Image fusion of CT and MRI for the visualization of the auditory and vestibular system

The aim of this study was to perform a realistic visualization of the auditory and vestibular system using volume data sets from high-resolution computed tomography (HR-CT) and high-resolution magnetic resonance imaging (HR-MRI). - In 10 patients with conductive and/or sensorineural hearing loss, vertigo and tinnitus, HR-CT and HR-MRI of the petrous bone were performed consecutively. CT was performed with a 16-slice computed tomography scanner using a high spatial resolution. MRI was performed with a 3.0 Tesla scanner using a three-dimensional-constructive interference in steady state (3D-CISS) gradient-echo, and T2-weighted, unenhanced and gadolinium (GD)-enhanced T1-weighted turbo spin-echo sequences. The middle ear structures were interactively segmented and visualized with a color-coded shaded-surface rendering method using the HR-CT volume data sets. The inner ear structures were interactively segmented and visualized with a color-coded shaded-surface rendering method using the high-resolution 3D-CISS MRI volume data sets. Finally, both shaded-surface rendered models were superimposed semi-automatically using a commercial available software program to visualize the auditory and vestibular system. - The representation of the middle and inner ear structures with image fusion of HR-CT and HR-MRI takes advantage of both the high bony contrast of HR-CT and the high soft tissue contrast discrimination and sensitivity to fluids of HR-MRI, as well as the high spatial resolution of both modalities. In comparison to the fused axial CT/MRI, the images of 3D CT/MRI fusion facilitates a clear representation and better spatial orientation. - The middle and inner ear consists of bony structures, soft tissue structures and fluid-filled spaces. For this reason, the image fusion of volume data sets from HR-CT and HR-MRI allowed an optimized and realistic visualization of the auditory and vestibular system.

Beobachtung und Kontrolle von Fixiervorgängen in Leberpräparaten mittels MRT und MRS

PURPOSE

The purpose of this study was to observe the process of fixation in liver specimens non-invasively by means of magnetic resonance. The fixation process of several formaldehyde-containing solutions was monitored with MRI and MRS at two different temperatures.

MATERIALS AND METHODS

Liver specimens were conserved in aqueous fixative solutions containing formaldehyde concentrations of 0.7, 1.8, 4 and 7.2 % and at different temperatures of 5 degrees C and 20 degrees C. MRI was performed with T1-, T2- and PD-weighted TSE sequences, a 2D FLASH-sequence with and without magnetization transfer, and a FISP 3D-sequence on a clinical 1.5 Tesla MR whole-body unit, and MRS with (1)H-spectroscopic methods (STEAM-sequence) on a 3 Tesla MR whole-body unit.

RESULTS

The diffusion of formaldehyde into the tissue was best identified on PD- and T1-weighted images as a band under the liver surface with increasing thickness, penetrating especially fast during the first three days. Spectroscopic measurements revealed the rising formaldehyde concentration in the inner part of the organs. Temperature had no significant influence on the velocity of immersing, but cooling conditions produced less gas-filled caverns due to reduced undesired decomposition processes.

CONCLUSION

The spatial and temporal process of ongoing fixation in the liver can be monitored by MRI. MRS confirms a rising concentration of formaldehyde during ongoing fixation.

MR Visualization of the Inner Ear Structures: Comparison of 1.5 Tesla and 3 Tesla Images

AIM OF THE STUDY

To compare high resolution MRI examinations of inner ear structures at 1.5 T and at 3 T.

METHOD

Temporal bones were measured bilaterally in 3 healthy volunteers in a 1.5 T and in a 3 T MR-scanner using the respective one channel head coil (quadrature detection) of the manufacturer. The same steady-state gradient echo sequence (3D-CISS) was employed at a voxel size of 0.4 x 0.4 x 0.4 mm(3). The signal-to-noise ratio (SNR) was determined quantitatively.

RESULTS

An SNR of 8 could be achieved for the measurements at 3 T in 7:37 min. The SNR at 3 T was, on average, a factor of 1.34 higher than that at 1.5 T despite the fact that the excitation angle had to be drastically reduced (alpha = 42 degrees instead of alpha = 70 degrees at 1.5 T) due to the limit of the specific absorption rate (SAR).

DISCUSSION

The MR representation of the inner ear is clearly improved at 3 T. To obtain the same SNR at 1.5 T approximately the double measuring time would be required, connected with reduced patient comfort and an increased risk for a displacement of the head during the high resolution measurement.

Systematik der Artefakte metallischer Gefäßprothesen (Stents) in der MRT

PURPOSE

Imaging artifacts in magnetic resonance tomography (MRT) caused by metallic vascular implants (stents) were characterized systematically in dependence on the material and the construction of the implants as well as with respect to different measurement protocols and for different static field strength B (0).

METHODS

Twelve stents, different in material (stainless steel, nitinol, Co-alloy) and/or construction, were examined at B (0) = 0.2 T and 1.0 T with two 2D gradient echo (GE) sequences (TE = 4 and 10 ms), one 3D GE sequence and one spin echo (SE) sequence. The stents were put into water with Gd-DTPA contrast agent. The dependence on the orientation was analyzed for the 9 possibilities of an orthogonal alignment of the stent axis, the direction of B (0), the slice, the read out, and the phase encoding direction. Special interest was given to the visibility of the stent lumen at forced rf excitation, as well as to the influence of broken struts on the signal obtained.

RESULTS

For the examined stents GE technique showed, due to spin dephasing regions a total signal loss ranging up to 8 mm away from the stent mashes. The value depends on the stent material, the stent orientation in the scanner and grows with voxel size, echo time and B (0). In SE technique dephasing artifacts vanish and wrong spatial encoding gets visible, rf shielding is more pronounced. The visibility of the stent lumen ranges from nearly unperturbed down to a complete signal loss. An improvement is possible using enlarged flip angles. Broken struts can not be imaged significantly.

DISCUSSION

The MR representation of metallic stents commercially available at the time, especially of nitionol stents, can be optimized with a suitable adaptation of the imaging parameters. However, a profound improvement can only be expected from new stent material and design.

[Characterization of motion artifacts in multi-slice spiral CT]

PURPOSE

Motion artifacts in multi-slice spiral CT (MSCT) resulting from object motion in and against the table feed direction (z-direction) are examined using a spherical phantom. For image interpretation of complex anatomic structures, qualitative reference points are, also applicable to selected, which are ECG-gated cardiac imaging. In this case the motion of the coronary vessels in phase with the cardiac contraction must be considered.

METHODS

Measurements are obtained with a multi-slice spiral CT with a rotation time of 500 ms for 4 x 1.0 mm and 2 x 0.5 mm collimation. The phantom consists of an acrylic glass body with imbedded glass beads of 1, 2, and 3 mm diameter. The object motion is sinusoidal with an amplitude of 5 mm and frequencies of 60/min and 90/min. Compensation of the table feed by object motion is examined as a special case.

RESULTS

Small parameter changes can induce a strikingly different image quality, and the moving objects emerge in different slices. Depending on the phase of the movement with respect to the CT scan, objects up to a size of 3 mm can vanish completely or appear hyperintense in the image. The model investigated is also applicable to ECG-gated cardiac imaging for the detection of stenosis. It can explain variations in the reproducibility and absolute score values of the calcium scoring.

CONCLUSION

The presented considerations and results must be taken into account in image interpretation with possible object motion in the z-direction. Variations in the determination of the degree of stenosis or in calcium score measurements can be explained by different vessel motion during the diastolic heart phase.

Aggressive behavior of papillary microcarcinoma in a patient with Graves' disease initially presenting as cystic neck mass

Prognosis of papillary carcinoma of the thyroid associated with Graves' disease is controversial; nevertheless, tumors smaller than 1 cm (microcarcinoma) are usually considered to render a good prognosis. We describe a patient with Graves' disease who developed a lateral cystic neck mass that was later confirmed to be a metastatic lymph node from papillary thyroid microcarcinoma. Contrary to having a good prognosis with a microcarcinoma, our patient developed bilateral lung metastases. The possible role of thyroid stimulating immunoglobulins in the aggressive course of the tumor is discussed.

Amyloidotic muscle pseudohypertrophy: case report

The authors report one case of amyloidosis associated with muscular pseudohypertrophy in a 46-year-old woman, who developed weakness, macroglossia and muscle hypertrophy associated with primary systemic amyloidosis. Electromyography showed a myopathic pattern and bilateral carpal tunnel syndrome. The muscle biopsy presented with a type I and II fiber hypertrophy and infiltration of amyloid material in the interstitious space and artery walls. She underwent bone marrow transplantation with stabilization and subjective improvement of the clinical picture.

Efficacy of ultrasound-guided fine-needle aspiration biopsy in the diagnosis of complex thyroid nodules

Cystic thyroid nodules are considered to be one of the major causes of nondiagnostic and false-negative results on conventional fine-needle aspiration biopsy, thus limiting the potential of this method for the evaluation of complex (solid-cystic) thyroid nodules. Although ultrasound-guided fine-needle aspiration biopsy has emerged as a highly effective diagnostic method for the assessment of nonpalpable and difficult to palpate nodules, its role in complex nodules has not yet been carefully evaluated. In this study, we report the efficacy of ultrasound-guided fine-needle aspiration biopsy in 124 complex nodules in 113 patients. This method proved to be highly effective, yielding a satisfactory specimen for cytological evaluation in 94% of the nodules, suggesting that it is an excellent modality for the evaluation of complex nodules and also for the reevaluation of those nodules with a nondiagnostic result on conventional fine-needle aspiration biopsy.

Relationship between nonphenacetin combined analgesics and nephropathy: a review. Ad Hoc Committee of the International Study Group on Analgesics and Nephropathy

BACKGROUND

The debate on the association between nonphenacetin-containing combined analgesics and renal disease has lasted for several years.

METHOD

A peer review committee of scientists, selected jointly by the regulatory authorities of Germany, Switzerland, and Austria and the pharmaceutical industry was asked to critically review data on the relationship between nonphenacetin combined analgesics and nephropathy.

RESULTS

The committee regarded epidemiologic evidence on nonphenacetin combined analgesics as inconclusive because of sparse information and substantial methodological problems. The committee also noted that a diagnosis of analgesic-associated nephropathy (AAN) in clinical practice usually depends on information about exposure before or in the early stages of the disease and is seldom accompanied by specific histologic evidence. The morphologic finding of papillary calcification can arise from other conditions and is not specific for AAN. For these reasons, the identification criteria for AAN should be reappraised with scientific methods to validate the diagnostic procedure. In the limited amount of experimental pharmacological data in humans and animals, the committee found no convincing evidence to confirm or refute the hypothesis that nonphenacetin combined analgesics are more nephrotoxic than single formulations. For caffeine taken with combined analgesics, the currently available information is not sufficient to postulate a harmful toxicological effect.

CONCLUSION

The committee's two main conclusions were that sufficient evidence is absent to associate nonphenacetin combined analgesics with nephropathy and that new studies should be done to provide appropriate data for resolving the question.

Concomitant presentation of Hashimoto's thyroiditis and maltoma of the thyroid in a twenty-year-old man with a rapidly growing mass in the neck

We report an uncommon case of a 20-year-old man, who noted a painless, growing mass in his neck, which appeared in a weekend, associated with moderate dysphagia and weakness. Laboratory examination revealed an elevated serum thyrotropin of 25 mU/L, normal serum triiodothyronine and thyroxine levels, and high titers of antithyroglobulin and antithyroid peroxidase antibodies. The neck lesion showed a depressed iodine uptake in the left thyroid lobe, which had an asymmetrical pseudocystic pattern associated with poor vascularization in the ultrasound scan. Cytologic examination showed a lymphocyte thyroiditis in association with lymphoma of large cell arising from mucosa-associated lymphoid tissue (MALT-lymphoma or maltoma). The patient underwent a left thyroid lobectomy while being treated with levothyroxine for Hashimoto's thyroiditis, and the surgical treatment was further complemented with chemotherapy using fludarabine. The histologic examination confirmed the cytologic findings and the immunohistochemistry showed a B-cell type maltoma. Additional investigation provided no evidence of disease in other tissues. The clinical course has been favorable in the first 2 years of follow-up, with no evidence of local or systemic recurrence of the disease.

First experimental evidence for chaos-assisted tunneling in a microwave annular billiard

We report on first experimental signatures for chaos-assisted tunneling in a two-dimensional annular billiard. Measurements of microwave spectra from a superconducting cavity with high frequency resolution are combined with electromagnetic field distributions experimentally determined from a normal conducting twin cavity with high spatial resolution to resolve eigenmodes with properly identified quantum numbers. Distributions of quasidoublet splittings serve as basic observables for the tunneling between whispering gallery-type modes localized to congruent, but distinct tori which are coupled weakly to irregular eigenstates associated with the chaotic region in phase space.

Molecular analyses of the vasopressin type 2 receptor and aquaporin-2 genes in Brazilian kindreds with nephrogenic diabetes insipidus

Nephrogenic diabetes insipidus (NDI) is associated with germline mutations in two genes: vasopressin receptor type 2 (V2(R)) in X-linked NDI, and the water channel aquaporin-2, in autosomal-recessive disease. Genetic heterogeneity is further emphasized by reports of phenotypically abnormal individuals with normal structural genes. We analyzed both genes in five Brazilian families and the aquaporin-2 gene in two Swedish families with clinical and laboratory diagnosis of NDI, by a combination of denaturing gradient gel electrophoresis (DGGE) and direct DNA sequencing. A novel polymorphism in the aquaporin-2 gene (S167S), but no disease-associated mutations in any tested individual from all seven families, was detected. In two Brazilian families, frameshift mutations were detected in the V2(R) gene: one leading to a premature stop after codon 36 and the other to a longer peptide (462 aa instead of the 373 aa wild-type protein). In two other Brazilian families, probable disease-associated missense mutations were detected: an alanine to proline at codon 163 (A163P) and an asparagine to aspartic acid at codon 85 (D85N). In one Brazilian family, both genes were structurally normal and the aquaporin-2 gene was also normal in the two Swedish kindreds. This report further extends the mutational spectrum of NDI and suggests that there are other mutational or epigenetic events inactivating the two known genes or even novel genes that underlie NDI.