Transaxial Scans Research Articles

Radiology of the distal radioulnar joint and the ulnocarpal complex

X-ray images exposed in neutral position and radiocarpally centred are essential in imaging of the distal radioulnar joint (DRUJ). The anatomic orientation of the DRUJ is favourable for acquiring transaxial scans to display its anatomy, subtle derangements, osteoarthritis and intra-articular fractures free from superpositions. The triangular fibrocartilage complex (TFCC) is the most important stabilizer of the DRUJ. Provided that afocused clinical indication is given, high-resolution images are acquired, and an intra-venous or intra-articular contrast-agent is applied, all TFCC structures and destabilizing lesions can be displayed with the use of CT and MRI.

WE‐C‐330A‐08: An Efficient Morphometric Skull Atlas for Image Guided Radiotherapy

Purpose: We describe an efficient method to extract the outer skull features from CT transaxial slices for use in IGRT. Method and Materials: A Bezier curve B(t) was fit to four sections of the outer skull on CT slices at 0.3cm spacing. B(t) is a parametric equation defined by two anchor points (A1,A2) and two control points (C1,C2) such that for 0⩽t⩽1. The parameter t is sampled to create a sequence of points at 0.3cm interval. The atlas consists of all the Bezier points and can be transformed by rotation R and translation T such that . Thirty‐two points on the anterior‐posterior and right‐lateral Portal Images are digitized for analytical computation of setup error. The position and orientation (i.e. pose) of the atlas with the minimum Hausdorff Distance (HD) between the PI points and the outer projected atlas contour determines the homogenous transformation. Results: Manual draw‐by‐wire technique can take up to 15 minutes per slice. The total time is reduced by 50% for similar size patients in nearly identical positions. The overall accuracy was determined to be 0.15 cm. A semi‐automatic technique with improved accuracy of 0.1 cm was investigated using simulated annealing. An automatic algorithm using monochromatic bit maps with edge detection was also evaluated. For 30 CT slices, the complete atlas is defined by only 360 points. Setup error for a clinical case was measured and the effects of pure rotation mimicking translation quantified. Conclusion: We have demonstrated that a series of four piecewise continuous Bezier curve segments can accurately extract the outer skull feature from a CT transaxial scan. A patient specific atlas can be quickly morphed from the generic atlas. The atlas has been shown to be clinically useful for 3D analysis of setup error and theoretical quantitative analysis of pure rotation.

A Molecular CT Blood Pool Contrast Agent

Rationale and Objectives A molecular-based computed tomographic (CT) contrast agent with prolonged vascular residence time is needed for vascular and tumor imaging. No particulate agents have reached clinical practice due to nonspecific macrophage activation. The authors' objective was to synthesize a water-soluble macromolecular agent. Materials and Methods Dysprosium-DTPA-dextran was synthesized through activation of the hydroxyl units of dextran PM40 with allylbromine and subsequent reaction with amino ethanethiol to produce amino-terminated leashes. These leashes were then coupled to DTPA by means of the mixed anhydride method. Complexation of dysprosium by DTPA-dextran was achieved in an acidic solution of 0.2 M dysprosium chloride. One rabbit with a VX2 tumor was imaged with [Dy]DTPA-dextran (0.5 mL, 3.1 g, 1.15 mmol of dysprosium per kilogram). Transaxial scans were acquired through the liver and tumor for 45 minutes. A second healthy rabbit was imaged with Optiray-320 (6.0 mL, 5.0 mmol of iodine per kilogram) at 1-minute intervals for 10 minutes and again at 20 minutes. Results Each dextran PM40 molecule (diameter, 8.8 nm) contained 95 [Dy]DTPA groups, increasing its average molecular weight from 40,500 to 101,537 g/mol. The baseline-corrected inferior vena cava (IVC) enhancement for [Dy]DTPA-dextran decreased, with an 8-minute half-time during the first 15 minutes followed by a nearly zero slope for the rest of the observation period. The IVC remained brighter than liver throughout the observation period. The solid portion of the tumor was enhanced by 5–10 CT numbers, rendering areas of necrosis more apparent. The baseline-corrected IVC curve for Optiray-320 also demonstrated two phases, with half-times of 2.5 and 45 minutes. The IVC became less dense than liver within 5–8 minutes. Conclusion [Dy]DTPA-dextran is water soluble and can be synthesized without intermolecular cross-linking to carry a high load of dysprosium. It provides blood pool enhancement characteristics with a long intravascular dwell time.

Strategies for cardiac CT imaging.

We review the scanning techniques for cardiac CT imaging with single slice and multislice scanners. Combined with prospective triggering for transaxial scanning and retrospective gating for helical scanning the potential advantages and the basic limitations are discussed. Based on those theoretical considerations, the major conclusion is that high resolution data sets with isotropic spatial resolution can be acquired with quadslice, spiral scanning, only. First clinical results support this conclusion.

Evaluation of gastric emptying and motility in diabetic gastroparesis with magnetic resonance imaging: effects of cisapride

OBJECTIVE: The motor mechanisms that underlie both slow gastric emptying in diabetic gastroparesis and its acceleration by cisapride are poorly understood. We have recently shown that magnetic resonance imaging (MRI) allows concurrent evaluation of both gastric emptying and regional gastric motility. METHODS: Emptying and motility were measured in eight diabetic patients with previously demonstrated delayed gastric emptying using a rapid MRI technique during oral administration of cisapride and placebo. Studies were performed in a double blind fashion and each patient acted as his own control. Subjects were studied supine for 120 min in a 1.5 Tesla MRI scanner after ingestion of 500 ml of 10% Intralipid. Gastric emptying corrected for the volume of secretions was determined every 15 min using transaxial scans. Each transaxial scan was followed by 120 coronal scans at 1 s intervals. Coronal scans were angled to provide simultaneous imaging of the proximal and distal stomach. MRI studies were also performed in seven diabetic patients with normal emptying who served as disease controls. RESULTS: Emptying was slower in the gastroparetic patients (t 1/2: 124 ± 10 min) compared to patients with normal emptying (81 ± 9 min, p < 0.05). Cisapride accelerated gastric emptying (74 ± 5 vs 124 ± 10 min) in patients with gastroparesis. The contraction amplitudes in the proximal stomach of gastroparetic patients were increased during cisapride treatment (17.2% ± 1.8% vs 13.2% ± 0.6%; p < 0.02), whereas antral contraction frequency, amplitude, and velocity were unchanged. CONCLUSIONS: We conclude that cisapride-induced acceleration of liquid gastric emptying in diabetic gastroparesis does not appear to result from changes in antral contractility, but may be related to changes in proximal gastric tone or gastric outlet resistance.

Effect of artifacts due to flowing blood on the reproducibility of phase-contrast measurements of myocardial motion.

The reproducibility of myocardial motion trajectories calculated from cine phase-contrast (PC) velocity data is reduced by artifacts due to the inconsistent motion of intracardiac blood. Spatial presaturation reduces these artifacts but requires a longer sequence TR, with a potentially negative effect on trajectory accuracy and reproducibility. We investigated the effect of spatial presaturation on trajectory reproducibility. A mid-ventricular transaxial slice was imaged in five normal volunteers. The same slice was imaged three times each with sequences using spatial presaturation or not. Because the most serious artifacts originate in the heart chambers and propagate in the phase-encoded direction, myocardial regions that were in line with the heart chambers (in the phase-encode direction) had the highest artifact level in the scans without spatial presaturation. The reproducibility of trajectories for regions placed in these areas (the anterior wall, septum and posterior wall in the transaxial scans with phase encoding in the anterior-posterior direction) improved by a factor of two when presaturation was used (P < .001). In areas that were not in line with the heart chambers (eg, the anterior aspect of the lateral wall in the transaxial scans), the effect of presaturation was not significant. These results correlate well with the measured reduction in artifact level. The reproducibility of myocardial motion trajectories over large areas of the heart is improved to approximately 1 mm when presaturation is used. Therefore, use of presaturation is recommended for myocardial motion studies using cine PC velocity data.

Spiral CT angiography in the assessment of abdominal aortic aneurysms after stent grafting: value of maximum intensity projections.

Our goal was to evaluate the value of maximum intensity projections (MIPs) rendered from spiral CT in the assessment of abdominal aortic aneurysms after stent graft implantation. Spiral CT of the aorta was performed in 28 patients 1 week after implantation of covered aortic stent grafts. MIPs were evaluated in a blinded fashion. Transaxial scans and intravenous angiographs were considered the reference standard. Stent deformity was evident on the MIPs in 5 cases and stent angulation was seen in 24 cases. The excluded aneurysmal sac was visualized in 14 (50%) cases. MIPs depicted the patent inferior mesenteric artery in 20 of 23 cases (87%). Renal artery occlusion (n = 3), leaks (n = 8), and parietal thrombi, (n = 3) were detected on the MIPs in all cases. MIPs are a valuable tool in the assessment of aortic stent grafts.

Gastric motility measurement by MRI

The motor mechanisms associated with gastric emptying of nutrient liquids are unclear. Gastric emptying and motility were determined in seven healthy volunteers using an MRI technique following ingestion of 500 ml of (1) 10% and (2) 25% dextrose labeled with 1 mM Gd-DOTA. Emptying was determined with transaxial scans and motility during fast coronal scans 1.2 sec apart. Emptying was slower after ingestion of 25% dextrose. Following both meals, proximal gastric diameter remained relatively constant, while antral contractile frequency and depth varied markedly. These variations were greater after 10% dextrose. These studies suggest that antral motility changes contribute to slowing of gastric emptying by nutrient meals.

Evaluation of the Role of Coronal and Sagittal Axial CT Scan Reconstructions for the Imaging of Acetabular Fractures

In order to assess acetabular joint congruity and postoperative reconstructions, a study was undertaken to evaluate the use of coronal and sagittal reconstruction of transaxial CT scans. The 28 acetabular fractures evaluated included 10 posterior wall, 11 transverse, 6 associated both column, and 1 nonclassifiable medial wall fracture. In 7 cases the surgical approach was modified from the original preoperative plan based on the coronal and sagittal CT reconstruction results. In 2 other cases associated both column fractures were treated nonoperatively based upon the coronal and sagittal CT reconstruction results. In 2 cases intraarticular fracture fragments were shown to be larger than expected from the original studies. In all cases of marginal impaction (N = 10) coronal and sagittal CT reconstruction showed that the fragments were larger than they appeared to be on the transaxial CT scan. Coronal and sagittal CT reconstruction provided more detailed evaluations of these complex fractures than other studies.

Estimation of body fat and body fat distribution in 11-year-old children using magnetic resonance imaging and hydrostatic weighing, skinfolds, and anthropometry.

From early pubescence, both degree and distribution of fatness have been related to health risk factors. Measures that are capable of providing estimates of overall fatness and the extent of high risk fat patterning are, therefore, advantageous. The objective of this study was to compare estimates of body fatness and fat distribution using magnetic resonance imaging with the traditional methods of hydrostatic weighing, skinfolds, and anthropometry in 11-year-old boys and girls. Subjects were 25 boys and 25 girls, representative of their age cohort's body mass index (BMI) range. Total fat using MRI was obtained by summing subcutaneous and internal fat areas from four transaxial scans at the chest, waist, hips, and thigh. Mean MRI total fat (MRI FAT) was 357 (±152) cm2 with a range of 172-739 cm2 for boys and 427 (±174) cm2 with a range of 209-995 for girls. Correlation analyses revealed strong relationships between MRI FAT and UWW FAT (r = 0.73 boys, r = 0.77 girls), and the sum of four skinfolds (r = 0.94 boys, r = 0.88 girls). Analysis of the MRI data alone revealed that MRI FAT variation is largely explained by subcutaneous fat deposition at the waist in boys and at the level of the buttocks in girls, with most skinfolds correlating highly with MRI FAT in both sexes. Results of stepwise multiple regression showed that an abdominal skinfold and thigh circumference explained 95% of MRI FAT in boys, and 86% of the variance in girls. These data show that magnetic resonance images can provide useful information for the identification of discriminating field measures of fatness and its distribution in 11-year-old children. © 1994 Wiley-Liss, Inc.

Transfer of CT scan data to diagnostic casts.

A technique for the transfer of diagnostic information from transaxial CT scans to diagnostic casts is presented. A duplicate of the patient's existing prosthesis is utilized as a custom tray and an impression of the edentulous arch is made. The data from the transaxial radiographs are transferred to the diagnostic cast using anatomical landmarks as reference points. The marked cast can be used by the surgeon and the restorative dentist for optimal implant placement.

Annealing studies on ion implanted diamond

In this study we report on an investigation of the degree of damage recovery after multi-implantation of 12C into diamond as a function of dose and annealing temperature. Three different doses spread over energies of 150, 120, 80 and 50 keV at an implantation temperature of −190°C were used: 5.25 × 10 15, 2.9 × 10 15 and 5.25 × 10 14 ions cm 2 . After the completion of each implantation the diamond was allowed to warm up to room temperature, whereupon ion channeling of 1.0 MeV protons was used to locate the three major diamond channels, the (100), (111) and (110). Finally 1.2 MeV He + ions were then used to produce trans-axial scans of each channel to a depth of ~ 2700 Å. The diamond was then annealed at 630, 1050, 1300 and finally 1500°C in an inert argon atmosphere. Channeling measurements on each of the axes were repeated after each anneal. The results indicate that damage removal is initiated from the surface, and advances progressively into the diamond as the annealing temperature is increased. The highest dose of 5 × 10 15 ions cm 2 introduces thermally stable defects into the damaged region which are not observed for the other implantation doses.

Musculoskeletal haemangiomas: comparison of MRI with CT

MRI and CT findings were reviewed from 11 patients with musculoskeletal haemangiomas. With MRI, morphological characteristics and extent of haemangiomas were optimally demonstrated on T2-weighted spin echo scans. High-resolution contrast-enhanced CT provided equivalent information regarding lesional characteristics and extent for small, localized haemangiomas. In CT evaluation of the extent of large haemangiomas, the radiation dose, transaxial scan plane, amount of intravenous contrast medium required and the necessity for correct timing of post-contrast scans became limiting factors. For such lesions, particularly those extending into the trunk, MRI supplemented by a plain radiograph is the optimum method of evaluation.

Magnetic resonance imaging of the hila and mediastinum.

In the diagnosis of chest diseases, MR imaging has been shown to be most helpful in the evaluation of hilar and mediastinal lesions. The detection of intrathoracic abnormalities is technique-dependent, and imaging with both short and long repetition and echo times is necessary. ECG gating and sagittal or coronal images supplement transaxial scans in some patients. MR allows the diagnosis of mediastinal vascular lesions and the differentiation of mediastinal mass and vessel without contrast agents. It provides diagnostic information quite similar to that of CT in patients with mediastinal mass, but spatial resolution is somewhat poorer. In patients with hilar mass, MR is superior to CT in identifying the mass and distinguishing it from normal structures.

Case report: CT findings in lumbosacral agenesis

This case describes a newborn paraplegic male with lumbosacral agenesis and related congenital anomalies, including bilateral hip dislocations, arthrogryposis, talipes equinovarus, as well as neurogenic bladder with urine incontinence. An extradural tumor, surgically excised and diagnosed as a lipoma, was identified on computed transaxial scans to be adjacent to an abruptly terminating dural sac. Caudal to the sac the scans demonstrated partial fatty replacement of muscle bundles and direct articulation of the iliac wings. A follow-up myelogram delineated the subarachnoid space, but could not distinguish the tumor from a deformed sac secondary to lumbar derfects. Computed tomography is thus recommended as part of the general radiologic protocol for fully evaluating the spatial orientation and anomalies of this spinal defect.

Multi-planar reconstruction as a method of eliminating streak artifact in computed tomographic images

Digitalized information obtained in transaxial scans may be employed in multi-planar reconstruction as a method to reduce artifact. In this type of situation the reconstructed images may have a higher diagnostic quality than the original images. With oblique reconstruction packages, which were not available on our machine at the time of the case, even higher quality secondary images might be generated.

Device for correlating CT and radiation therapy portal images.

Computed tomographic (CT) scanning holds great promse for precise localization of radiotherapy treatment volumes and corresponding high precision treatment planning. CT scanners are uniquely able to conveniently localize organs, tissue structures, and tumor volumes in true anatomic relationships. This has obvious value both in design of the treatment and in evaluating the response to it [1]. Algorithms currently being developed for CT reconstruction may yield attenuation coefficients, atomic number, or other physical properties of imaged structures which in turn may allow treatment planning and dose distribution studies incorporating homogeneity and contour corrections. A potential valuable feature for future development would be threedimensional treatment planning systems [2]. Basic to all these applications is the seemingly simple yet important problem of correlating CT transaxial scan levels with typical full-size nadiographs encompassing the treatment volume as obtained from simulators, portal films, or routine diagnostic radiographic views. This paper describes a technique that can accomplish this correlation in a simple, straightforward, accurate manner. In addition, the device used minimizes the production of artefacts usually produced by inclusion of foreign objects into CT scan fields. Such artefacts hinder accurate tissue-boundary localization and also seriously hamper calculations using digital CT values for dose distribution studies.

Optical inverse radon transform

Mathematical formulation of an optical processesor that implements the inverse radon transform is described. This operation is of use in X-ray computed tomography, transaxial scanning and other image construction systems. The optical system outlined uses the convolution of two two-dimensional functions to achieve the inverse radon transform by a new implementation method.