Computed tomography assessment of sacroiliac screw placement relative to the first sacral neuroforamen

The radiographic interpretation of sacroiliac screws relative to the S1 neuroforamen is difficult for orthopedic surgeons and radiologists. Computed tomography (CT) with axial images alone or combined with multiplanar reconstructions are often used to assess screw position. The reliability, reproducibility, and accuracy of orthopedist and radiologist interpretations of axial CT images with and without multiplanar reconstructions was determined using 24 cadaveric hemipelves with known sacroiliac screw position. Interobserver reliability of determining screw position was fair for orthopedists and slight for radiologists regardless of imaging modality or screw composition. Intraobserver reproducibility was moderate for orthopedists regardless of imaging modality or screw type. Reproducibility among radiologists was moderate using axial images of titanium screws and substantial with addition of multiplanar reconstructions. Overall accuracy was similar for orthopedists and radiologists. CT images with multiplanar reconstructions improve accuracy in determining sacroiliac screw position, but not significantly. Current imaging modalities are limited by large inaccuracies and by interobserver and intraobserver variation.

Severity of coronary artery calcification by electron beam computed tomography predicts silent myocardial ischemia

BACKGROUND

Detection of subclinical coronary artery disease (CAD) before the development of life-threatening cardiac complications has great potential clinical relevance. Electron beam computed tomography (EBCT) is currently the only noninvasive test that can detect CAD in all stages of its development and thus has the potential to be an excellent screening technique for identifying asymptomatic subjects with underlying myocardial ischemia.

METHODS AND RESULTS

Over 2.5 years, we prospectively studied 3895 generally asymptomatic subjects with EBCT, 411 of whom had stress myocardial perfusion tomography (SPECT) within a close (median, 17 days) time period. SPECT and exercise treadmill results were compared with the coronary artery calcium score (CACS) as assessed by EBCT. The total CACS identified a population at high risk for having myocardial ischemia by SPECT although only a minority of subjects (22%) with an abnormal EBCT had an abnormal SPECT. No subject with CACS <10 had an abnormal SPECT compared with 2.6% of those with scores from 11 to 100, 11.3% of those with scores from 101 to 399, and 46% of those with scores >/=400 (P<0.0001). CACS predicted an abnormal SPECT regardless of subject age or sex.

CONCLUSIONS

CACS identifies a high-risk group of asymptomatic subjects who have clinically important silent myocardial ischemia. Our results support the role of EBCT as the initial screening tool for identifying individuals at various stages of CAD development for whom therapeutic decision making may differ considerably.

Imaging assessment of sacroiliac screw placement relative to the neuroforamen

STUDY DESIGN

Twenty-four cannulated sacroiliac screws were placed bilaterally into 12 cadaveric pelvi (12 titanium screws and 12 stainless-steel screws) and were imaged using conventional and multiplanar reconstructed computed tomography.

OBJECTIVES

To determine whether sacroiliac screw position assessment relative to the neuroforamen is enhanced by: 1) computed tomography using multiplanar reconstructions and 2) the use of titanium screws rather than stainless-steel screws.

SUMMARY OF BACKGROUND DATA

To the authors' knowledge, there have been no prior studies demonstrating the accuracy of multiplanar computed tomography compared with that of conventional (axial) tomography in determining the position of sacroiliac screws relative to the neuroforamen. Although titanium screws have been shown to have less scatter than stainless-steel screws, the effect of alloy composition on the radiographic accuracy of interpreting the screw position relative to the sacral neuroforamen is unknown.

METHODS

Screws were deliberately placed into: position A, in which the screw did not violate the neuroforamen; position B, in which the threads of the screw came within 3 mm of the neuroforamen; and position C, in which the screw clearly was nearly centered in the neuroforamen. The degrees of accuracy in assessing screw position relative to the neuroforamen using conventional (axial) images and using multiplanar reconstructed images were compared.

RESULTS

The axial images were accurate in determining screw position relative to the neuroforamen in 50% of cases in which titanium screws were used and in 42% of cases in which stainless-steel screws were used. The corresponding values for multiplanar reconstructions were 92% for cases in which titanium screws were used and 67% for cases in which stainless-steel screws were used. The accuracy of multiplanar reconstructions was statistically better than that of axial images (P < 0.05). Metallic scatter was increased in stainless-steel screws.

CONCLUSIONS

The results of this study suggest that the use of computed tomography with multiplanar reconstruction improves accuracy in determining sacroiliac screw position relative to the neuroforamen. The assessment of screw position may be facilitated using titanium screws.

CT reconstruction of an unusual chronic posttraumatic aneurysm of the thoracic aorta

Chronic traumatic aneurysm of the thoracic aorta is an unusual occurrence. Previously, arteriography was performed on all patients seen in our institution with this entity to allow confirmation of the diagnosis and anatomic delineation for operation. A case of chronic traumatic aneurysm of the distal descending aorta discovered on a routine chest roentgenogram and evaluated with chest computed tomographic scanning with three-dimensional reconstruction is presented. It is our belief that not all thoracic aneurysms require arteriography, and improved methods of computed tomographic scanning allow adequate diagnosis and anatomic delineation with decreased morbidity and cost.

Eddy current correction in volume-localized MR spectroscopy

The quality of volume-localized magnetic resonance spectroscopy is affected by eddy currents caused by gradient switching. Eddy currents can be reduced with improved gradient systems; however, it has been suggested that the distortion due to eddy currents can be compensated for during postprocessing with a single-frequency reference signal. The authors propose modifying current techniques for acquiring the single-frequency reference signal by using relaxation weighting to reduce interference from components that cannot be eliminated by digital filtering alone. Additional sequences with T1 or T2 weighting for reference signal acquisition are shown to have the same eddy current characteristics as the original signal without relaxation weighting. The authors also studied a new eddy current correction method that does not require a single-frequency reference signal. This method uses two free induction decays (FIDs) collected from the same volume with two sequences with opposite gradients. Phase errors caused by eddy currents are opposite in these two FIDs and can be canceled completely by combining the FIDs. These methods were tested in a phantom. Eddy current distortions were corrected, allowing quantitative measurement of structures such as the -CH = CH- component, which is otherwise undetectable.

Changes in intervertebral disc cross-sectional area with bed rest and space flight

STUDY DESIGN

We measured the cross-sectional area of the intervertebral discs of normal volunteers after an overnight rest; before, during, and after 5 or 17 weeks of bed rest; and before and after 8 days of weightlessness.

OBJECTIVES

This study sought to determine the degree of expansion of the lumbar discs resulting from bed rest and space flight.

SUMMARY OF BACKGROUND DATA

Weightlessness and bed rest, an analog for weightlessness, reduce the mechanical loading on the musculoskeletal system. When unloaded, intervertebral discs will expand, increasing the nutritional diffusion distance and altering the mechanical properties of the spine.

METHODS

Magnetic resonance imaging was used to measure the cross-sectional area and transverse relaxation time (T2) of the intervertebral discs.

RESULTS

Overnight or longer bed rest causes expansion of the disc area, which reaches an equilibrium value of about 22% (range 10-40%) above baseline within 4 days. Increases in disc area were associated with modest increases in disc T2. During bed rest, disc height increased approximately 1 mm, about one-half of previous estimates based on body height measurements. After 5 weeks of bed rest, disc area returned to baseline within a few days of ambulation, whereas after 17 weeks, disc area remained above baseline 6 weeks after reambulation. After 8 days of weightlessness, T2, disc area, and lumbar length were not significantly different from baseline values 24 hours after landing.

CONCLUSIONS

Significant adaptive changes in the intervertebral discs can be expected during weightlessness. These changes, which are rapidly reversible after short-duration flights, may be an important factor during and after long-duration missions.

A technique for flow-enhanced magnetic resonance angiography of the lower extremities

A two-dimensional, flow-enhanced gradient echo pulse sequence for nuclear magnetic resonance angiography is described. It employs interleaved, presaturated slices to acquire data efficiently on imagers which favor interleaved acquisition over sequential acquisition for multislice imaging. It is useful on any imagers when the effective TR is extended to enhance the sensitivity to slow flow. The technique was applied to the region from aortic bifurcation to the iliac bifurcations of three normal volunteers. The right and left common iliac arteries and veins, the separation of the external and internal iliac arteries, and secondary branches were clearly depicted.

Assessment of tissue iron overload by nuclear magnetic resonance imaging

PURPOSE

The ability of stored intracellular iron to enhance magnetic susceptibility forms the basis by which tissue iron can be detected by nuclear magnetic resonance (NMR) imaging. We used this technique to assess myocardial, spleen, and liver iron content in patients with known or suspected iron overload disorders.

PATIENTS AND METHODS

Spin echo NMR images were obtained in 30 patients; 20 had chronic anemias treated by multiple blood transfusions, five had idiopathic hemochromatosis, and five had non-hemochromatotic liver disease with elevated serum ferritin levels and no stainable iron on liver biopsy. The acquisition of oblique images through the short axis of the left ventricle permitted assessment of left ventricular function, while demonstrating the liver and spleen on the same image. Iron content was assessed using a signal intensity ratio of organ (spleen, liver, or myocardium) to skeletal muscle.

RESULTS

In patients with multiple blood transfusions, iron content was highest in liver, followed by the spleen. Significant iron overload was detected in the myocardium of only one patient. Left ventricular systolic wall thickening was normal in patients receiving multiple blood transfusions. Two patients with treated idiopathic hemochromatosis had normal signal intensity ratios, and three untreated patients had evidence of significant deposits of iron in the liver and spleen as indicated by a reduction in signal intensity ratios (0.2 +/- 0.01 and 0.9 +/- 0.01, respectively). Five patients with non-hemochromatotic liver disease and high serum ferritin levels had normal signal intensity ratios by NMR imaging.

CONCLUSION

NMR imaging is a useful method of detecting tissue iron and distinguishing disease due to iron overload. Myocardial iron deposition is a late event, occurring after accumulation of iron in the spleen and liver.

Balloon dilation of unoperated coarctation of the aorta: short- and intermediate-term results

Balloon dilation is effective in the immediate relief of obstruction due to unoperated coarctation of the aorta. However, the long-term benefits and complications of this procedure have not been established. Thirty-three patients underwent balloon dilation of unoperated coarctation using a percutaneous technique from November 1983 to December 1985. High quality biplane angiography was performed before and after dilation. Follow-up was obtained in 20 patients from 6 to 31 months following dilation. Angiography was performed at follow-up in 10, nuclear magnetic resonance (NMR) imaging in 10 and both NMR imaging and angiography in 3. Balloon dilation was successful in 31 of the 33 patients with a decrease in average systolic pressure gradient from 46 to 8 mm Hg. There was no significant change in gradient on follow-up physical examination and at recatheterization in 10 patients. In addition, there was no evidence of restenosis on follow-up angiography and NMR imaging. In two patients, a small aneurysm formed at the site of balloon dilation. Balloon dilation of unoperated coarctation is effective, providing lasting relief of coarctation gradient and no evidence of restenosis. However, because of the uncertain natural history of aneurysms after dilation, this procedure should be considered investigational until further follow-up on patients with and without an aneurysm is available.

Ultrasonic demonstration of ectopic ureterocele

The gray scale ultrasound findings in two children with ectopic ureterocele are presented and correlated with traditional radiographic findings. In one case, the diagnosis was made in utero, utilizing ultrasound. The examination is noninvasive and performed quickly, and it may be able to replace the intravenous pyelogram in the initial evaluation of patients suspected of having such congenital anomalies. Retrograde cystography will still be necessary to detect vesicoureteral reflux.