Technical aspects and clinical applications of CT/X, a dynamic CT scanner

How CT happened: the early development of medical computed tomography

As we arrive at the 50th anniversary of the first computed tomography (CT) scan of a live patient, we take this opportunity to revisit the history of early CT development. It is not an exaggeration to say that the invention of CT may represent the greatest revolution in medical imaging since the discovery of x-rays. We cover events over a period of about two decades that started with the realization that accurate cross-sectional soft-tissue detail is possible and could be a significant advance. We describe in some detail the development of the first CT system and then the rapid technical advances during the following years that included the entry of many companies into the field and the circumstances that led many of those entrants to exit the field. Rather than focusing on the specific technical details (which can be found elsewhere), we include stories and events in the hope that broader lessons can be learned. As the first x-ray-based digital imaging modality, CT brought into common use an exceptional tool that benefits countless patients every day. It also introduced dramatic changes to biomedical imaging as a field that continues to influence progress to this day.

Our experiences with parapharyngeal space tumors and systematic review of the literature

OBJECTIVES

To find out the geographical distribution, age, sex, mode of presentation, diagnostic modalities, surgical approaches, postoperative complications, follow-up and histopathology of parapharyngeal space tumors (PFT) through world wide web search (WWWS) and PFT of our series.

MATERIALS AND METHODS

A retrospective study of all PFT seen and treated in S.R.N Hospital, Allahabad between 1990 and 2006 was done. A systematic review of the literature was done through WWWS.

RESULTS

PFT were commonest in the Asian zone. Incidence was highest in the 3rd and 4th decade. Oropharyngeal (100%) and cervical (91.6%) swelling were the commonest presentation. MRI is better than CT scan in evaluating fat plane. Transcervical approach was the commonest. In our series, benign tumors (83.4%) were common, constituting 50% of neurogenic and 16.6% of salivary gland origin.

CONCLUSION

PFT were more prevalent in the Asian zone. Neurogenic tumors were commonest in our study which contradicts the WWWS of having maximum PFT of salivary gland in origin.

Computed tomography of liver tumors

Computed tomographic (CT) scan acquisition speed, interscan delay time, and image quality have significantly improved during the past decade. Thus CT has become a standard against which newer techniques such as magnetic resonance imaging (MRI) are validated. Comparison between CT and other modalities, however, lack validity unless the protocol for each procedure is optimized. The authors emphasize the importance of correct CT contrast enhancement techniques in order to obtain reproducible and optimal anatomical information for defining liver tumor morphology, which will determine resectability. Three-dimensional reconstruction using contiguous volume imaging with appropriate enhancement of vessels and tumor also provides important preoperative evaluation for possible resection. Analysis of the hemodynamic status of the liver parenchyma and of the lesions within it is also possible with contrast-enhanced CT although rarely practiced. With appropriate scanning techniques, excellent anatomical and functional information is obtained simultaneously using CT, although histologic specificity often remains insufficient without biopsy.

Cine computerized tomography

Ultrafast (Cine) CT scanning provides cross-sectional millisecond tomography, and therefore combines digital imaging and high resolution without the need for either cardiac catheterization or any form of ECG gating. Fifty millisecond multilevel scanning at rates of 17 scans per second allows quantitation of left ventricular (LV) function at each tomographic level during a cardiac cycle. Calculations of global and regional ejection fraction can be obtained, and in addition ultrafast CT also has the potential for providing unique data concerning regional wall thickening, mass and even regional myocardial perfusion. Interventional studies with exercise and pharmacological agents have commenced and are currently being evaluated.

Attenuation changes of the normal and ischemic canine kidney. Dynamic CT scanning after intravenous contrast medium bolus

The potential of CT scanning to explore total and regional renal blood flow was evaluated in a dog model with unilateral renal artery stenosis (n = 7, reduction of renal blood flow: 32-75% of base line flow). Attenuation versus time curves were generated for the renal cortex and medulla, as well as for the aorta and renal vein. A fast CT scanner was used which allowed for up to 24 scans/minute at the same level (slice thickness: 10 mm). A total of 10 ml contrast medium was injected into a peripheral vein for each scan series taken. During baseline conditions, the curve of the renal cortex and medulla demonstrated 2 peaks. The first peak was mainly related to early vascular enhancement, whereas the second peak corresponded mainly to the appearance of contrast medium in the distal convolutes and collecting ducts. Ischemia of the kidney resulted in a reduction of the first peak and a flattening of the leading edge slope. Transport of contrast medium through the extravascular compartments of the kidney was delayed during ischemia. Relative renal blood flow was obtained from the CT data by dividing peak enhancement by rise-time as assessed from the cortical curve. All measurements were related to baseline flow and validated by flow measurements using radioactive labeled microspheres (n = 5). Correlation was found to be r = 0.97.

In vivo assessment of left ventricular wall and chamber dynamics during transient myocardial ischemia using cine computed tomography

Using a new computed tomographic (CT) scanner design that uses a rapidly moving focused electron beam, 50-ms CT scans were obtained at 2 axial levels simultaneously through the hearts of 6 dogs in order to analyze left ventricular (LV) wall thickness and cross-sectional chamber area after acute occlusion of the left anterior descending coronary artery (LAD). Ten or fifteen 50-ms CT scans (rate of 17 scans/s through the middle of the left ventricle were performed in 1 second (cine acquisition) during intravenous administration of contrast medium at rest, 60 seconds after acute occlusion of the LAD, and 60 seconds after release of the occlusion. The percent extent of systolic wall thickening of the potentially ischemic anterior segment was 37 +/- 15% (+/- standard deviation) in the control state and -5 +/- 6.5% during LAD occlusion (p less than 0.01). There was no significant difference in the percent change in LV luminal area from end-diastole to end-systole between the control state (50 +/- 19%) compared with LAD occlusion (47 +/- 21%). There were no significant differences in the extent of systolic wall thickening or LV luminal area between the control state and 60 seconds after release of occlusion. The alterations in regional myocardial function during acute ischemia are characterized by wall thinning during systole in the jeopardized segment and no significant change in global LV function. These features can be assessed by cine computed tomography during a solitary heart cycle.

Applications of dynamic-CT, or angio-CT in neuroradiology. A disappointing experience

The authors expose their experience in neuroradiological applications of dynamic-CT (D-CT) or angio-CT. The examinations are performed by means of a G.E. 8.800 CT/T. A special software offers automatic analysis of the region of interest. Vascular and tumoral patients are examined trying to evaluate: (a) the blood flow in patients suffering from transient ischaemic attacks and (b) to estimate the possibilities of D-CT in the evaluation of tumoral vascularity and in the identification of characteristic curves for different kinds of tumors.

Computed tomography of the heart: evaluation of anatomy and function

Diseases of the heart and blood vessels represent one of the most challenging problems for advanced diagnostic imaging systems. Computed tomographic scanning is potentially an ideal cardiac imaging modality since it is a cross-sectional imaging method with very high resolution. Currently available computed tomographic scanners have exposure speeds of 1 to 5 seconds, which are inadequate for the majority of cardiovascular imaging applications. Nevertheless, a variety of limited computed tomographic scanning techniques have been successfully performed in selected patient subgroups. These methods require the administration of contrast medium injected or infused into a peripheral vein, combined with either dynamic computed tomographic scanning or some form of electrocardiographic gated computed tomography. The newer conventional computed tomographic scanners can display anatomic structures in the heart and great vessels with considerable fidelity and provide not only cross-sectional displays but also, by means of computer manipulation, any selected reconstructed images in oblique, coronal or sagittal projections. Feasibility studies indicate improved accuracy of computed tomographic measurements of cardiac chamber volumes. Physiologic measurements include estimation of shunt flows and cardiac output and analysis of myocardial wall thickening. The full potential of computed tomography should be reached once fast, multiple slice, computed tomographic scanners using scanning electron beam techniques become available. The prototype CVCT (cine computed tomographic C-100 scanner) designed at the University of California, San Francisco, is now undergoing evaluation. This instrument images up to eight contiguous slices at the rate of 16 to 24 images/s. The computed tomographic scanner specifically designed for cardiac imaging should extend the utility of computed tomography in the evaluation of cardiac diseases and the study of cardiovascular physiology.

Evaluation of early postoperative coronary artery bypass graft patency by contrast-enhanced computed tomography

Fifty patients with 117 coronary bypass grafts were studied by contrast-enhanced computed tomography at an average of 5 +/- 4 days after surgery to determine if this technique was a feasible method for detecting early postoperative graft occlusion. The study was limited in only three patients because of incisional chest pain (one patient) or multiple metal clips attached to the graft (two patients). The distal patency of sequential grafts cannot be determined by current techniques. There was a lower graft patency rate (70%) in the 10 patients with perioperative myocardial infarction than in the 40 (95%) without (p less than 0.025), but most regions of infarcted myocardium were perfused by patent grafts. There were eight graft occlusions in eight patients. The graft occlusion rate (30%) was significantly higher (p less than 0.025) in grafts with intraoperative flows less than 45 ml/min. The postoperative complications of myocardial dysfunction, arrhythmia and coronary artery spasm did not correlate with graft occlusion. Early graft occlusion is uncommon (7%) and usually occurs in grafts with low flows or severe distal disease (seven of eight grafts), or both. Thus, the need for early reoperation is very infrequent. It is concluded that contrast-enhanced computed tomography is feasible for the assessment of coronary bypass graft patency. Because early graft occlusion is unusual the technique may be an ideal noninvasive screening method.

Dynamic computed tomography and functional imaging in cerebral vascular anomalies

Dynamic computed tomography was performed on patients with cerebral vascular anomalies, the density-versus-time curves were derived, and the gray-scale functional images demonstrating the pixel-by-pixel distribution of several flow parameters were processed. This noninvasive method was found to be useful not only in delineating the vascular anomalies with their afferent and efferent vessels, but also in detecting the abnormal flow patterns within and outside the vascular anomalies. Limitations and distinct advantages of this technique are briefly discussed.

In vivo assessment of left ventricular wall and chamber dynamics during transient myocardial ischemia using prospectively ECG-gated computerized transmission tomography

Seven dogs were evaluated with prospective ECG-gated computerized transmission tomography (CTT) to analyze left ventricular (LV) wall thickness and cross-sectional chamber area after acute occlusion of the left anterior descending coronary artery (LAD). ECG-gated CTT scanning during i.v. administration of contrast material was performed over the mid-left ventricle at rest, after acute occlusion of the LAD and 30 minutes after release. The extent of systolic wall thickening (EWTh) of the anterior (potentially ischemic) segment was 39.8 +/- 8.8% (SEM) in the control state and -26.0 +/- 4.7% during LAD occlusion (p less than 0.01). The nonischemic septum demonstrated a compensatory increase in EWTh, from 28.6 +/- 3.5% to 46.4 +/- 6.1% during LAD occlusion (p less than 0.05). The end-diastolic LV luminal area (LVA) increased from 17.4 +/- 0.8 cm2 in the control state to 21.0 +/- 1.1 cm2 during LAD occlusion (p less than 0.01). End-systolic LVA also increased, from 11.0 +/- 0.9 to 15.2 +/- 1.1 cm2 (p less than 0.01). In addition, the percent change in LVA from end-diastole to end-systole declined from 37.4 +/- 3.8% during control to 28.0 +/- 2.6% during LAD occlusion (p less than 0.02). In conclusion, gated CTT demonstrates that the alterations in acute ischemia are characterized by changes in regional wall thickening dynamics, consisting of wall thinning during systole in the jeopardized segment and compensatory increase in the extent of systolic thickening in the normal segment, and changes in global LV function, consisting of an increase in the LVA and a decrease in the percent change of LVA during systole. Gated CTT may be useful for monitoring regional and global effects of ischemia when subjects can be studied in the supine position and with respiration suspended for 45 seconds.

CT attenuation ratio of myocardium and blood pool in the normal and infarcted canine heart

The CT attenuation of the myocardium varies with the contrast medium concentration of the blood at steady state. The demonstration of myocardial infarcts depends on the differences of CT numbers within the myocardium. In order to make possible objective estimation and measurement of myocardial ischemia the normal regression between CT attenuation of the blood pool and the myocardium has been determined in 13 dogs. The relationship has been applied to 15 dogs with experimental infarcts examined with contrast enhanced CT. The results indicate that this method may be of value in identifying and sizing myocardial infarcts of different ages in patients.

Dynamic volume imaging of moving organs

The Dynamic Spatial Reconstructor system has been developed to dynamically (up to 60/sec) image the entire 3-D volume (up to 240 adjacent 1-mm-thick transverse sections) encompassing moving organs of the body, particularly the heart and lungs, or the circulation in any organ. This capability permits accurate regional and global measurements to be made of the important relationships between structure and function within and among these organs, which in turn facilitates achievement of new insights into the basic physiological processes of these organs, and promises increased sensitivity and specificity in the diagnosis of pathology that affects normal organ function. This article explains the biomedical and technological rationale for development of the DSR, describes the design concepts and practical operation of the system, and presents preliminary results obtained with the system, including initial data from one of the first patient studies.

ECG synchronized computed tomography in clinical evaluation of total and regional cardiac motion: comparison of postmyocardial infarction to normal hearts by rapid sequential imaging

Computed tomograph (CT) of the heart was performed using the JEOL Dynamic Scanner, which provides CT cardiac images with minimal radiation and within a short period of time. ECG-synchronized CT was undertaken at various phases of the cardiac cycle every 0.04 second. Approximately 30 minutes of scanning was necessary to obtain a series of CT images of one complete cardiac cycle. In contract to 24 normal subjects, 38 patients with recent or remote myocardial infarction (MI) demonstrated hypokinetic, akinetic, or paradoxical movement of the ventricular segment corresponding to the MI sites predicted by ECG. The sequential cardiac area curve was useful in evaluating instantaneous changes of cardiac dimension, extent of ventricular contraction, and regional dyssynergy. ECG-synchronized CT studies using Somatom contrast dye enhancement in selected patients allowed sequential assessment of left ventricular cavity size and wall motion.

The Dynamic Spatial Reconstructor: An X-Ray Video-Fluoroscopic CT Scanner for Dynamic Volume Imaging of Moving Organs

The trend in development of X-ray computed tomography systems over the past decade has been toward faster and faster scanners, with comcomitant improvement in image quality. The preliminary results from the DSR scanner suggest the advent of two new, powerful dimensions in X-ray computed tomography high temporal resolution and synchronous volume scanning. That is, true stop-action, full three-dimensional imaging at a high repetition rate is possible with CT scanners. Such capabilities promise to make possible new basic investigative and clinical studies of the structural-to-functional relationships of moving organ systems like the heart and lungs, and of the circulation in any organ of the body. Current state-of-the-art CT technology holds promise of exciting new clinical and research capabilities, such as quantitative analysis of regional blood flow and perfusion, simultaneous measurement of physiologic function and anatomic structure, and differential diagnosis of disease based on determination of tissue composition in any organ or region of the body, with a sensitivity and specificity not possible before.