SPIR MRI in spinal diseases

Structured low-rank reconstruction for navigator-free water/fat separated multi-shot diffusion-weighted EPI

PURPOSE

Multi-shot diffusion-weighted EPI allows an increase in image resolution and reduced geometric distortions and can be combined with chemical-shift encoding (Dixon) to separate water/fat signals. However, such approaches suffer from physiological motion-induced shot-to-shot phase variations. In this work, a structured low-rank-based navigator-free algorithm is proposed to address the challenge of simultaneously separating water/fat signals and correcting for physiological motion-induced shot-to-shot phase variations in multi-shot EPI-based diffusion-weighted MRI.

THEORY AND METHODS

We propose an iterative, model-based reconstruction pipeline that applies structured low-rank regularization to estimate and eliminate the shot-to-shot phase variations in a data-driven way, while separating water/fat images. The algorithm is tested in different anatomies, including head-neck, knee, brain, and prostate. The performance is validated in simulations and in-vivo experiments in comparison to existing approaches.

RESULTS

In-vivo experiments and simulations demonstrated the effectiveness of the proposed algorithm compared to extra-navigated and an alternative self-navigation approach. The proposed algorithm demonstrates the capability to reconstruct in the multi-shot/Dixon hybrid space domain under-sampled datasets, using the same number of acquired EPI shots compared to conventional fat-suppression techniques but eliminating fat signals through chemical-shift encoding. In addition, partial Fourier reconstruction can also be achieved by using the concept of virtual conjugate coils in conjunction with the proposed algorithm.

CONCLUSION

The proposed algorithm effectively eliminates the shot-to-shot phase variations and separates water/fat images, making it a promising solution for future DWI on different anatomies.

Water/fat separation for self-navigated diffusion-weighted multishot echo-planar imaging

The purpose of this study was to develop a self-navigation strategy to improve scan efficiency and image quality of water/fat-separated, diffusion-weighted multishot echo-planar imaging (ms-EPI). This is accomplished by acquiring chemical shift-encoded diffusion-weighted data and using an appropriate water-fat and diffusion-encoded signal model to enable reconstruction directly from k-space data. Multishot EPI provides reduced geometric distortion and improved signal-to-noise ratio in diffusion-weighted imaging compared with single-shot approaches. Multishot acquisitions require corrections for physiological motion-induced shot-to-shot phase errors using either extra navigators or self-navigation principles. In addition, proper fat suppression is important, especially in regions with large B₀ inhomogeneity. This makes the use of chemical shift encoding attractive. However, when combined with ms-EPI, shot-to-shot phase navigation can be challenging because of the spatial displacement of fat signals along the phase-encoding direction. In this work, a new model-based, self-navigated water/fat separation reconstruction algorithm is proposed. Experiments in legs and in the head-neck region of 10 subjects were performed to validate the algorithm. The results are compared with an image-based, two-dimensional (2D) navigated water/fat separation approach for ms-EPI and with a conventional fat saturation approach. Compared with the 2D navigated method, the use of self-navigation reduced the shot duration time by 30%-35%. The proposed algorithm provided improved diffusion-weighted water images in both leg and head-neck regions compared with the 2D navigator-based approach. The proposed algorithm also produced better fat suppression compared with the conventional fat saturation technique in the B₀ inhomogeneous regions. In conclusion, the proposed self-navigated reconstruction algorithm can produce superior water-only diffusion-weighted EPI images with less artefacts compared with the existing methods.

Regularized joint water-fat separation with B0 map estimation in image space for 2D-navigated interleaved EPI based diffusion MRI

Purpose

To develop a new water–fat separation and B₀ estimation algorithm to effectively suppress the multiple resonances of fat signal in EPI. This is especially relevant for DWI where fat is often a confounding factor.

Methods

Water–fat separation based on chemical‐shift encoding enables robust fat suppression in routine MRI. However, for EPI the different chemical‐shift displacements of the multiple fat resonances along the phase‐encoding direction can be problematic for conventional separation algorithms. This work proposes a suitable model approximation for EPI under B₀ and fat off‐resonance effects, providing a feasible multi‐peak water–fat separation algorithm. Simulations were performed to validate the algorithm. In vivo validation was performed in 6 volunteers, acquiring spin‐echo EPI images in the leg (B₀ homogeneous) and head‐neck (B₀ inhomogeneous) regions, using a TE‐shifted interleaved EPI sequence with/without diffusion sensitization. The results are numerically and statistically compared with voxel‐independent water–fat separation and fat saturation techniques to demonstrate the performance of the proposed algorithm.

Results

The reference separation algorithm without the proposed spatial shift correction caused water–fat ambiguities in simulations and in vivo experiments. Some spectrally selective fat saturation approaches also failed to suppress fat in regions with severe B₀ inhomogeneities. The proposed algorithm was able to achieve improved fat suppression for DWI data and ADC maps in the head–neck and leg regions.

Conclusion

The proposed algorithm shows improved suppression of the multi‐peak fat components in multi‐shot interleaved EPI applications compared to the conventional fat saturation approaches and separation algorithms.

Use of Multiplied, Added, Subtracted and/or FiTted Inversion Recovery (MASTIR) pulse sequences

The group of Multiplied, Added, Subtracted and/or fiTted Inversion Recovery (MASTIR) pulse sequences in which usually two or more inversion recovery (IR) images of different types are combined is described, and uses for this type of sequence are outlined. IR sequences of different types can be multiplied, added, subtracted, and/or fitted together to produce variants of the MASTIR sequence. The sequences provide a range of options for increasing image contrast, demonstrating specific tissues and fluids of interest, and suppressing unwanted signals. A formalism using the concept of pulse sequences as tissue property filters is used to explain the signal, contrast and weighting of the pulse sequences with both univariate and multivariate filter models. Subtraction of one magnitude reconstructed IR image from another with a shorter TI can produce very high T₁ dependent positive contrast from small increases in T₁. The reverse subtracted IR sequence can provide high positive contrast enhancement with gadolinium chelates and iron deposition which decrease T₁. Additional contrast to that arising from increases in T₁ can be produced by supplementing this with contrast arising from concurrent increases in ρ_m and T₂, as well as increases or decreases in diffusion using subtraction IR with echo subtraction and/or diffusion subtraction. Phase images may show 180º differences as a result of rotating into the transverse plane both positive and negative longitudinal magnetization. Phase images with contrast arising in this way, or other ways, can be multiplied by magnitude IR images to increase the contrast of the latter. Magnetization Transfer (MT) and susceptibility can be used with IR sequences to improve contrast. Selective images of white and brown adipose tissue lipid and water components can be produced using different TIs and in and out-of-phase TEs. Selective images of ultrashort and short T₂ tissue components can be produced by nulling long T₂ tissue components with an inversion pulse and subtraction of images with longer TEs from images with ultrashort TEs. The Double Echo Sliding IR (DESIRE) sequence provides images with a wide range of TIs from which it is possible to choose values of TI to achieve particular types of tissue and/or fluid contrast (e.g., for subtraction with different TIs, as described above, and for long T₂ tissue signal nulling with UTE sequences). Unwanted tissue and fluid signals can be suppressed by addition and subtraction of phase-sensitive (ps) and magnitude reconstructed images. The sequence also offers options for synergistic use of the changes in blood and tissue ρ_m, T₁, T₂/T₂*, D* and perfusion that can be seen with fMRI of the brain. In-vivo and ex-vivo illustrative examples of normal brain, cartilage, multiple sclerosis, Alzheimer's disease, and peripheral nerve imaged with different forms of the MASTIR sequence are included.

MR imaging of acute cervical spinal ligamentous and soft tissue trauma

The increasing availability of magnetic resonance imaging (MRI) and the high sensitivity of MRI for soft tissue injury are resulting in the increased use of MRI for the evaluation of acute trauma. As cervical spine injury can have a devastating consequence, MRI is being more commonly used to evaluate cervical spine injury in the acute setting, necessitating emergent interpretation by the on-call radiologist. Unless one is formally trained in a trauma center, the MRI findings of soft tissue and ligamentous cervical spine injury may not be fully appreciated. The goal of this pictorial review is to familiarize the reader with some of the more common soft tissue, vascular, and ligamentous injuries seen on MRI of the cervical spine in the emergent setting.

Diagnostic abilities of magnetic resonance imaging in traumatic injury to the posterior ligamentous complex: the effect of years in training

BACKGROUND CONTEXT

The integrity of the posterior ligamentous complex (PLC) has been proposed to be an integral aspect in the treatment algorithm for spinal trauma. Magnetic resonance imaging (MRI) has been reported as the ideal tool to determine the integrity of the PLC. The ability to assess disruption of the PLC by reviewers of differing levels of training has not been described. In addition, the MRI sequence most suggestive of injury for each component of the PLC has not been clearly determined.

PURPOSE

This study was designed to determine the ability of reviewers with differing levels of training (fellowship-trained spine surgeon, fellowship-trained musculoskeletal radiologist, senior orthopedic surgery resident, and junior orthopedic surgery resident) to accurately interpret the results of MRI. The secondary purpose was to evaluate the MRI sequence that was most indicative of injury to the components of the PLC.

STUDY DESIGN

This is a prospective radiological study comparing reviewers of MRI to determine integrity of the PLC components using intraoperative notation as the gold standard for integrity.

PATIENT SAMPLE

Forty-five consecutive spinal trauma patients who underwent operative fixation after obtaining MRI.

OUTCOME MEASURES

No patient outcome measures were used.

METHODS

The sensitivity, specificity, and accuracy for each MRI reviewer in regard to MRI integrity were compared with the gold standard of intraoperative observation. In addition, the MRI sequence most suggestive of integrity of the PLC was noted by each reviewer for each component of the PLC.

RESULTS

Forty-five patients (29 men and 16 women) with traumatic spine injuries were enrolled in the study. The sensitivity and accuracy of the surgeon were 0.83 (0.66, 0.92) and 0.81 (0.70, 0.88), respectively. The sensitivity and accuracy of the attending spine surgeon were not statistically significantly different from the other reviewers (p value=.2317 and .2582). However, the specificity of the surgeon was statistically significantly higher than that of the other reviewers (p=.0043). In the cervical, thoracic, and lumbar spine, the reviewers reached a 93% agreement that the sagittal short-tau inversion recovery (STIR) sequences were most helpful in visualizing injury to the supraspinous ligament (SSL), interspinous ligament (ISL), ligamentum flavum (LF), and the cervical facet capsules. The reviewers attained a 95% agreement that visualization of injury to the lumbar facet capsules is most optimal in the T2 axial sequences.

CONCLUSIONS

The interpretation of traumatic MRI is very sensitive and accurate regardless of years of training of the observer. The attending-level spine surgeon was statistically more specific in the evaluation of injury MRIs. The fluid-weighted STIR sagittal sequences are most useful in determining injury to the SSL, ISL, LF, and cervical facets capsules. Lumbar facet capsules are best evaluated with axial T2 MRI. The evaluation of the PLC on MRI can be accurately and efficiently interpreted by physicians at multiple levels of training, thus providing a key imaging modality in determining stability and need for stabilization.

Whole-heart coronary magnetic resonance angiography at 3.0T using short-TR steady-state free precession, vastly undersampled isotropic projection reconstruction

PURPOSE

To evaluate the feasibility of improving 3.0T steady-state free precession (SSFP) whole-heart coronary magnetic resonance angiography (MRA) using short-TR (repetition time) VIPR (vastly undersampled isotropic projection reconstruction).

MATERIALS AND METHODS

SSFP is highly sensitive to field inhomogeneity. VIPR imaging uses nonselective radiofrequency pulses, allowing short TR and reduced banding artifacts, while achieving isotropic 3D resolution. Coronary artery imaging was performed in nine healthy volunteers using SSFP VIPR. TR was reduced to 3.0 msec with an isotropic spatial resolution of 1.3 x 1.3 x 1.3 mm(3). Image quality, vessel sharpness, and lengths of major coronary arteries were measured. Comparison between SSFP using Cartesian trajectory and SSFP using VIPR trajectory was performed in all volunteers.

RESULTS

Short-TR SSFP VIPR resulted in whole-heart images without any banding artifacts, leading to excellent coronary artery visualization. The average image quality score for VIPR-SSFP was 3.12 +/- 0.42 out of four while that for Cartesian SSFP was 0.92 +/- 0.61. A significant improvement (P < 0.05) in image quality was shown by Wilcoxon comparison. The visualized coronary artery lengths for VIPR-SSFP were: 10.13 +/- 0.79 cm for the left anterior descending artery (LAD), 7.90 +/- 0.91 cm for the left circumflex artery (LCX), 7.50 +/- 1.65 cm for the right coronary artery (RCA), and 1.84 +/- 0.23 cm for the left main artery (LM). The lengths statistics for Cartesian SSFP were 1.57 +/- 2.02 cm, 1.54 +/- 1.93 cm, 0.94 +/- 1.17 cm, 0.46 +/- 0.53 cm, respectively. The image sharpness was also increased from 0.61 +/- 0.13 (mm(-1)) in Cartesian-SSFP to 0.81 +/- 0.11 (mm(-1)) in VIPR-SSFP.

CONCLUSION

With VIPR trajectory the TR is substantially decreased, reducing the sensitivity of SSFP to field inhomogeneity and resulting in whole-heart images without banding artifacts at 3.0T. Image quality improved significantly over Cartesian sampling.

Using magnetic resonance imaging to accurately assess injury to the posterior ligamentous complex of the spine: a prospective comparison of the surgeon and radiologist

Object

Magnetic resonance imaging has been proposed as a powerful technique for assessing the integrity of the posterior ligamentous complex (PLC) in spinal trauma. Because MR imaging is often used to determine appropriate treatment, it is important to determine the accuracy and reliability of MR imaging in diagnosing PLC disruption. The purpose of this study is to compare the ability of the radiologist and surgeon to assess disruption of the PLC in the setting of acute cervical and thoracolumbar trauma using MR imaging.

Methods

The components of the PLC in 89 consecutive patients with cervical or thoracolumbar fractures following acute spinal trauma were evaluated using MR imaging by both a musculoskeletal radiologist and an independent spine surgeon and assessed intraoperatively under direct visualization by the treating surgeon. The MR imaging interpretations of the musculoskeletal radiologist and surgeon were compared with the intraoperative report for accuracy, sensitivity, specificity, and positive and negative predictive values. A comparison between the radiologist's and spine surgeon's accuracy of MR imaging interpretation was performed.

Results

The agreement between both the spine surgeon's and radiologist's MR imaging interpretation and the actual intraoperative findings was moderate for most components of the PLC. Overall, the MR imaging interpretation of the surgeon was more accurate than that of the radiologist. The interpretation of MR imaging by the surgeon had negative predictive value and sensitivity of up to 100%. However, the specificity of MR imaging for both the surgeon and radiologist was lower, ranging from 51.5 to 80.5%.

Conclusions

Comparison of the MR imaging interpretations between surgeon and radiologist indicates that the surgeon was more accurate for some PLC components. The relatively low positive predictive value and specificity for MR imaging in assessing PLC integrity suggests that both the surgeon and radiologist tend to overdiagnose PLC injury using MR imaging. This can lead to unnecessary surgeries if only MR imaging is used for treatment decision making.

Molecular MR imaging of melanoma angiogenesis with alphanubeta3-targeted paramagnetic nanoparticles

Neovascularization is a critical component in the progression of malignant melanoma. The objective of this study was to determine whether alpha(nu)beta(3)-targeted paramagnetic nanoparticles can detect and characterize sparse alpha(nu)beta integrin expression on neovasculature induced by nascent melanoma xenografts ( approximately 30 mm(3)) at 1.5T. Athymic nude mice bearing human melanoma tumors were intravenously injected with alpha(v)beta(3)-integrin-targeted paramagnetic nanoparticles, nontargeted paramagnetic nanoparticles, or alpha(v)beta(3)-targeted-nonparamagnetic nanoparticles 2 hr before they were injected with alpha(v)beta(3)-integrin-targeted paramagnetic nanoparticles (i.e., in vivo competitive blockade) and imaged with MRI. Contrast enhancement of neovascularity in animals that received alpha(nu)beta(3)-targeted paramagnetic nanoparticles increased 173% by 120 min. Signal contrast with nontargeted paramagnetic nanoparticles was approximately 50% less than that in the targeted group (P < 0.05). Molecular MRI results were corroborated by histology. In a competitive cell adhesion assay, incubation of alpha(nu)beta(3)-expressing cells with targeted nanoparticles significantly inhibited binding to a vitronectin-coated surface, confirming the bioactivity of the targeted nanoparticles. The present study lowers the limit previously reported for detecting sparse biomarkers with molecular MRI in vivo. This technique may be employed to noninvasively detect very small regions of angiogenesis associated with nascent melanoma tumors, and to phenotype and stage early melanoma in a clinical setting.

Novel rapid fat suppression strategy with spectrally selective pulses

Short repetition time gradient echo sequences are gaining popularity in clinical applications such as dynamic contrast enhancement imaging, cardiac imaging, and MR angiography. Performing fat suppression in these sequences is usually time consuming and often somewhat ineffective, due to the relatively short T(1) and long T(2) of fat. A novel rapid fat suppression strategy using spectrally selective pulses is introduced and compared with clinically popular sequences such as fat presaturated fast field echo (FFE) and turbo field echo (TFE) and binomial water-selective spatial-spectral excitation (SSE, or SPSP excitation) FFE. The new strategy combines fat presaturation with low-order binomial water-selective SSE pulses in a TFE sequence. This enables the use of a long echo train length to decrease exam time, but without creation of excess fat signal contamination of the resultant images. The fat nullification is also more reliable as fat signals in central k-space data are suppressed twice. An implementation of this strategy is compared with traditional methods in both phantom and human studies, confirming that the new technique provides strong fat suppression with few artifacts despite the short scan duration.

Three-dimensional fast field echo MR myelography using water excitation

The purpose of this study is to determine if 3D FFE MRM using WE provides better image quality in comparison with that using SPIR. Twenty subjects were referred for the MRM images using SPIR, and WE with different TR. SNR and CNR were measured in the ganglions and adjacent tissues, in addition, the uniformity of the fat tissues was scored on a three-point scale by two radiologists with consensus. The WE sequence showed the higher SNR and CNR values than that using SPIR, in addition, the WE technique was helpful to achieve the shorter acquisition time of MRM.

Optimization of Gd-DTPA-enhanced Balanced Turbo Field Echo Sequence in Abdominal Imaging: A Basic Study

PURPOSE

To determine the optimum imaging conditions for the balanced turbo field echo (bTFE) sequence in abdominal imaging, we performed phantom experiments and scanning of a normal volunteer while noting the correlation among signal intensity, k-space ordering, flow velocity and Gd-DTPA concentration.

MATERIALS AND METHODS

Initially, the abdomen of a healthy volunteer and some samples (water, blood and bovine albumin solutions with various Gd-DTPA concentrations, and olive oil) were examined with the bTFE sequence under various conditions to define the correlation among signal intensity, k-space ordering and Gd-DTPA concentration. Another experiment was performed to assess the correlation between the flow velocity and Gd-DTPA concentration. With the centric-bTFE sequence, we measured the signal intensity of water samples having various Gd-DTPA concentrations flowing in a long tube with an internal diameter of 4 mm.

RESULTS

The experiments revealed the following issues: (i) The contrast of bTFE images was much influenced by k-space ordering; (ii) Gd-DTPA did not exhibit an overt enhancement effect in water and blood under stable conditions; (iii) The signal intensity of moving water decreased in centric-bTFE images, and this signal drop became more significant as the fluid speed increased; and (iv) Gd-DTPA decreased the range of signal loss in the moving fluid; however, this effect had no correlation with Gd-DTPA concentration.

CONCLUSION

When the bTFE sequence was employed for abdominal imaging, centric view ordering, fat suppression and Gd-DTPA contrast enhancement were assumed to be necessary.

Estudo comparativo das seqüências rápidas ponderadas em T2, utilizando-se sincronização respiratória, apnéia, supressão de gordura, bobina de corpo e bobina de sinergia para a avaliação do fígado pela ressonância magnética

OBJETIVO: Comparar, qualitativa e quantitativamente, as imagens de ressonância magnética do fígado, ponderadas em T2, utilizando-se seqüências rápidas, diferenciadas pela técnica de controle respiratório, pela utilização de supressão de gordura e pelo tipo de bobina de radiofreqüência. MATERIAIS E MÉTODOS: Estudo prospectivo em 71 pacientes consecutivos, sendo realizadas seis seqüências para comparação: 1) supressão de gordura com sincronização respiratória e bobina de corpo; 2) supressão de gordura em apnéia e bobina de corpo; 3) sem supressão de gordura com sincronização respiratória e bobina de corpo; 4) sem supressão de gordura em apnéia e bobina de corpo; 5) com supressão de gordura com sincronização respiratória e bobina de sinergia; 6) com supressão de gordura em apnéia e bobina de sinergia. A avaliação qualitativa foi baseada em três critérios: detecção de determinadas estruturas anatômicas do fígado, definição dos contornos hepáticos, e presença de artefatos de respiração. A análise quantitativa foi obtida através da relação das intensidades de sinal do fígado e do ruído de fundo. RESULTADOS: O valor médio dos índices globais de qualidade de imagem para cada uma das seis seqüências supracitadas foi de 7,8, 4,6, 7,9, 5,2, 6,7 e 4,6, respectivamente. As seqüências obtidas com sincronização respiratória apresentaram melhor qualidade de imagem e relação sinal/ruído superiores às seqüências com apnéia (p < 0,001). As seqüências realizadas com e sem supressão de gordura apresentaram qualidade de imagem e relação sinal/ruído semelhantes (p > 0,05). As seqüências obtidas com bobina de sinergia apresentaram qualidade de imagem semelhante (p > 0,05) e relação sinal/ruído inferior àquelas com bobina de corpo (p < 0,001). CONCLUSÃO: Associando-se as análises qualitativa e quantitativa das imagens, as melhores seqüências foram aquelas obtidas com sincronização respiratória e bobina de corpo, utilizando-se ou não supressão de gordura.

Fat suppression strategies in enhanced MR imaging of the breast: comparison of SPIR and water excitation sequences

PURPOSE

To compare two fat suppression techniques of spectrally-selective inversion pulse (spectral presaturation with inversion recovery-SPIR) and spectral-spatial excitation pulse of water excitation (WE) for contrast-enhanced MR imaging of the breast.

MATERIALS AND METHODS

Forty women with histologically-proven breast cancer were examined. Both pulse types were applied to postcontrast, axial, three-dimensional field echo sequence. Contrast noise ratios (CNR) of lesion-to-breast parenchyma, lesion-to-fat, and parenchyma-to-fat were determined. Qualitative image analysis using a four-point scale was also performed by two observers.

RESULTS

All the CNR values of obtained with WE techniques were significantly higher than those with SPIR. Qualitative analysis indicated that the WE images were statistically superior for the lesion-to-breast parenchyma contrast while being slightly inferior to the SPIR images for fat suppression homogeneity without statistical significance.

CONCLUSION

Compared to SPIR, the WE technique suppressed the subcutaneous fat signal more potently and improved the contrast of the enhanced breast lesion against the parenchyma and the subcutaneous fat. WE will be a powerful fat suppression strategy for enhanced MR imaging of the breast.

Density of organic matrix of native mineralized bone measured by water- and fat-suppressed proton projection MRI

Water- and fat-suppressed projection MR imaging (WASPI) utilizes the large difference between the proton T(2) (*)s of the solid organic matrix and the fluid constituents of bone to suppress the fluid signals while preserving solid matrix signals. The solid constituents include collagen and some molecularly immobile water and exhibit very short T(2) (*). The fluid constituents include mobile water and fat, with long T(2) (*). In WASPI, chemical shift selective low-power pi/2 pulses excite mobile water and fat magnetization which is subsequently dephased by gradient pulses, while the magnetization of collagen and immobile water remains mostly in the z-direction. Additional selective pi pulses in alternate scans further cancel the residual water and fat magnetization. Following water and fat suppression, the matrix signal is excited by a short hard pulse and the free induction decay acquired in the presence of a gradient in a 3D projection method. WASPI was implemented on a 4.7 T MR imaging system and tested on phantoms and bone specimens, enabling excellent visualization of bone matrix. The bone matrix signal per unit volume of bovine trabecular specimens was measured by this MR technique and compared with that determined by chemical analysis. This method could be used in combination with bone mineral density measurement by solid state (31)P projection MRI to determine the degree of bone mineralization.

Feasibility of ultrasound examination in posterior ligament complex injury of thoracolumbar spine fracture

STUDY DESIGN

A prospective study of 12 patients with thoracolumbar spinal fractures was conducted.

OBJECTIVE

To assess the feasibility of ultrasound examination for posterior ligament complex injury in thoracolumbar spinal fractures.

SUMMARY OF BACKGROUND DATA

In posterior ligament complex injury of thoracolumbar spine fracture, the reliability of magnetic resonance imaging (MRI) for diagnosis has been reported. Nevertheless the usefulness of ultrasound for diagnosis has not been studied, whereas diagnostic ultrasound has been applied in the musculoskeletal system.

METHODS

Two healthy volunteers without a history of spinal trauma were recruited for pilot examination of the ultrasound procedure to access normal findings of the posterior ligament complex. This study investigated 12 thoracolumbar spine fractures. Four were flexion distraction injury; six were stable or unstable burst fractures; and two were simple compression fractures. Osteoporotic spine fractures were excluded from this study. Ultrasound was performed over the injured area by an experienced musculoskeletal radiologist in addition to radiography and MRI. Five patients underwent operative procedures to stabilize the fractured spine. Imaging data and operative findings were correlated with ultrasound examination.

RESULTS

In the patients who did not undergo surgery, agreement in diagnosis between MRI and ultrasound was moderate (5 of 7). Difficulty evaluating ligament status was encountered when the region of interest was the lower thoracic level (T10, T11, T12) because of long overlapping spinous processes. In the patients who underwent surgery, correlation between MRI, ultrasound, and operative findings was excellent, especially in diagnosing the status of the supraspinous and interspinous ligaments. Nevertheless, it is impossible to visualize deep-seated structures (i.e., ligamentum flavum, deep muscles of the spine, and facet joint) with ultrasound.

CONCLUSIONS

This study demonstrated the excellent diagnostic ability of ultrasound to detect the status of the supraspinous and interspinous ligaments, especially in patients who undergo surgery. Although ultrasound examination appears to be less sensitive than MRI in predicting ligament status, the cost effectiveness of ultrasound and its use as an alternative to MRI in special situations (i.e., patients with pacemaker, ferromagnetic implant, or severe claustrophobia) should be emphasized. More clinical data concerning the sensitivity, specificity, and accuracy of ultrasound examination should be addressed in future studies.

Reliability of magnetic resonance imaging in detecting posterior ligament complex injury in thoracolumbar spinal fractures

STUDY DESIGN

Prospective study of 34 patients with thoracolumbar spinal fractures.

OBJECTIVES

To assess the reliability of magnetic resonance imaging (MRI) for posterior ligament complex injury in thoracolumbar spinal fractures.

SUMMARY OF BACKGROUND DATA

Some researchers have studied posterior ligament complex injury in spinal fracture using MRI. However, most did not evaluate the findings of MRI compared with the operative findings.

METHODS

Thirty-four patients with thoracolumbar spinal fracture were evaluated by palpation of the interspinous gap, plain radiography, and MRI before operation. In addition to conventional MRI sequences, a fat-suppressed T2-weighted sagittal sequence was performed. Surgery was performed by a posterior approach. During the operation, posterior ligament complex injury was carefully examined.

RESULTS

A wide interspinous gap was palpated in 14 patients and was found in 21 patients on plain radiography. Magnetic resonance imaging raised suspicion of injury to the posterior ligament complex in 30 patients. According to interpretation of MRI, injury to the supraspinous ligament was suspected in 27 patients, the interspinous ligament in 30 patients, and the ligamentum flavum in 9 patients. There were 28 supraspinous ligament injuries, 29 interspinous ligament injuries, and 7 ligamentum flavum injuries in operative findings. There was a significant relation between MRI interpretation and operative findings.

CONCLUSION

A fat-suppressed T2-weighted sagittal sequence of MRI was a highly sensitive, specific, and accurate method of evaluating posterior ligament complex injury. Based on the results of this study, a fat-suppressed T2-weighted sagittal sequence of MRIs is recommended for the accurate evaluation of posterior ligament complex injury and would be helpful in the selection of treatment options.

Magnetic resonance imaging in rheumatic disorders of the spine and sacroiliac joints

OBJECTIVE

To review the value of magnetic resonance imaging (MRI) in diagnosis and evaluation of rheumatic diseases of the spine and sacroiliac joints.

METHODS

A review of the literature on MRI of the spine and sacroiliac joints in rheumatoid arthritis (RA), ankylosing spondylitis (AS), infectious spondylodiscitis, infection of the sacroiliac joint (SIJ), gout, calcium pyrophosphate deposition disease, nontraumatic vertebral compression fractures, insufficiency fracture of the sacrum, avascular necrosis of the vertebral body, sarcoidosis, and Paget's disease was performed. The reports were obtained from a Medline search.

RESULTS

In RA, AS, and crystal deposition disease, synovial tissue, atlantoaxial and subaxial subluxations, crystal deposition, and neurologic compromise can be adequately diagnosed with MRI of the cervical spine. Studies on MRI of SIJs in AS indicate that MRI enables early diagnosis of sacroiliitis. In most cases of infectious spondylodiscitis, avascular necrosis of the vertebral body, nontraumatic vertebral compression fractures, and insufficiency fractures of the sacrum characteristic findings on MRI suggest the correct diagnosis. Moreover, soft tissue abnormalities and neurologic compromise can be visualized. In infection of the SIJ, MRI shows findings suggesting an inflammatory process. In Paget's disease, MRI does not provide additional information as compared with plain radiography (PR) or computed tomography (CT).

CONCLUSION

In evaluation of spinal and SIJ abnormalities in many rheumatic diseases, MRI, in addition to PR, can replace conventional tomography, CT, and myelography. Moreover, MRI can visualize soft tissue abnormalities and neurologic compromise without use of intrathecal contrast.

Mature cystic teratomas of the ovary: CT and MR findings

OBJECTIVE

To correlate CT and MR patterns of ovarian mature cystic teratomas (MCT).

SUBJECTS AND METHODS

CT and MR findings in 25 histologically proven ovarian MCT were retrospectively reviewed. MCT characterization at CT and MR was based on detection of fat and/or a Rokitansky protuberance. MR signal intensity and CT density numbers of fat were correlated.

RESULTS

At pathology, 24/25 tumors contained fat, 1/25 a water content, and 23/25 a Rokitansky protuberance. Twenty one MCT contained fat with a density number less than-20 HU (mean density: -95 HU) and a signal intensity superior or equal to sub-cutaneous fat on T1 images, however, only six of these had a signal intensity equal to sub-cutaneous fat on T1 and T2 images and 12 had a reversed chemical shift artifact. Three contained fat with a density number ranging from -13 to +8 HU and a signal intensity inferior to subcutaneous fat on T1 images. CT showed a Rokitansky protuberance in 21/23, containing adipose tissue in 16 and calcified structures in 21. Standard MR showed a Rokitansky protuberance in 14/23 and characterized adipose tissue in eight cases, and calcified material in six cases. Finally, CT characterized 24/25 (96%) MCT. Standard MR characterized 22/25 (88%) MCT, and standard MR with fat-suppression sequences characterized 23/25 (92%) MCT.

CONCLUSION

Standard MR is less effective than CT in characterizing fat and has the same difficulty as CT in characterizing fat mixed with hair when its density is high. When fat cannot be identified by either technique, diagnosis of a Rokitansky protuberance is more easily made at CT than at MR.

Fat suppression techniques in MR imaging of mature ovarian teratomas: comparison with CT

OBJECTIVE

The aim of this study is to analyze the ability of MR fat suppression techniques to characterize fat components of ovarian mature cystic teratomas (MCT) shown by CT.

SUBJECTS AND METHODS

MR images of eight MCTs of the ovary were obtained using standard sequences followed by a SPIR (spectral presaturation with inversion recovery) sequence in six cases and by Dixon sequences in two cases. In all cases correlation with CT and pathologic findings was achieved.

RESULTS

MR fat suppression sequences showed to be as accurate as CT in detecting fat inside the cystic part of the teratomas (8/8).

CONCLUSION

MR fat suppression sequences should be performed when presence of fat is suspected on images of ovarian tumors produced by standard MR sequences.