The value of specific MRI features in the evaluation of suspected placental invasion

OBJECTIVE: The objective of this study was to determine imaging features that may help predict the presence of placenta accreta, placenta increta or placenta percreta on prenatal MRI scanning. SUBJECTS AND METHODS: A retrospective review of the prenatal MR scans of 10 patients with a diagnosis of placenta accreta, placenta increta or placenta percreta made by pathologic and clinical reports and of 10 patients without placental invasion was performed. Two expert MRI readers were blinded to the patients' true diagnosis and were asked to score a total of 17 MRI features of the placenta and adjacent structures. The interrater reliability was assessed using kappa statistics. The features with a moderate kappa statistic or better (kappa > .40) were then compared with the true diagnosis for each observer. RESULTS: Seven of the scored features had an interobserver reliability of kappa > .40: placenta previa (kappa = .83); abnormal uterine bulging (kappa = .48); intraplacental hemorrhage (kappa = .51); heterogeneity of signal intensity on T2-weighted (T2W) imaging (kappa = .61); the presence of dark intraplacental bands on T2W imaging (kappa = .53); increased placental thickness (kappa = .69); and visualization of the myometrium beneath the placenta on T2W imaging (kappa = .44). Using Fisher's two-sided exact test, there was a statistically significant difference between the proportion of patients with placental invasion and those without placental invasion for three of the features: abnormal uterine bulging (Rater 1, P = .005; Rater 2, P = .011); heterogeneity of T2W imaging signal intensity (Rater 1, P = .006; Rater 2, P = .010); and presence of dark intraplacental bands on T2W imaging (Rater 1, P = .003; Rater 2, P = .033). CONCLUSIONS: MRI can be a useful adjunct to ultrasound in diagnosing placenta accreta prenatally. Three features that are seen on MRI in patients with placental invasion appear to be useful for diagnosis: uterine bulging; heterogeneous signal intensity within the placenta; and the presence of dark intraplacental bands on T2W imaging.     

Diagnostic value of breast MRI for predicting metastatic axillary lymph nodes in breast cancer patients: diffusion-weighted MRI and conventional MRI

Purposes

To evaluate the diagnostic value of diffusion-weighted MRI (DWI) and combination of conventional MRI and DWI to predict metastatic axillary lymph nodes in breast cancer.

Materials and methods

Two hundred fifty-two breast cancer patients with 253 axillae were included. The morphological parameters on axial T2-weighted images without fat saturation and apparent diffusion coefficient (ADC) values were retrospectively analyzed. An independent t-test/chi-square test and receiver operating characteristics (ROC) curve analysis were used.

Results

On conventional MRI, short and long axis length, maximal cortical thickness, relative T2 value, loss of fatty hilum (p < 0.001 for each), and eccentric cortical thickening (p < 0.003) were statistically significantly different between the metastatic and nonmetastatic groups. The short axis to long axis ratio was not a statistically significant parameter. The ADC value was significantly different between the 2 groups, with an AUC that was higher than that of conventional MR parameters (AUC, 0.815; threshold, ≤ 0.986 × 10–3 mm²/sec; sensitivity, 75.8%; specificity, 83.9%). Using the adopted thresholds for each parameter, a total number of findings suggesting malignancy of 4 or higher was determined as the threshold, with high specificity (90.1%).

Conclusion

Using conventional MRI and DWI, we can evaluate the axilla in breast cancer with high specificity.     

The value of diffusion-weighted MRI to evaluate the response to radiochemotherapy for cervical cancer

Purpose

To investigate the value of apparent diffusion coefficient (ADC) to predict and monitor the therapy response for cervical cancer patients receiving concurrent radiochemotherapy, and to analyze the influence of different b-value combinations on ADC-based evaluation of treatment response.

Material and Methods

Seventy-five cervical cancer patients treated with radiochemotherapy received conventional MRI and DWI prior to therapy, after 2 weeks of therapy, after four weeks of therapy and after therapy completion. Treatment response was classified as complete response (CR, n = 35), partial response (PR, n = 22) and stable disease (SD, n = 18), which was determined according to final tumor size after 6 months of therapy completion. Dynamic changes of apparent diffusion coefficients (ADC) and tumor size in the three tumor groups were observed and compared. All the ADCs were calculated from b = 0, 600 s/mm² and b = 0, 1000 s/mm².

Results

The ADC increased percentage was higher in CR group than those in PR and SD groups after two weeks and four weeks of therapy, with significant differences in absolute ADCs between CR and PR, SD groups after therapy completion; the overall discriminatory capability for differentiation of CR and PR, SD groups was higher for high b-value combination (0, 1000 s/mm²) than for low b-value combination (0, 600 s/mm²).

Conclusion

DWI can be used as a predictive and monitoring biomarker of treatment response to radiochemotherapy in patients with cervical cancer. High b-value combination may be more reliable to evaluate the treatment response for cervical cancer.     

Cardiac MRI cine and color Doppler in valvular disease: correlative imaging

Cardiac cine field echo MRI and color Doppler were performed in 13 patients with aortic regurgitation (n = 4) or multiple valvular diseases (n = 9). The size, shape, and direction of regurgitation jets correlated well. Color Doppler was better able to follow flow jets in oblique planes. Cine MRI was better able to evaluate patients with marked cardiac dilatation.     

MRI evaluation of brain iron in earlier- and later-onset Parkinson's disease and normal subjects

Tissue iron levels in the extrapyramidal system of earlier- and later-onset Parkinson's disease (PD) subjects were evaluated in vivo using a magnetic resonance imaging (MRI) method. The method involves scanning subjects in both high- and low-field MRI instruments, measuring tissue relaxation rate (R2), and calculating the field-dependent R2 increase (FDRI) which is the difference between the R2 measured with the two MRI instruments. In tissue, only ferritin iron is known to increase R2 in a field-dependent manner and the FDRI measure is a specific measure of this tissue iron pool. Two groups of male subjects with PD and two age-matched groups of normal control males were studied. The two groups of six subjects with PD consisted of subjects with earlier- or later-onset (before or after age 60) PD. FDRI was measured in five subcortical structures: the substantia nigra reticulata (SNR), substantia nigra compacta (SNC), globus pallidus, putamen, and caudate nucleus, and in one comparison region; the frontal white matter. Earlier-onset PD subjects had significant (p < 0.05) increases in FDRI in the SNR, SNC, putamen, and globus pallidus, while later-onset PD subjects had significantly decreased FDRI in the SNR when compared to their respective age-matched controls. Controlling for illness duration or structure size did not meaningfully alter the results. Published post-mortem studies on SN iron levels indicate decreased ferritin levels and increased free iron levels in the SN of older PD subjects, consistent with the decreased FDRI observed in our later-onset PD sample, which was closely matched in age to the post-mortem PD samples. The FDRI results suggest that disregulation of iron metabolism occurs in PD and that this disregulation may differ in earlier- versus later-onset PD.     

Differentiation of bone metastases from prostate cancer and benign red marrow depositions of the pelvic bone with multiparametric MRI

PurposeTo investigate the diagnostic utilities of imaging parameters derived from T1-weighted imaging (T1WI), diffusion-weighted imaging (DWI) and dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) to differentiate bone metastases from prostate cancer and benign red marrow depositions of the pelvic bone.Materials and methodsThirty-six lesions from 36 patients with prostate cancer were analyzed with T1WI, DWI, and DCE-MRI. The lesions were classified in the bone metastases (n = 22) and benign red marrow depositions (n = 14). Lesion-muscle ratio (LMR), apparent diffusion coefficient (ADC), volume transfer constant (K^trans), reflux rate (Kep), and volume fraction of the extravascular extracellular matrix (Ve) values were obtained from the lesions. The imaging parameters of the both groups were compared using the Mann-Whitney U test, receiver operating characteristics (ROC) curves were analyzed. For the ROC curves, area under the curves (AUCs) were compared.ResultsThe ADC, K^trans, K_ep, and V_e values of bone metastases were significantly higher than those of benign red marrow depositions (Mann-Whitney U test, p < 0.05). However, there was no significant difference in LMR between the two groups (Mann-Whitney U test, p = 0.360). The AUCs of K^trans_, K_ep, ADC, V_e, and LMR were 0.896, 0.844, 0.812, 0.724, and 0.448, respectively. In the pairwise comparison of ROC curves, the AUCs of K^trans and K_ep was significantly higher than LMR.ConclusionsK^trans, K_ep, V_e, and ADC values can be used as imaging tools to differentiate bone metastases from prostate cancer and benign red marrow depositions of the pelvic bone.     

MRI characterization of residual mediastinal masses in Hodgkin's disease: long-term follow-up

Our purpose was to evaluate the role of MRI in distinguishing fibrous from active residual masses in treated Hodgkin's disease. Forty patients with residual mediastinal mass larger than 1.5 cm underwent MRI 1, 3, 6, and 12 months after the end of cycles of prescribed chemotherapy or combined chemoradiotherapy. The MRI examinations were performed on a 0.5 and a 1.5 T systems, using T(1) before and after gadolinium injection and T(2)-weighted sequences. Each time the residual mass was evaluated in size and signal intensity on spin echo (SE) T(2)-weighted images and on SE T(1)-weighted images after contrast medium. Low signal intensity and low contrast enhancement were considered signs of inactive residues; homogeneous high signal intensity and high contrast enhancement were indicative of active residual disease; heterogeneous signal intensity and heterogeneous contrast enhancement were indicative of partial remission or necrotic/inflammatory phenomena. MR showed high diagnostic accuracy in the evaluation of Hodgkin's mediastinal residues after treatment, if performed at least 6 months after the end of therapy, reaching the highest sensitivity and specificity values at 12 month follow-up (considering the three parameters-T(2) signal intensity, contrast-enhancement, and size-all together). If we consider the single parameters individually, we can observe that size variation remains the more valuable parameter to predict or to exclude a relapse. MR diagnostic accuracy at the 6-month follow-up was lower due to the higher incidence of inhomogeneous pattern. The accuracy of MR performed at 1 and at 3 months after the end of therapy was not satisfying. This represents a clinical problem because the most important clinical decisions have to be taken just in this early post-treatment phase.     

A preliminary study of blood-oxygen-level-dependent MRI in patients with chronic kidney disease

Background

Blood-oxygen-level-dependent (BOLD) magnetic resonance imaging (MRI) can provide regional measurements of oxygen content using deoxyhemoglobin paramagnetic characteristics. The apparent relaxation rate or R2*(=1/T2*) can be determined from the slope of log (intensity) versus echo time and is directly proportional to the tissue content of deoxyhemoglobin. Thus, as the level of deoxyhemoglobin increases, T2* will decrease, leading to an increase in R2*. Chronic kidney disease (CKD) can affect oxygenation levels in renal parenchyma, which influences the clinical course of the disease. The goal of this study was to detect and assess renal oxygenation levels in CKD using BOLD MRI.

Methods

Fifteen healthy subjects and 11 patients with CKD underwent a renal scan using multigradient-recalled-echo sequence with eight echoes. R2* (1/s) of the renal cortex and medulla was measured on BOLD images. Of the 11 patients, nine had biopsy-proven chronic glomerulonephritis, and two had a similar diagnosis based on clinical symptoms and investigations.

Results

Mean medullary R2* (MR2*) and cortex R2* (CR2*) levels were significantly higher in patients (22 kidneys, MR2*=24.79±4.84 s⁻¹, CR2*=18.97±2.72 s⁻¹) than in controls (30 kidneys, MR2*=19.98±1.19 s⁻¹, CR2*=16.03±1.23 s⁻¹) (P<.01), and MR2* was increased more than CR2*. Medullary to cortical R2* ratios (MCR2*) of patients were significantly increased when compared with those of controls (P<.01). In the patient group, estimated glomerular filtration rate levels were greater than or equal to 60 ml/min/1.73 m² in six patients (12 kidneys), whose MR2* and CR2* were also significantly higher than those of controls (P<.01). Serum creatinine levels were normal in seven patients (14 kidneys), whose MR2*, CR2* and MCR2* were also higher than those of controls (P<.01).

Conclusions

BOLD MRI can be used to evaluate changes in renal oxygenation in CKD, suggesting that it has the potential to be an excellent noninvasive tool for the evaluation of renal function.     

Acute effects of exercise on muscle MRI in peripheral arterial occlusive disease

The midcalf muscles of eight patients who had peripheral arterial occlusive disease were evaluated by exercise MRI before and after bypass surgery or percutaneous transluminal angioplasty. MRI showed a high intensity of these muscles, especially the posterior muscles, after exercise in all patients before intervention. The mean T₂ relaxation time was maximal immediately after exercise (tibialis anterior, T₂ = 30.8 ms; soleus, T₂ = 36.2 ms; gastrocnemius, T₂ = 32.8 ms) and then gradually decreased to the preexercise level. The difference in the T₂ relaxation time of the soleus between immediately after exercise and at rest was smaller along with improvement of ankle pressure indices (API) after successful intervention (mean T₂ difference: 4.91 and 0.72 ms (p < .001); mean API: 0.54 and 0.86 (p < .001) before and after intervention, respectively). The mean resting midcalf T₂ relaxation time was significantly higher after intervention (tibialis anterior, T₂ = 28.4 and 29.5 ms (p < .05); soleus, T₂ = 31.4 and 32.9 ms (p < .05); gastrocnemius, T₂ = 29.5 and 31.1 ms (p < .01) before and after intervention, respectively). T₂ relaxation time may be a useful quantitative parameter in peripheral arterial occlusive disease as well as in other muscle studies.     

Values of intravoxel incoherent motion diffusion weighted imaging and dynamic contrast-enhanced MRI in evaluating the activity of sacroiliitis in ankylosing spondylitis of rat model

ObjectiveTo prospectively evaluate the ability of IVIM-DWI and DCE-MRI in detecting early activity of sacroiliitis in rat model of ankylosing spondylitis by comparing with pathological results.Methods20 wistar male rats were induced by bovine proteoglycan combined with complete/incomplete Freund's adjuvant as model group, and 20 healthy male rats were used as the control group. The parameters of IVIM-DWI and DCE-MRI in synovial regions of SIJ were measured respectively at 7th, 12th, 17th, and 22th weeks after the last induction, and the pathological features of SIJ were taken also, further studying the pathological characteristics of sacroiliac region. Independent sample t-test and one-way ANOVA were used for statistical analysis. The prediction parameters and diagnostic efficiency were compared by ROC curve.ResultsThere was no significant difference of image parameters between the model and control groups at the 7th, 12th weeks after the last induction, and there were no positive findings in histopathological examination at the same time. At the 17th week after induction, the f and Fenh%, Senh% between the model and the control groups were statistically significant. At the 22th week, there was a statistically significant increase all the values in model group than those in control group (P < 0.05). Histologic examination confirmed inflmmtorycell infiitrtion at the 17th week and pannus forming of synovium on the surface of cartilage at the 22th week in the model groups. The Fenh%, Senh%, D_slow and f had the moderate diagnostic efficiency and the areas under the curve were 0.77, 0.75, 0.77 and 0.82 respectively. The Senh% demonstrated the highest sensitivity (71.4%) and f demonstrated the highest specificity (95.0%).ConclusionIVIM-DWI and DCE-MRI can be used as the sensitive imaging methods to detect and accurate diagnosis the early activity of sacroiliitis in AS.     

The amount and value of information in biology

The notion of the value of information is discussed. The value one attributes to information is determined by the result of its reception by an open nonequilibrium system. Qualitative reasoning shows that the concept of value of information makes sense only in nonequilibrium situations, and is directly connected with the nonredundancy of information. In biology it is the value and not the amount of information that is important. The value of information is especially high if there are instabilities in the system; these are connected with the notions of purpose and of freedom of will. The notion of selective value, introduced by Eigen in the theory of the prebiological evolution of macromolecules, is discussed. The amount of information in various codons is calculated and the conventional definition of its value is given based on the determination of the danger of the replacement of one amino acid by another with a different value of hydrophobicity. It is shown that the relative probability of transversion is considerably lower than that of transition. As most nonsense mutations are transversions, the genetic code provides decreased probability for the most dangerous mutations. It is shown that the information of the codonUGG(Trp) is highest in both amount and value.     

Alzheimer''s disease histologically proven studied by MRI and MRS: Two cases

Two patients affected by severe Alzheimer's disease (AD) were investigated by MRI and image-guided ³¹P MRS. In one case, ¹H MRS was additionally performed. In both cases the diagnosis of AD was confirmed, post mortem, by the pathologist. The spectral parameters of the ³¹P MR spectra were estimated by fitting the ³¹P MR signals in the time domain. Our ³¹P MRS results suggest that it is possible to detect the membrane catabolism, as indexed with the level of PDE resonances visible in in vivo ³¹P MRS, at least in severe AD cases. The ¹H spectrum from AD brain showed a marked decrease of NAA signal respect to choline.     

The suppression of selected acoustic frequencies in MRI

A study is made of certain dominant frequencies in the acoustic noise spectrum of the magnetic resonance imaging system. Motivated by both spring and string ideas, we investigate whether the contributions to the sound from certain frequencies can be canceled by the appropriate gradient pulse sequence design. From both simulations and experiments, vibrations resulting from an impulsive force associated with a ramping up of a gradient pulse are shown to be cancelled immediately upon the application of another impulsive force coming from the subsequent appropriately timed ramping down of that pulse. A general approach to suppression of multiple-frequency contributions involving a series of gradient pulses with variable timings is given for the cancellations between pairs of impulsive forces. Various examples are confirmed through string simulations, MRI experiments, and linear response theory. This also provides a foundation to explain some results in previous papers on this subject. The method suggests that a variety of pulse profiles and timing combinations can be used to attenuate important contributions to the acoustic spectrum.     

Non-Gaussian diffusion MRI assessment of brain microstructure in mild cognitive impairment and Alzheimer’s disease

We report the first application of a novel diffusion-based MRI method, called diffusional kurtosis imaging (DKI), to investigate changes in brain tissue microstructure in patients with mild cognitive impairment (MCI) and AD and in cognitively intact controls. The subject groups were characterized and compared in terms of DKI-derived metrics for selected brain regions using analysis of covariance with a Tukey multiple comparison correction. Receiver operating characteristic (ROC) and binary logistic regression analyses were used to assess the utility of regional diffusion measures, alone and in combination, to discriminate each pair of subject groups. ROC analyses identified mean and radial kurtoses in the anterior corona radiata as the best individual discriminators of MCI from controls, with the measures having an area under the ROC curve (AUC) of 0.80 and 0.82, respectively. The next best discriminators of MCI from controls were diffusivity and kurtosis (both mean and radial) in the prefrontal white matter (WM), with each measure having an AUC between 0.77 and 0.79. Finally, the axial diffusivity in the hippocampus was the best overall discriminator of MCI from AD, having an AUC of 0.90. These preliminary results suggest that non-Gaussian diffusion MRI may be beneficial in the assessment of microstructural tissue damage at the early stage of MCI and may be useful in developing biomarkers for the clinical staging of AD.     

q-Space high b value diffusion MRI of hemi-crush in rat spinal cord: evidence for spontaneous regeneration

The development of the damage following hemi-crush trauma in rat spinal cord was studied ex vivo using high b value (bmax = 1 x 10(7) s cm(-2)) q-space diffusion weighted MRI (DWI) at five days, ten days and six weeks post-trauma. Rat spinal cord trauma, produced by hemi-crush of 15s and 60s duration, was studied. The water signal decay in these diffusion experiments was found to be non mono-exponential and was analyzed using the q-space approach. The q-space MRI parameters were compared with T1 and T2 MR images, behavioral tests and histopathological osmium staining. A very good anatomical correlation was found between the q-space MRI parameters and the osmium staining. Interestingly, we found that in the 15s hemi-crush model significant recovery was observed in both the q-space MR images and the osmium staining six weeks post-trauma. However, in the 60s hemi-crush trauma model very little recovery was observed. These results paralleled those obtained from behavioral tests demonstrating that partial spontaneous recovery seems to occur in the 15s hemi-crush spinal cord model, which should be taken in consideration when using it to evaluate new therapies.     

The value of singularities

We point out that spacetime singularities play a useful role in gravitational theories by eliminating unphysical solutions. In particular, we argue that any modification of general relativity which is completely nonsingular cannot have a stable ground state. This argument applies both to classical extensions of general relativity, and to candidate quantum theories of gravity.This essay received the first award from the Gravity Research Foundation, 1995-Ed.