Transudative vs exudative pleural effusions: differentiation using Gd-DTPA-enhanced MRI

The aim of this study was to investigate the capability of Gd-DTPA-enhanced MRI to differentiate between exudative and transudative pleural effusions. An MRI examination was performed on 22 patients with different types of pleural effusion (10 transudative and 12 exudative effusions). T1-weighted SE images were obtained before and 20 min after administration of Gd-DTPA (0.1 mmol/kg). The degree of enhancement of pleural effusions was evaluated both by visual assessement and by quantitative analysis of images. None of 10 transudative effusions showed significative enhancement, whereas 10 of 12 exudative effusions showed enhancement (sensitivity 83 %, specificity 100 %, positive predictive value 100 %). The postcontrast signal intensity ratios (SIRs) of exudates were significantly higher than corresponding precontrast ratios (P = 0.0109) and the postcontrast SIRs of exudates were significantly higher than those of transudates (P = 0.0300). Exudative pleural effusions show a significant enhancement following administration of Gd-DTPA. We presume that this may be caused by increased pleural permeability and more rapid passage of a large amount of Gd-DTPA from the blood into the pleural fluid in case of exudative effusions. In our limited group of patients, signal enhancement proved the presence of an exudative effusion. Absence of signal enhancement suggests a transudate, but does not exclude an exudate. Received 9 April 1996; Revision received 12 August 1996; Accepted 4 October 1996     

Real-time sonography of pleural opacities

Fifty patients with radiographic pleural or pleural-based opacities were examined with high resolution real-time sonographic sector scanning. In 90% of cases selected for thoracentesis, fluid sufficient for diagnosis was obtained. Complex, septated pleural loculations contained an exudative effusion in 74% of the patients, while anechoic areas yielded exudative and transudative effusions with almost equal frequency. The use of real-time scanning is stressed because of greater flexibility and shorter examination time compared to compound scanning, and its utility for portable scanning on critically ill patients.     

Reproducibility of brain ADC histograms

The aim of this study was to assess the effect of differences in acquisition technique on whole-brain apparent diffusion coefficient (ADC) histogram parameters, as well as to assess scan–rescan reproducibility. Diffusion-weighted imaging (DWI) was performed in 7 healthy subjects with b-values 0–800, 0–1000, and 0–1500 s/mm² and fluid-attenuated inversion recovery (FLAIR) DWI with b-values 0–1000 s/mm². All sequences were repeated with and without repositioning. The peak location, peak height, and mean ADC of the ADC histograms and mean ADC of a region of interest (ROI) in the white matter were compared using paired-sample t tests. Scan–rescan reproducibility was assessed using paired-sample t tests, and repeatability coefficients were reported. With increasing maximum b-values, ADC histograms shifted to lower values, with an increase in peak height (p<0.01). With FLAIR DWI, the ADC histogram shifted to lower values with a significantly higher, narrower peak (p<0.01), although the ROI mean ADC showed no significant differences. For scan–rescan reproducibility, no significant differences were observed. Different DWI pulse sequences give rise to different ADC histograms. With a given pulse sequence, however, ADC histogram analysis is a robust and reproducible technique. Using FLAIR DWI, the partial-voluming effect of cerebrospinal fluid, and thus its confounding effect on histogram analyses, can be reduced.     

Efficacy of CT in diagnosis of transudates and exudates in patients with pleural effusion

PURPOSE

We aimed to evaluate the efficacy of multidetector computed tomography (CT) imaging in diagnosis of pleural exudates and transudates using attenuation values.

MATERIALS AND METHODS

This retrospective study included 106 patients who were diagnosed with pleural effusion between January 2010 and June 2012. After the patients underwent chest CT, thoracentesis was performed in the first week. The attenuation values of the pleural effusions were measured in all patients.

RESULTS

According to Light’s criteria, 30 of 106 patients with pleural effusions had transudates, and the remaining patients had exudates. The Hounsfield unit (HU) value of the exudates (median, 12.5; range, 4–33) was significantly higher than that of the transudates (median, 5; range, 2–15) (P = 0.001). Additionally, when evaluated by disease subgroups, congestive heart failure and empyema were predictable in terms of median HU values of the pleural effusions with high and moderate sensitivity and specificity values (84.6% and 81.2%, respectively; 76.9% and 66.7%, respectively). Compared with other patients, the empyema patients had significantly more loculation and pleural thickening.

CONCLUSION

CT attenuation values may be useful in differentiating exu-dates from transudates. Although there is an overlap in most effusions, exudate can be considered when the CT attenuation values are >15 HU. Because of overlapping HU values, close correlation with clinical findings is essential. Additional signs, such as fluid loculation and pleural thickness, should be considered and may provide further information for the differentiation.Pleural effusion is a common clinical problem; indeed, it can arise from many diseases (1, 2). The first step in assessing a pleural effusion is to decide whether the pleural fluid is a transudate or an exudate (3). Transudate is caused by imbalances in hydrostatic and oncotic forces. It results from diseases such as heart failure, kidney failure, and cirrhosis. However, an exudate occurs when local factors influencing the accumulation of pleural fluid are altered. Exudates can be caused by clinical conditions such as pneumonia, malignancy, and thromboembolism (4).Although clinical and radiological findings may provide significant evidence about the cause(s) of pleural effusion(s), it may still be necessary to evaluate some cases with diagnostic thoracentesis (4, 5). Clinically, exudative effusion can be successfully separated from transudative effusion using Light’s criteria. The nature of the pleural effusion is based on diagnostic thoracentesis (1, 2). However, computed tomography (CT) can be used to evaluate the nature of pleural effusions to avoid the complications of thoracentesis (6, 7). Features such as pleural nodules, pleural thickening, loculation, extrapleural fat tissue thickness, and effusion density can be evaluated by CT to discriminate between exudates and transudates (8). Only two reported studies have examined CT attenuation values in patients with pleural effusions (9, 10); these showed different attenuation values for evaluation of pleural effusions.The aim of the present study was to evaluate the efficacy of multidetector CT (MDCT) images in diagnosing pleural exudates and transudates using attenuation values.     

The extrapleural fat in empyema: CT appearance

Pleural empyema can be accompanied by changes in the adjacent chest wall. We examined the chest wall on computed tomographic scans in 24 patients with pleural effusions. Eighteen patients had pleural empyema and six had transudative effusions. Of the 18 empyema patients, 13 had abnormally high attenuation in the extrapleural tissues. In 12 of these 13, the high attenuation was probably caused by reaction to the pleural infection. In two, it was probably caused by haematoma (one patient had haematoma and empyema). In five patients there was either no clear abnormality in the extrapleural space or an insufficient amount of fat to permit detection of an abnormality, or the parietal pleura could not be distinguished from the pleural fluid because intravenous contrast medium was not given. Of the six patients with proven transudative pleural effusions, all had extrapleural fat which appeared normal. Abnormally high attenuation in the extrapleural tissues can be expected to accompany exudative pleural effusion, particularly empyema, but not transudative effusion.     

Clinical single-shot diffusion-weighted MRI of the human brain on a short-bore medium-field imager

Diffusion-weighted MRI (DWI) is becoming important for assessment of acute stroke. Until recently single-shot DWI required expensive technology such as echo-planar imaging (EPI) available only at some research sites. A new medium-field (1.0 T) short-bore MR imager has been developed with which DWI data sets can be acquired. We prospectively studied 169 patients on this 1.0 T commercial system. After conventional imaging, DWI was performed with a single-shot multi-slice sequence with b values 0 an 900 s/mm², and with the gradients switched in three directions. The apparent diffusion coefficients were calculated with online calculation software. There were 50 patients with totally normal MRI, and 17 had strokes, these strokes were detected as areas of high signal on the images at a maximal b value. There was a drop in the ADC in ischaemic regions: in subacute infarcts, the values were between 0.41 and 0.531 × 10^{− 3} mm²/s. In old infarcts the ADC was 1.15 × 10^{− 3} mm²/s. Cerebrospinal fluid (CSF) gave low signal whereas areas in the brain had more intermediate intensities (CSF: 3.00; deep white matter: 0.75, cortical grey matter: 0.80, basal ganglia (thalamus): 0.70 and cerebellar white matter: 0.65 × 10^{− 3} mm²/s. Anisotropy was detected as areas of restricted diffusion along the tracts. These preliminary data show that DWI can be aquired successfully on a medium-field short-bore system. This should allow the technique to be implemented at more sites, therefore facilitating the diagnosis of acute stroke and rendering early intervention feasible. Received: 22 February 1999 Accepted: 27 April 1999     

Optimization of b value in diffusion-weighted MRI for the differential diagnosis of benign and malignant vertebral fractures

Objective The objective was to explore the optimal b value in diffusion-weighted imaging (DWI) of MRI for differential diagnosis of benign and malignant vertebral fractures. Materials and Methods Thirty-four consecutive patients with vertebral compression fractures underwent sagittal diffusion-weighted imaging (DWI) with different b values. The group included 14 patients with 18 benign vertebral fractures due to osteoporosis and/or trauma and 20 patients with 27 malignant vertebral fractures due to malignancy. The quality of the images was analyzed qualitatively on a three-point scale and quantitatively by measurement of the signal-to-noise ratio (SNR). Apparent diffusion coefficient (ADC) values were also calculated. Results Smaller b values correlated with better DW image quality. We found significant differences in the qualitative points values among the DW images with different b values (F = 302.18, p < 0.001). The mean SNR of the images ranged from 21.75 ± 3.64 at a b value of 0 s/mm² to 5.31 ± 3.17 at a b value of 800 s/mm². The SNR of DWI with a b value of 300 s/mm² (18.62 ± 2.47) was significantly different from that with other b values (p < 0.01). The mean combined ADC values of malignant fractures were significantly lower than those of benign ones on DWI with a b value of 300 s/mm² (t = 9.097, p < 0.01). Four cases of benign vertebral fractures were misdiagnosed as being malignant when b values of 0 s/mm² and 100 s/mm² were used. Conclusions When DWI with multiple b values is used to differentiate benign from malignant vertebral compression fractures, b values within the range of around 300 s/mm² are recommended, taking into account both SNR and diffusion weighting of water molecules.     

Rapid echoplanar diffusion imaging in a case of variant Creutzfeldt-Jakob disease; where speed is of the essence

Neuroimaging with magnetic resonance imaging (MRI) is important in the diagnosis of Creutzfeldt-Jakob disease (CJD), but is frequently frustrated by patient movement. Diffusion-weighted imaging (DWI) has previously shown markedly restricted diffusion in grey matter structures of patients with CJD, and may add to diagnostic sensitivity. Echoplanar imaging (EPI) sequences, which are usually used for DWI, are also very rapid, and typically allow imaging of the whole brain in less than 1 min. A case of histologically proven variant CJD (vCJD) in which conventional MRI was difficult to interpret confidently owing to motion artefact, but EPI was diagnostic, emphasises the utility of rapid imaging in agitated patients. Comparison of the regional quantitative apparent diffusion coefficient (ADC) with a control group (n=5) showed restricted diffusion in the caudate (vCJD: 0.63×10^–3 mm²/s; controls: mean 0.722×10^–3 mm²/s, SD 0.017) and lentiform (vCJD: 0.65×10^–3 mm²/s; controls: mean 0.707×10^–3 mm²/s, SD 0.011) nuclei. T2 effects dominated the signal abnormality on DWI in the pulvinar; ADC was increased (vCJD: 0.87–0.95×10^–3 mm²/s; controls: mean 0.773×10^–3 mm²/s, SD 0.038). Our data emphasise variation in diffusion patterns in vCJD, and illustrate the value in using all the components available from the DWI examination for maximum diagnostic information. EPI-DWI provides both rapid T2- and diffusion-dependent information, and is recommended for those patients in whom confusion and agitation is likely to confound standard MRI protocols.     

A comparative evaluation of a RARE-based single-shot pulse sequence for diffusion-weighted MRI of musculoskeletal soft-tissue tumors

The purpose of this study was to evaluate the feasibility of a centric-reordered modified rapid acquisition with relaxation enhancement (mRARE) sequence for single-shot diffusion-weighted magnetic resonance imaging (DWI) of soft-tissue tumors in the musculoskeletal system. In the evaluation of this sequence, DWI was performed in a liquid phantom, in excised human tumor samples embedded in bovine muscle, and in nine patients suffering from different types of soft-tissue tumors. The measurements were compared to DWI using a spin-echo sequence and a single-shot echo planar imaging (EPI) sequence. The phantom measurements in water and dimethyl sulfoxide showed a difference of less than 5% when comparing the apparent diffusion coefficients (ADCs) determined by the mRARE sequence and the two other techniques. Comparing mRARE and EPI, the differences in the ADCs were about 10% in the excised tumor tissue and, typically, about 15% in vivo. ADCs between 0.8×10^–3 mm²/s and 1.4×10^–3 mm²/s, depending on the tumor type, were found in solid tumor tissue; in cystic tumor areas, ADCs greater than 2.0×10^–3 mm²/s were determined with the mRARE and the EPI sequences. Diffusion-weighted images of the mRARE sequence were less distorted than those acquired with the single-shot EPI sequence, and provided more anatomic information, since the muscle and fat signals were considerably higher.     

Apparent diffusion coefficient in cervical cancer of the uterus: comparison with the normal uterine cervix

A relation between apparent diffusion coefficient (ADC) values and tumor cellular density has been reported. The purpose of this study was to measure the ADC values of cervical cancers in the uterus and compare them with those of normal cervical tissues, and to test whether ADC could differentiate between normal and malignant cervical tissues in the uterus. Twelve consecutive female patients with cervical cancer of the uterus and ten female patients with other pelvic abnormalities were included in this study. ADC was measured at 1.5 T with b-factors of 0, 300 and 600 s/mm² using single-shot echo-planar diffusion-weighted imaging and a parallel imaging technique. The mean ADC value of cervical cancer lesions was 1.09±0.20×10^–3 mm²/s, and that of normal cervix tissue was 1.79±0.24×10^–3 mm²/s (P<0.0001). In nine patients treated by chemotherapy and/or radiation therapy, the mean ADC value of the cervical cancer lesion increased significantly after therapy (P<0.001). The present study showed, with a small number of patients, that ADC measurement has a potential ability to differentiate between normal and cancerous tissue in the uterine cervix. Further study is necessary to determine the accuracy of ADC measurement in monitoring the treatment response.     

Evaluation of CT findings for diagnosis of pleural effusions

Computed tomography studies are usually used to assess patients with pleural effusions, and radiologists should be aware of the significance of different CT findings for the diagnosis of the effusion. The purpose of this study was to evaluate CT findings for etiological diagnosis of pleural effusions. Contrast-enhanced CT of the chest of 211 patients with pleural effusion of definite diagnosis were evaluated. The CT images were evaluated for the presence and extent of pleural effusion, thickening or nodules, extrapleural fat and other changes in the mediastinum or lung. The CT scans were read by two independent observers and correlation between them was evaluated. Comparison of CT findings between benign and malignant effusions, between exudates and transudates, and between empyemas and the other parapneumonic effusions were carried out. Kappa values for most CT findings were > 0.85. Loculation, pleural thickening, pleural nodules, and extrapleural fat of increased density were only present in exudative effusions. Multiple pleural nodules and nodular pleural thickening were the only pleural findings limited to malignant pleural effusions. The signs were also more frequently seen in empyemas than in other parapneumonic effusions. Computed tomography findings can help to distinguish between transudates and exudates. Although there is some overlap between benign and malignant pleural effusions, pleural nodules and nodular pleural thickening were present almost exclusively in the latter. Although differences between CT findings of empyemas and the other parapneumonic effusions exist, there is no finding which can definitely differentiate between them. Received: 27 January 1999; Revised: 24 June 1999; Accepted: 24 August 1999     

Apparent diffusion coefficient values of cryptorchid testes and malignant transformation of cryptorchidism (MTC) (seminoma) in postpubertal patients

Objectives:Diffusion-weighted imaging signal contrast can be quantified by apparent diffusion coefficient (ADC) maps, which reflect the diffusion properties of the examined tissue and are helpful for identifying pathology. To determine ADC values of cryptorchid testes in post-pubertal patients and assess performance for characterizing cryptorchid testes.Methods:The medical records from 35 patients with unilateral scrotal vacuity were retrospectively reviewed. Data were analyzed in three groups: Group A, normal testes (i.e. the contralateral testes of the patients with cryptorchidism or MTC); Group B, cryptorchid testes; and Group C, malignant transformation of cryptorchidism (MTC) (seminoma). DWI used b-values of 0 and 800 s/mm². Mean ADC values were compared using the independent samples t-test. The ability of ADC values was assessed using receiver operating characteristic curve analysis. The sensitivity, specificity, and accuracy were calculated.Results:Mean ADC values for normal testes, cryptorchid testes, and MTC were 1.18 ± 0.18×10⁻³ mm²/s, 1.82 ± 0.40×10⁻³ mm²/s, and 0.80 ± 0.06×10⁻³ mm²/s, respectively. There were statistically significant differences in mean ADC values between normal testes and cryptorchid testes or MTC (p < 0.001). The cut-off ADC value for differentiating normal testes from cryptorchid testes was 1.47 × 10⁻³ mm²/s. The sensitivity, specificity, and accuracy were 88%, 91%, and 90%, respectively. The cut-off ADC value for differentiating normal testes from MTC was 1.22 × 10⁻³ mm²/s. The sensitivity, specificity, and accuracy were 100%, 31%, and 43%, respectively.Conclusion:ADC values of cryptorchid testes may be used to inform clinical decision-making and also monitor testicular function in patients who retain undescended testicles or post-operatively.Advances in knowledge:Mean ADC values of cryptorchidism and MTC (seminoma) were used to reflect their pathological features.     

Diffusion-weighted MRI of soft tissue tumours

The purpose of this study was to evaluate the clinical utility of a multi-shot spin-echo echo-planar (SE-EPI) diffusion-weighted sequence in the diagnostic work-up of soft tissue tumours. There were 29 patients, 16 with a benign lesion and 13 with a sarcoma. Four of the sarcomas were examined both before and after radiation therapy. Diffusion-weighted imaging was performed with a multi-shot SE-EPI sequence. The b values were 0 and 600 s/mm². Phase navigation and pulse trigging were applied. The apparent diffusion constant (ADC) value of a large region of interest (ROI) representing the lesion was measured and compared to diagnosis and treatment. The ADC values of the benign lesions (mean 1.8×10^–3 mm²/s) overlapped with non-treated sarcomas (mean 1.7×10^–3 mm²/s). The ADC value increased in all radiated sarcomas. A multi-shot SE-EPI diffusion imaging sequence of less than 2-min duration is technically feasible in soft tissue tumours of the extremities and the trunk. The ADC values of benign soft tissue tumours and sarcomas overlapped and could not be used to differentiate between the bulk of benign and malignant tumours. However, the increase in ADC values of soft tissue sarcomas after radiotherapy warrants further studies of diffusion imaging for evaluating therapy response.     

Reproducibility of measurement of apparent diffusion coefficients of malignant hepatic tumors: Effect of DWI techniques and calculation methods

Purpose:

To evaluate the effect of diffusion‐weighted imaging (DWI) methods, apparent diffusion coefficient (ADC) calculation methods, and selection of b‐values on the ADCs and the measurement reproducibility of malignant hepatic tumors.

Materials and Methods:

Nineteen patients with pathologically confirmed malignant hepatic tumors underwent breath‐hold DWI (b‐values = 0, 50, 500 s/mm²) and respiratory‐triggered DWI (0, 50, 300, 500, 1000 s/mm²) twice on a 1.5 T magnetic resonance imaging (MRI) scanner. ADCs were calculated using a two b‐value and/or a multiple b‐value method. The reproducibility of the ADC measurements was evaluated from the intraclass correlation coefficients (ICCs) and the 95% Bland–Altman limit‐of‐agreement (LOA).

Results:

The ADCs were different according to the DWI methods (P = 0.040–0.282), ADC calculation methods (P = 0.003–0.825), and the choice of b‐values (P < 0.001). The ADC tended to be more reproducible with use of breath‐hold DWI (ICC: 0.898–0.933; LOA, 18.8%–24.0%) than respiratory‐triggered DWI (ICC: 0.684–0.928; LOA, 15.0%–31.9%) (P = 0.008–0.122). For respiratory‐triggered DWI, the multiple b‐value method using five b‐values had better reproducibility than the two b‐value method for measurement of ADC (P = 0.009–0.221).

Conclusion:

The DWI method, ADC calculation method, and selection of b‐values potentially influence the ADCs and the reproducibility of malignant hepatic tumors. ADCs calculated from breath‐hold DWI are more reproducible than from respiratory‐triggered DWI. A multiple b‐value method may improve the reproducibility of respiratory‐triggered DWI. J. Magn. Reson. Imaging 2012;36:1131–1138. © 2012 Wiley Periodicals, Inc.     

Bilateral parapneumonic pleural effusion with pneumothorax in a patient with covid 19 pneumonia: case report

Recurrent pyogenic effusion combined with bilateral pneumothorax is a rare complication associated with the COVID−19 infection. Current article presents the case report of a 68-year-old male with the severe community-acquired bilateral polysegmental viral COVID−19 pneumonia. Chest radiography on the 15th day after admission to the hospital showed the presence of air and pleural effusion in the right pleural cavity with collapse of the right lung. Thoracentesis and thoracostomy in the sixth intercostal space on the mid-axillary line were performed. About 1400 ml of a yellowish opaque liquid were evacuated from the pleural cavity. Pleural fluid analysis confirmed an exudative lymphocytic-rich effusion with no growth of acid-fast bacteria (AFB). In the pleural fluid such gram-negative bacteria as Acinetobacter baumannii and Pseudomonas aeruginosa were cultured. Chest computed tomography obtained on the third day after thoracentesis showed radiological sings of bilateral hydropneumothorax. Needle thoracocentesis and new pleural drainage in the second intercostal space on the right midclavicular line were established. Five days later after the second drainage of the pleural space was initiated the patient was diagnosed with pleural empyema and transferred to the Surgical Clinic. This case report highlights that in patients with COVID-19 recurrent pyogenic effusion combined with bilateral pneumothorax may occur.     

The role of MR diffusion in differentiation of malignant and benign hepatic focal lesions

Aim

To determine if focal liver masses could be differentiated as benign or malignant by DWI and ADC maps.

Methods and materials

Sixty focal liver lesions were scanned using 1.5 T MRI. DWI was performed with b 0, b 500 and b 1000 gradients with ADC measurements. Comparison of mean ADC values between each benign and malignant lesion was done. Reference standard of diagnosis was obtained by correlating DWI with histopathologic findings and imaging follow-up. The accuracies of DWI and ADC values were assessed with the Student’s t test, and cut-off values were determined with receiver operating characteristic curve analysis.

Results

When ADC value of 1.0 × 10⁻³ mm²/s was used as a threshold value for differentiation of malignant tumors from benign lesions, sensitivity was 90.3%, specificity 78.57% and accuracy 86.7%. The best result was obtained with the use of ADC cut off value (at b 500) of 1.5 × 10⁻³ mm²/s and ADC cut off value (at b 1000) of 1.0 × 10⁻³ mm²/s, with 90.3% sensitivity, 92.86% specificity, 91.1% accuracy, 96.6% positive predictive value and 81.3% negative predictive value.

Conclusion

DWI and ADC map is a useful tool in differential diagnosis of malignant from benign liver lesions.     

Differentiation of benign and malignant lesions of the tongue by using diffusion-weighted MRI at 3.0?T

Objectives:

Diffusion-weighted MRI (DWI) has been introduced in head and neck lesions and adds important information to the findings obtained through conventional MRI. The purpose of this study was to assess the role of DWI in differentiating benign and malignant lesions of the tongue at 3.0-T field strength imaging.

Methods:

78 patients with 78 lingual lesions underwent conventional MRI and DWI with b-values of 0 and 1000 s mm⁻² before therapy. The apparent diffusion coefficient (ADC) maps were reconstructed, and the ADC values of the lingual lesions were calculated and compared between benign and malignant lesions of the tongue.

Results:

The mean ADC values of the malignant tumours, benign solid lesions and cystic lesions were (1.08 ± 0.16) × 10⁻³, (1.68 ± 0.33) × 10⁻³ and (2.21 ± 0.35) × 10⁻³ mm² s⁻¹, respectively. The mean ADC values of malignant tumours were significantly lower (p < 0.001) than those of benign solid lesions, and the mean ADC values of benign solid lesions were significantly lower (p < 0.001) than those of cystic lesions. Receiver operating characteristic analysis showed that when an ADC value <1.31 × 10⁻³ mm² s⁻¹ was used for predicting malignancy, the highest accuracy of 95.3%, sensitivity of 92.6% and specificity of 97.3% were obtained.

Conclusions:

ADC values of benign and malignant lesions are significantly different at 3.0-T imaging. DWI can be applied as a complementary tool in the differentiation of benign and malignant lesions of the tongue.     

Diffusion‐weighted imaging of the liver: Comparison of navigator triggered and breathhold acquisitions

Purpose

To compare a free breathing navigator triggered single shot echoplanar imaging (SS EPI) diffusion‐weighted imaging (DWI) sequence with prospective acquisition correction (PACE) with a breathhold (BH) DWI sequence for liver imaging.

Materials and Methods

Thirty‐four patients were evaluated with PACE‐DWI and BH DWI of the liver using b‐values of 0, 50, and 500 s/mm². There were 29 focal liver lesions in 18 patients. Qualitative evaluation was performed on a 3‐point scale ( 1 - 3 ) by two independent observers (maximum score 9). Quantitative evaluation included estimated SNR (signal to noise ratio), lesion‐to‐liver contrast ratio, liver and lesion apparent diffusion coefficients (ADCs), and coefficient of variation (CV) of ADC in liver parenchyma and focal liver lesions (estimate of noise contamination in ADC).

Results

PACE‐DWI showed significantly better image quality, higher SNR and lesion‐to‐liver contrast ratio when compared with BH DWI. ADCs of liver and focal lesions with both sequences were significantly correlated (r = 0.838 for liver parenchyma, and 0.904 for lesions, P < 0.0001), but lower with the BH sequence (P < 0.02). There was higher noise contamination in ADC measurement obtained with BH DWI (with a significantly higher SD and CV of ADC).

Conclusion

The use of a navigator echo to trigger SS EPI DWI improves image quality and liver to lesion contrast, and enables a more precise ADC quantification compared with BH DWI acquisition. J. Magn. Reson. Imaging 2009;30:561–568. © 2009 Wiley‐Liss, Inc.     

Diffusion-Weighted Imaging of the Head and Neck in Healthy Subjects: Reproducibility of ADC Values in Different MRI Systems and Repeat Sessions

BACKGROUND AND PURPOSE:DWI is typically performed with EPI sequences in single-center studies. The purpose of this study was to determine the reproducibility of ADC values in the head and neck region in healthy subjects. In addition, the reproducibility of ADC values in different tissues was assessed to identify the most suitable reference tissue.MATERIALS AND METHODS:We prospectively studied 7 healthy subjects, with EPI and TSE sequences, on 5 MR imaging systems at 3 time points in 2 institutions. ADC maps of EPI (with 2 b-values and 6 b-values) and TSE sequences were compared. Mean ADC values for different tissues (submandibular gland, sternocleidomastoid muscle, spinal cord, subdigastric lymph node, and tonsil) were used to evaluate intra- and intersubject, intersystem, and intersequence variability by using a linear mixed model.RESULTS:On 97% of images, a region of interest could be placed on the spinal cord, compared with 87% in the tonsil. ADC values derived from EPI-DWI with 2 b-values and calculated EPI-DWI with 2 b-values extracted from EPI-DWI with 6 b-values did not differ significantly. The standard error of ADC measurement was the smallest for the tonsil and spinal cord (standard error of measurement = 151.2 × 10⁻⁶ mm/s² and 190.1 × 10⁻⁶ mm/s², respectively). The intersystem difference for mean ADC values and the influence of the MR imaging system on ADC values among the subjects were statistically significant (P < .001). The mean difference among examinations was negligible (ie, <10 × 10⁻⁶ mm/s²).CONCLUSIONS:In this study, the spinal cord was the most appropriate reference tissue and EPI-DWI with 6 b-values was the most reproducible sequence. ADC values were more precise if subjects were measured on the same MR imaging system and with the same sequence. ADC values differed significantly between MR imaging systems and sequences.

Almost 3% of all malignancies are head and neck cancer, 95% of which are squamous cell carcinomas.¹ MR imaging is one of the modalities used in the work-up of patients with head and neck cancer.² DWI is an MR imaging technique by which diffusion properties of water can be quantified as an ADC value.³ Changes in ADC are inversely correlated with changes in cellularity.⁴ In tissues with high cellularity, diffusion of extracellular water in particular is limited by cell membranes, which give low ADC values. In tissues with low cellularity, when diffusion is facilitated (eg, in edematous or necrotic tissue), ADC values are high.Indications for DWI in head and neck cancer include tissue characterization of primary tumors and nodal metastases, prediction and monitoring of treatment response after chemotherapy or radiation therapy, and differentiation of radiation changes and residual or recurrent disease.⁵Neither the optimal DWI sequence for assessment of the head and neck region nor its reproducibility has been clearly established, to our knowledge. DWI can be performed with either EPI or TSE sequences, of which the EPI sequence is most commonly used in the head and neck area.^6,7 On EPI-DWI, more malignant lesions can be detected and lesion delineation is facilitated. However, the interobserver agreement of ADC values is reported to be higher on TSE-DWI, probably due to the frequent occurrence of artifacts and geometric distortions in EPI-DWI.⁸Currently the use of DWI in head and neck imaging is mostly confined to research protocols and advanced academic centers. Before DWI can be used in multicenter studies, its reproducibility across different centers and MR imaging systems should be validated.⁹ ADC values may be affected by the selected technique and MR imaging system (eg, due to differences in gradient systems, coils, pulse-sequence designs, imaging parameters, and artifacts related to susceptibility effects or eddy currents).¹⁰ Information on variance is needed.¹¹ Furthermore, the use of reference tissues might help ascertain the variability among different MR imaging systems and could potentially help correct for differences in ADC values among MR imaging systems.The purpose of this prospective study was to determine the reproducibility of ADC values in the head and neck region obtained from DWI on the basis of both EPI and TSE sequences in repeated measurement on different MR imaging systems in healthy subjects. In addition, we assessed which tissue shows the highest reproducibility in ADC values, so that it could function as a reference tissue in future studies.     

Pancreatic diffusion‐weighted imaging (DWI): Comparison between mass‐forming focal pancreatitis (FP), pancreatic cancer (PC), and normal pancreas

Purpose

To compare diffusion‐weighted imaging (DWI) findings and the apparent diffusion coefficient (ADC) values of pancreatic cancer (PC), mass‐forming focal pancreatitis (FP), and the normal pancreas.

Materials and Methods

DWI (b = 0 and 600 seconds/mm²) findings of 14 patients with mass‐forming FP proven by histopathology and or clinical follow‐up, 10 patients with histopathologically‐proven PC, and 14 subjects with normal pancreatic exocrine function and normal imaging findings were retrospectively evaluated. ADC values of the masses, the remaining pancreas, and the normal pancreas were measured.

Results

On b = 600 seconds/mm² DWI, mass‐forming FP was visually indistinguishable from the remaining pancreas whereas PC was hyperintense relative to the remaining pancreas. The mean ADC value of PC (1.46 ± 0.18 mm²/second) was significantly lower than the remaining pancreas (2.11 ± 0.32 × 10^–3 mm²/second; P < 0.0001), mass‐forming FP (2.09 ± 0.18 × 10^–3 mm²/second; P < 0.0001), and pancreatic gland in the control group (1.78 ± 0.07 × 10^–3 mm²/second; P < 0.0005). There was no significant difference of ADC values between the mass‐forming focal pancreatitis and the remaining pancreas (2.03 ± 0.2 × 10^–3 mm²/second; P > 0.05).

Conclusion

Differences on DWI may help to differentiate PC, mass‐forming FP, and normal pancreas from each other. J. Magn. Reson. Imaging 2009;29:350–356. © 2009 Wiley‐Liss, Inc.