higher than D in the healthy liver group (ADC = 1.39 x 10(-3) mm(2)/sec +/- 0.2 [standard deviation] vs D = 1.10 x 10(-3) mm(2)/sec +/- 0.7) and in the cirrhotic liver group (ADC = 1.23 x 10(-3) mm(2)/sec +/- 0.4 vs D = 1.19 x 10(-3) mm(2)/sec +/- 0.5) (P = .03). ADC and D* were significantly reduced in the cirrhotic liver group compared with those in the healthy liver group (respective P values of .03 and .008). Conclusion Restricted diffusion observed in patients with cirrhosis may be related to D* variations, which reflect decreased perfusion, as well as alterations in pure molecular water diffusion in cirrhotic livers.

Liver Cirrhosis: Intravoxel Incoherent Motion MR Imaging—Pilot Study

PURPOSE: To assess whether double arterial phase imaging with multi–detector row helical computed tomography improves detection of hypervascular hepatocellular carcinoma (HCC). MATERIALS AND METHODS: Fifty-one patients with 96 hypervascular HCCs underwent double arterial phase imaging of the entire liver. At measured delay after intravenous administration of 2 mL/kg of contrast medium at a rate of 5 mL/sec, the early and late arterial phase images were obtained serially during a single breath hold with interscan delay of 5.0 seconds. Detector row configuration of 2.5 × 4 mm, pitch of 6, and scanning time of 10.5 seconds for each phase were used. Forty 5-mm-thick reconstruction images were obtained for each phase. Each image set was interpreted separately by three observers, who were unaware of tumor burden in the liver, to detect hypervascular HCC. Sensitivity, positive predictive value, and area below the receiver operating characteristic curve (Az) for early and late arterial phases separately and toget...

Hypervascular Hepatocellular Carcinoma: Detection with Double Arterial Phase Multi-Detector Row Helical CT

PURPOSE: To determine by using multi–detector row computed tomography (CT), in a triphasic hepatic dynamic study, which included single breath-hold dual-arterial phase acquisition, the accuracy and frequency of visualization of the small hepatic arterial and portal venous anatomy with angiographic correlation. MATERIALS AND METHODS: In 62 patients, pre- and postcontrast triphasic helical CT were performed by using a multi–detector row CT scanner, with 2.5-mm detector row collimation, at a pitch of 6. The first and second arterial phases were performed during a single breath hold. One reader, blinded to the results of the angiography, reviewed the first arterial phase images on a cine display to assess hepatic arterial anatomy. Visualization of the portal vein and its branches was assessed by using second arterial and portal venous phase images. RESULTS: Major arterial trunks (celiac, hepatic, superior mesenteric, and left gastric) were depicted in all cases. Visualization of small arteries was as follows:...

Multi–Detector Row Helical CT Angiography of Hepatic Vessels: Depiction with Dual-arterial Phase Acquisition during Single Breath Hold

This study assessed the utility of CT perfusion for quantitative assessment of liver function and fibrosis. Tissue blood flow (TBF), tissue blood volume (TBV), mean transit time (MTT) and hepatic arterial fraction (HAF) were measured with CT perfusion using the deconvolution algorithm in 38 patients with chronic liver diseases and 10 patients without liver disease. Using Child-Pugh classification, 21 patients were classified as Child A, 10 as Child B, and 7 as Child C. In 20 patients, the degree of fibrosis was quantitated in surgically-resected specimens and compared with the perfusion parameters. The mean TBF, TBV, MTT and HAF of patients with-out liver disease were 103.9+/-18 ml/min/100 g, 12.5+/-2.0 ml/100 g, 11.1+/-1.6 sec and 18.4+/-5.6%, respectively (+/-SD). The mean TBF of patients with Child A, B and C were 95.1+/-24, 86.7+/-29 and 75.5+/-6.5 ml/min/100 g, respectively. TBF tended to decrease with the severity of chronic liver disease. The mean HAF of patients with Child A, B and C were 18.6+/-8.3, 29.8+/-11.2 and 40.2+/-11.1%, respectively. HAF of patients without liver disease was significantly different from those of Child B and C (p<0.05, each). However, there were no significant differences in TBV and MTT between each groups. HAF correlated significantly with the degree of fibrosis (R2=0.588, p<0.05). Our results showed that parameters of CT perfusion correlated significantly with the severity of liver fibrosis and cirrhosis. Quantitative measurement of hepatic tissue blood flow by CT perfusion is useful for evaluation of the severity of disease and fibrotic change.

/pdf/assessment-of-the-severity-of-liver-disease-and-fibrotic-48d7rj1wks.pdf

Assessment of the severity of liver disease and fibrotic change: The usefulness of hepatic CT perfusion imaging

OBJECTIVE. The objective of our study was to evaluate the diagnostic impact of varying slice thickness on multidetector CT to optimize detection of hypervascular hepatocellular carcinoma.MATERIALS AND METHODS. Forty-three patients with 87 hypervascular hepatocellular carcinomas (diameter: range, 3-80 mm; mean, 22 mm) and 19 patients with either chronic hepatitis or liver cirrhosis and without hepatocellular carcinoma who had undergone early arterial and late arterial phase imaging of the entire liver on multidetector CT were retrospectively enrolled in this study. The detector row configuration was 2.5 × 4 mm, the pitch was 6, and the scanning time was 10.5 sec for each phase. All patients received contrast medium (2 mL/kg of body weight) at a rate of 5 mL/sec; the mean scanning delay for the early arterial phase was 19.0 sec, and the mean delay for the late arterial phase was 34.5 sec. Eighty 2.5-mm-thick reconstruction images, forty 5-mm-thick reconstruction images, and twenty-six 7.5-mm-thick reconstru...

Multidetector CT: diagnostic impact of slice thickness on detection of hypervascular hepatocellular carcinoma.

Purpose There has been one report that tissue blood flow (TBF) quantification with xenon CT was effective in predicting the therapeutic response to an anticancer drug in pancreatic cancer. The purpose of this study was to evaluate the correlation between the TBF of pancreatic tumors calculated with xenon CT and those with perfusion CT, in order to evaluate whether perfusion CT could replace xenon CT. Materials and methods Nine patients with pathologically proved pancreatic tumors who underwent both xenon CT and perfusion CT were included. Results Quantitative TBF of pancreatic tumors measured by perfusion CT ranged from 22.1 to 196.2 ml/min/100 g (mean+/-SD, 52.6+/-54.8 ml/min/100 g). In contrast, those obtained by xenon CT ranged from 10.3 to 173.6 ml/min/100 g (mean+/-SD, 47.4+/-49.4 ml/min/100 g). There was a good linear correlation between xenon CT and perfusion CT (y=0.8537x+2.48, R2=0.895: p Conclusion The TBF of pancreatic tumors measured by xenon CT and perfusion CT techniques showed a close linear correlation. We can expect that perfusion CT based on the deconvolution algorithm may replace xenon CT to predict the effect of pancreatic tumor treatment with anticancer drugs.

Quantitative tissue blood flow evaluation of pancreatic tumor: comparison between xenon CT technique and perfusion CT technique based on deconvolution analysis.

Masayuki Kudo

Papers

Hypervascular Hepatocellular Carcinoma: Detection with Double Arterial Phase Multi-Detector Row Helical CT

Multi–Detector Row Helical CT Angiography of Hepatic Vessels: Depiction with Dual-arterial Phase Acquisition during Single Breath Hold

Assessment of the severity of liver disease and fibrotic change: The usefulness of hepatic CT perfusion imaging

Multidetector CT: diagnostic impact of slice thickness on detection of hypervascular hepatocellular carcinoma.

Quantitative tissue blood flow evaluation of pancreatic tumor: comparison between xenon CT technique and perfusion CT technique based on deconvolution analysis.