The impact of computed tomography on neuroradiologic practice

History and evolution of brain tumor imaging: insights through radiology

This review recounts the history of brain tumor diagnosis from antiquity to the present and, indirectly, the history of neuroradiology. Imaging of the brain has from the beginning held an enormous interest because of the inherent difficulty of this endeavor due to the presence of the skull. Because of this, most techniques when newly developed have always been used in neuroradiology and, although some have proved to be inappropriate for this purpose, many were easily incorporated into the specialty. The first major advance in modern neuroimaging was contrast agent-enhanced computed tomography, which permitted accurate anatomic localization of brain tumors and, by virtue of contrast enhancement, malignant ones. The most important advances in neuroimaging occurred with the development of magnetic resonance imaging and diffusion-weighted sequences that allowed an indirect estimation of tumor cellularity; this was further refined by the development of perfusion and permeability mapping. From its beginnings with indirect and purely anatomic imaging techniques, neuroradiology now uses a combination of anatomic and physiologic techniques that will play a critical role in biologic tumor imaging and radiologic genomics.

Linear fractures invisible on routine axial computed tomography: a pitfall at radiological screening for minor head injury

Computed tomography (CT) is now widely used as the only screening method for fractures in patients with head injury. However, clear depiction of a fracture requires a discontinuity in the skull, so linear fractures parallel to the CT slice may not be visualized. We retrospectively evaluated 302 patients with minor head injuries aged from 0 to 91 years, who had undergone routine skull radiography (anteroposterior and lateral views) and head CT to study these types of fracture and discuss the risk of nondetection. Three patients had linear fractures (0.99%) that were invisible on bone window axial CT but detected on skull radiography, which all ran parallel to the scan slice. Two patients developed acute epidural hematoma or traumatic subarachnoid hemorrhage. Evaluation of head injury by only axial CT may miss such fractures and result in sequelae, so diagnosticians should be alert to the possible presence of this type of fracture.

Linear fractures occult on skull radiographs: a pitfall at radiological screening for mild head injury

BACKGROUND

Skull radiography is widely used to screen for fractures in patients with mild head injury. However, the clear depiction of a fracture requires a gap in the skull separated by the fracture that is wide enough to allow the passage of x-rays. We studied atypical linear fractures that were not visualized clearly, because a specific anatomical configuration hampered the passage of x-rays.

METHODS

We retrospectively evaluated 278 patients with mild head injuries who had undergone routine skull radiography (anteroposterior and lateral views) and head computed tomography (CT). We found that some patients negative for linear fracture on skull radiographs were positive on bone window CT scans.

RESULTS

Of the 278 patients aged between 2 months and 66 years, 8 (2.9%) manifested a linear fracture on CT scans that presented as a cross section of the fracture oblique to the direction of the x-rays. Four of the 8 developed acute epidural hematoma; 2 of these patients underwent craniotomy.

CONCLUSIONS

Radiographic study returned false-negative results, because x-rays were absorbed by the double-layered skull along fractures whose cross section was oblique to the direction of the x-rays. The evaluation of head injury by radiography only may miss these fractures and their undetected presence may result in sequelae such as intracranial hematoma.

Vision 20/20: increased image resolution versus reduced radiation exposure

This is a review of methods, currently and potentially, available for significantly reducing x-ray exposure in medical x-ray imaging. It is stimulated by the radiation exposure implications of the growing use of helical scanning, multislice, x-ray computed tomography for screening, such as for coronary artery atherosclerosis and cancer of the colon and lungs. Screening requires high-throughput imaging with high spatial and contrast resolution to meet the need for high sensitivity and specificity of detection and classification of specific imaged features. To achieve this goal beyond what is currently available with x-ray imaging methods requires increased x-ray exposure, which increases the risk of tissue damage and ultimately cancer development. These consequences limit the utility of current x-ray imaging in screening of at-risk subjects who have not yet developed the clinical symptoms of disease. Current methods for reducing x-ray exposure in x-ray imaging, mostly achieved by increasing sensitivity and specificity of the x-ray detection process, may still have potential for an up-to-tenfold decrease. This could be sufficient for doubling the spatial resolution of x-ray CT while maintaining the current x-ray exposure levels. However, a spatial resolution four times what is currently available might be needed to adequately meet the needs for screening. Consequently, for the proposed need to increase spatial resolution, an additional order of magnitude of reduction of x-ray exposure would be needed just to keep the radiation exposure at current levels. This is conceivably achievable if refraction, rather than the currently used attenuation, of x rays is used to generate the images. Existing methods that have potential for imaging the consequences of refracted x ray in a clinical setting are (1) by imaging the edge enhancement that occurs at the interfaces between adjacent tissues of different refractive indices, or (2) by imaging the changes in interference patterns resulting from moving grids which alter the refraction of x rays, that have passed through the body, in a predictable fashion, and (3) theoretically, by an image generated from the change in time-of-flight of x-ray photons passing through the body. Imaging phase shift or change in time-of-flight, rather than attenuation, of x-ray photons through tissues presents formidable technological problems for whole-body 3D imaging. However, if achievable in a routine clinical setting, these approaches have the potential for greatly expanding the use of x-ray imaging for screening. This overview examines the increased contrast resolution and reduced radiation exposure that might be achievable by the above-mentioned methods.

The effect of helical computed tomography on diagnostic and treatment strategies in patients with suspected pulmonary embolism

BACKGROUND

Helical computed tomography (CT) has been proposed as a first-line test for the diagnosis of pulmonary embolism. How the test affects the diagnostic evaluation of patients with suspected pulmonary embolism is unknown.

METHODS

We examined a cohort of 360 patients evaluated for pulmonary embolism at a teaching hospital in the 4 years following the introduction of the helical CT scan. We collected patient demographic and clinical data to calculate the pretest likelihood of pulmonary embolism; we then read the test results and determined rates of further testing and treatment for pulmonary embolism.

RESULTS

After the helical CT scan became available, the number of patients referred for pulmonary embolism testing increased markedly from 170 to 624 total evaluations during 1997 to 2000 (P <0.01). This rise was due to increased use of the helical CT scan (9% to 83% of evaluations, P <0.01) as the use of ventilation-perfusion scanning (79% to 17%, P = 0.03) and pulmonary angiography (12% to <1%, P <0.01) fell. There was no change in the pre-test likelihood of disease over time, but the percentage of scans that were positive for pulmonary embolism rose (14% to 32%, P =0.02). Clinicians treated all patients who had a positive CT scan, but became less likely over time to order further testing for patients who had a negative scan (30% to 12%, P = 0.02).

CONCLUSION

At this academic medical center, introduction of the helical CT scan had a profound effect on the evaluation of pulmonary embolism, resulting in more frequent use of the CT scan, and more frequent diagnosis and treatment of pulmonary embolism, despite no change in the pretest probability of disease. Future studies should confirm our findings and determine whether increased detection of pulmonary emboli results in improved outcomes.

Cardiac computed tomography imaging: a history and some future possibilities

Cardiac computed tomography (CT) is a special subset of CT, a subject about which much has been written in terms of the underlying concepts and mathematics and the sociologic impact. Cardiac CT has passed through three, chronologically overlapping, developmental stages and is now in its fourth stage of development. The first stage was fluoroscopy-based CT (1972-1995) stimulated by physiologic research needs, and the next was clinical CT-based exploration (1975-1980) of the potential of clinical CT in cardiology. This was followed by the electron beam CT-based stage (1980-present), which was the first CT approach applicable to clinical cardiology. Finally, volume-scanning CT imaging methods achieved with multislice scanning approaches of helical CT and by flat panel-based CT (1990-present), show great promise for clinically applicable CT of the cardiovascular system.

Applications of time-series analysis: a case study on the impact of computer tomography

Time-series techniques are applied to an analysis of the use of neurodiagnostic procedures in Athens, to evaluate the effect of the introduction of computer tomography. Results confirm the usefulness of such techniques, but illustrate the dependence of their successful application on the nature and quality of data.

Evaluation of the suprasellar cistern by computed tomography

The normal suprasellar cistern is a five- or six-pointed, starshaped, fluid-filled structure as demonstrated by computerized axial tomography (CAT). At various levels the normal suprasellar cistern contains the major intracranial vessels and their anastomotic channels, the optic nerves, chiasm, and infundibular stalk. The existence of lesions, either intrinsic structures of or extrinsic structures contiguous to the suprasellar cistern can be detected by their effect on the normal anatomy of the suprasellar cistern or by filling defects produced when studied with metrizamide cisternography.

Discrepancies between radionuclide and computed tomographic scans in detecting secondary neoplastic involvement of the brain

A radionuclide (RN) brain scan and a computed tomographic (CT) brain scan were performed on the same patient within one month on 207 occasions between February 1978 and October 1979 in order to investigate secondary neoplastic involvement of either metastatic or lymphomatous nature. The two scans were read independently of each other. There was a significant difference between the results of the two techniques in 26 of the 207 cases (13%). In 15 cases, the RN brain scan found clinically suspected secondary neoplastic involvement that was not detected by CT. In the other 11 cases, lesions detected by CT were not detected with the RN scan. Discrepancies were more frequent in patients with lymphoma than in patients with carcinoma.

Diagnostic and therapeutic impact of computerized tomography in patients with malignant brain tumours: South Australian experience

The incidence of malignant brain tumours in the South Australian population has been determined for two six-months periods before and after the introduction of computerized tomography (CT). The impact of CT on diagnosis and short-term patient status has been analysed in patients with astrocytoma or glioblastoma multiforme. CT has significantly altered neuroradiological practice in these patients, but appears to have had little impact on prognosis or outcome.

Changes in neurological practice in South Australia after the introduction of computerized tomography

There has been no significant change in the age distribution of patients undergoing neuroradiological investigations after the introduction of computerized tomography (CT) in South Australia. The referral pattern has not changed, and adequate clinical neurological assessment was apparent both before and after the availability of CT, with the application of CT being selective rather than additive. Initial impression suggests some reduction in bed utilization after the introduction of CT.

Clinical evaluation of computed tomographic scanning

Computed tomographic (CT) head scans were performed on 100 patients in a neurology ward. The CT scan was diagnostic in 67 patients and suggestive in a further three patients. Computed tomographic scans were most likely to be diagnostic in patients whose symptoms at presentation could be classified as "traumatic intracranial lesion", "space-occupying lesion", "acute cerebrovascular lesion", "dementia", and "epileptic disorder", and much less likely to be diagnostic if a patient presented differently. In all cases where the CT scan was diagnostic. It was considered that, had a CT scan not been available, alternative tests such as nuclear scan, cerebral angiography or pneumoencephalogram (PEG) would have been performed and would also have been diagnostic; no impact of the CT scan on diagnosis, therapy or patient outcomes was documented. However, in patients who received a CT scan, there was a 91% reduction in the PEGs, 85% reduction in cerebral angiograms, a reduction of 73% in nuclear scans and 31% in electroencephalograms. Computed tomographic scanning costs no more than the tests it replaces in the clinical setting studied, and offers significant advantages in patient comfort and safety.

Impact of computerized tomography on neuroradiological investigations in South Australia

Although there has been a reduction in cerebral angiographic (33%), pneumoencephalographic (70%) and radionuclide brain scanning (28%) investigations since the introduction of computerized tomography in South Australia, there has been a significant increase (56%) in the total number of neuroradiological investigations performed. At the same time, the number of patients who underwent neuroradiological investigations has risen by 75%. This is equivalent to approximately one person in every 290 per year.

Computed tomography in diagnosis of abdominal masses in infancy and childhood. Comparison with excretory urography

Computed tomography (CT) of the abdomen and pelvis was performed in 26 instances of suspected mass in 24 infants and children. The information obtained was compared to that of standard abdominal radiography and excretory urography (IVP). Results were analyzed prospectively. CT was able to detect and define masses more precisely than abdominal radiography and IVP. The information obtained by CT, in a single noninvasive examination emitting minimal ionising radiation, seems comparable to that offered by a combination of multiple radiological and other imaging procedures. It is conceivable that with accumulating experience and further technological improvement CT may become an excellent screening procedure in the investigation of abdominal and pelvic masses. The high cost of CT scanning may be offset by the benefits cited.

CT in evaluation of the circle of Willis

The method of visualizing the circle of Willis intentionally on contrast-enhanced CT scan was studied. The incidence of circle of Willis in our series was 86%. Only mild side effects were observed, in 7.5% of cases. CT of 60 proven cerebral aneurysms were reviewed and aneurysm was detected in 57%. This method has the potential to be a noninvasive screening procedure for evaluation of suspected cerebral aneurysm, as well as evaluation of marked arteriosclerosis, occlusion of major arteries, and mass effect of parasellar tumors.

Computed tomography of the skeletal system

Because of its sensitivity to minor variations in radiographic density and its ability to eliminate overlapping because of the cross-sectional display, computed tomography (CT) of the skeletal system may yield valuable information that may not be apparent on plain film or radionclide examination of bone lesions. The authors present five case illustrations in which CT examination of bone was particularly helpful in the evaluation of the patient.

Computed tomographic scanning in children

Computed tomographic scanning (CT) has been effectively utilized in evaluating the pediatric patient. Our experience with CT of the chest and abdomen in 19 patients has been described. The advantages offered by CT include: a unique anatomic display, the lack of morbidity, and an acceptable radiation dosage. Few technical disadvantages exist. Further application of this unique technique can be predicted.

Computerized tomography and surgical treatment in intracranial suppuration. Report of 30 consecutive unselected cases of brain abscess and subdural empyema

The authors report their experience with 30 cases of intracranial suppuration: 23 with brain abscess and seven with subdural empyema. All of the cases were diagnosed by means of computerized tomography and enhancement with intravenous contrast material. Most of the patients were treated by single or repeated aspiration through burr holes.

Computerized cranial tomography and radionuclide imaging in the detection of intracranial mass lesions

Computerized cranial tomography (CCT) and radionuclide imaging (RI) of the brain are both accurate techniques for detecting intracranial mass lesions. CCT is superior in detecting low-grade gliomas, cystic lesions, parasellar tumors, and brain stem lesions. Overall, CCT detection rates are slightly higher than those with RI, but the use of iodinated contrast media with CCT increases the risk of this examination. There is a significant difference in the generally binary (positive/negative) type of information offered by RI and the more specific information offered by CCT about the pathologic nature of a lesion and its precise location. In the evaluation of patients with suspected intracranial mass lesions, CCT is generally the preferable initial diagnostic test. However, RI may still serve as a satisfactory screening examination in certain well-defined clinical situations.

Impact of computerised axial tomography of the management of posterior fossa tumours in childhood

Computerised axial tomography (CAT) has profoundly altered the management of most children with posterior fossa tumours. Fifty such children were operated on from October 1973 to December 1975, 20 of whom were explored after investigation by CAT only. Most recent experience suggests that CAT need by the only investigation in the majority of children suspected of having an expanding lesion in the posterior fossa.

The evolving role of computerized tomography in radiation oncology

The development and application of computerized tomography of the body have important implications in the diagnosis of tumors and in the planning of the radiotherapy treatment of malignancies because the modality provedes: a) an exact contour of transverse sections of the body; b) distinct representation of anatomic internal structures; c) ability to diagnose the presence and extent of tumor involvement of internal organs; d) opportunity to obtain, quantitatively, the "density" (x-ray absorption) of the anatomical structures in the sections; e) capability to develop isodose curves with inhomogeneity corrections; and f) ability to follow the response of a tumor to treatment, non-invasively. Although the diagnostic efficacy of computerized tomography of tumors, relative to other diagnostic modalities, is still to be defined accurately and the exact role of this new method in radiotherapy treatment planning is still to be determined, computerized tomography appears to provide oncologists with a valuable adjunct in their management of tumor patients.

Computed tomography in the postoperative care of neurosurgical patients

By its ability to differentiate the densities of various intracranial tissues, computed tomography is an ideal tool to investigate the postoperative course and complications of neurosurgical patients. The most important immediate postoperative complications are intracerebral edema and epidural, subdural or intracerebral hematomas. The extent of surgical resection of neoplasms can also be studied easily by CT. The method of investigation and representative cases are described.

Computed tomography of the abdomen: initial experience

Computed tomography has provided a new dimension in the roentgenologic evaluation of the abdomen. Normal structures not visible on conventional examinations are clearly identified. Abnormalities are recognized by their alterations in anatomic form or by their effect on tissue absorption values. Our early experience suggests that in the abdomen computed tomography will be most valuable in detecting lesions in those sites least accessible to conventional roentgenographic methods such as the liver, spleen, pancreas and retroperitoneum.

Calibration and response of an EMI scanner

Computed tomography provides a measurement of the linear absorption coefficient of material in vivo. The precision and accuracy of the measurements of this parameter made by the EMI scanner have been investigated at all three recommended voltage settings of the machine. The relationship between the EMI number and the linear absorption coefficient was found to be linear despite the polychromatic nature of the X-ray beam. The spatial resolution of the machine and the response to materials at different depths within the section have also been investigated.