Characterization and evolution of diffusion MR imaging abnormalities in stroke patients undergoing intra-arterial thrombolysis

BACKGROUND AND PURPOSE: Lesions revealed by pretreatment diffusion-weighted imaging (DWI) may not progress to infarction, and apparent diffusion coefficient (ADC) or DWI thresholds for tissue viability may exist. We evaluated the evolution of abnormal DWI findings in patients with acute stroke who underwent thrombolysis. METHODS: Sixteen patients with acute occlusion of the anterior circulation underwent DWI followed by intra-arterial thrombolysis; follow-up CT or MR imaging was performed after reperfusion therapy. Lesion volumes were measured on all images. In three patients with abnormal DWI findings that appeared normal at follow-up, ADC values, ADC ratios, and DWI ratios were obtained on a section-by-section basis in the DWI-hyperintense regions that were either abnormal or normal at follow-up. RESULTS: In three patients, part of the DWI-hyperintense tissue appeared normal and part appeared abnormal at follow-up imaging. In one of these patients, the lesion decreased by -35.6%. In the other two, lesion growth appeared in regions that appeared normal at initial DWI: in one, the overall change in size was -2.4%, and in the other, the lesion increased by 89.8%. Respective mean changes at follow-up in normal-appearing and abnormal-appearing regions were: ADC, 731.7 x 10(-6) mm(2)/s and 650.4 x 10(-6) mm (2)/s; ADC ratio, 0.92 and 0.78; and DWI ratio, 1.16 and 1.32 (P <.001 for all measures). CONCLUSION: In patients with acute stroke who undergo intra-arterial thrombolysis, most abnormal, pretreatment DWI findings indicate eventual infarction. In 19% of the patients described herein, DWI-hyperintense regions appeared normal at follow-up. ADC values, ADC ratios, and DWI ratios may be useful in identifying the portion of abnormal tissue that is potentially salvageable after reperfusion therapy.     

液体衰减反转恢复脉冲对DWI图像信噪比及ADC值的影响

目的:探讨液体衰减反转恢复(FLAIR)脉冲序列对扩散加权图像(DWI)信噪比及ADC值的影响.方法:17名健康志愿者在3.0T MRI上行常规轴位DWI和FIAIR-DWI扫描,分别测量两侧半卵圆区、扣带回、丘脑及胼胝体膝部和压部的ADC值及DWI信号强度,同时测量基底节层面的DWI信号强度作为噪声,计算以上5个部位DWI图像的信噪比.结果:扣带回和胼胝体压部的ADC值在施加FLAIR脉冲后显著下降,而半卵圆区、丘脑及胼胝体膝部在施加FLAIR脉冲前后无明显变化;5个部位的DWI图像信噪比在施加FLAIR脉冲后均显著下降(P＜0.01).结论:FLAIR显著提高了脑组织和脑脊液ADC值测量的准确性,但是也明显降低了DWI图像的信嗓比.     

Influence of fluid-attenuated inversion-recovery on stroke apparent diffusion coefficient measurements and its clinical application

Background and purpose

The application of a fluid-attenuated inversion-recovery pulse with a conventional diffusion-weighted MRI sequence (FLAIR DWI) decreases the partial volume effects from cerebrospinal fluid on apparent diffusion coefficient (ADC) measurements. For this reason, FLAIR DWI may be more useful in the evaluation of ischemic stroke, but few studies have looked at the effect of FLAIR on ADC measurements in this setting. This study quantitatively compares FLAIR DWI and conventional DWI in ischemic stroke of varying ages to assess the potential advantages of this technique.

Methods

We respectively analyzed 139 DWI studies in patients with ischemic stroke with and without FLAIR at varying time points ranging from hyperacute to chronic. ADC values were measured in each lesion, as well as in the contralateral normal side. Comparisons were made between the ADC values obtained from the DWI sequences with and without FLAIR for both the lesion and the normal contralateral side.

Results

The ADC measurements within the ischemic lesion were very similar on FLAIR DWI and conventional DWI for lesions less than 14 days old (p > 0.05), but were significantly decreased on FLAIR DWI for lesions between 15 and 30 days old and in lesions >31 days old (chronic stage) (p < 0.01). The contralateral ADC values were all significantly decreased on the FLAIR DWI sequence compared with conventional DWI (p < 0.01).

Conclusions

The application of an inversion pulse does not significantly affect the ADC values for early stage ischemic stroke (less than 14 days from symptom onset), but results in a more accurate relative ADC measurement by reducing the cerebrospinal fluid partial volume effects of the normal contralateral side. In addition, combined with the conventional DWI, FLAIR DWI may be helpful in determining the age of ischemic lesions.     

液体衰减反转恢复预脉冲序列在缺血性脑梗死表观扩散系数值定量研究中的价值

目的 探讨液体衰减反转恢复(FLAIR)序列预脉冲对缺血性脑梗死ADC值的影响及其临床应用价值.方法 回顾性分析139例次脑梗死的常规DWI和FLAIR-DWI资料,采用配对t检验的方法分别比较不同发病时间段的梗死病灶的常规ADC值(ADCCON)和FLAIR ADC值(ADCFLAIR).再根据梗死病灶是否累及大脑皮层将所有病灶分为皮层梗死组、皮层下梗死组,同样的方法比较皮层梗死组、皮层下梗死组以及对侧正常脑组织(对照组)ADCCON和ADCFLAIR值.结果 梗死病灶的平均ADCCON和ADCFLAIR值在发病0～6 h、7～12 h、13～24 h、2 d、3～4 d,5～7 d及8～14 d[ADCCON值分别为(0.55±0.07)、(0.50±0.09)、(0.50±0.13)、(0.50±0.13)、(0.62±0.14)、(0.60±0.12)、(0.72±0.20)×10-3mm2/s;ADCFLAIR值分别为(0.53±0.09)、(0.49±0.06)、(0.49±0.10)、(0.48±0.08)、(0.58±0.14)、(0.60±0.09)、(0.73±0.15)×10-3mm2/s]各个阶段差异均无统计学意义(P值均>0.05),发病15～30 d和31 d以上的病灶其ADCFLAIR值均低于ADCCON[15～30 d组ADCFLAIR和ADCCON分别为(0.95±0.21)、(1.02±0.27)×10-3mm2/s,31 d以上组分别为(1.10±0.30)、(1.36±0.41)×10-3 mm2/s],差异均有统计学意义(P值均<0.01);14 d以内的皮层梗死组和皮层下梗死组的ADCCON值[分别为(0.55±0.16)、(0.61±0.14)×10-3 mm2/s]与ADCFLAIR值[分别为(0.53±0.14)、(0.60±0.13)×10-3mm2/s]差异均无统计学意义(P值均>0.05);14 d以后ADCCON值则高于ADCFLAIR[皮层梗死组ADCCON和ADCFLAIR分别为(1.35±0.48)、(1.16±0.36)×10-3mm2/s,皮层下梗死组分别为(1.15±0.33)、(0.97±0.19)×10-3mm2/s],差异均有统计学意义(P值均<0.01);病灶对侧正常对照脑组织的ADCFLAIR值[(0.76±0.05)×10-3 mm2/s]低于ADCCON[(0.82±0.11)×10-3 mm2/s],差异具有统计学意义(P<0.01).结论 FLAIR预脉冲序列显著减低发病14 d后的脑梗死组织ADC值,这对于个体患者的脑梗死期龄的判断有帮助;同时FLAIR预脉冲能够通过减少自由水对正常脑组织ADC值的影响,从而增强相对ADC值检测细微缺血损伤的能力.     

Diffusion-weighted imaging of the spine with a non-carr-purcell-meiboom-gill single-shot fast spin-echo sequence: initial experience

BACKGROUND AND PURPOSE: To prospectively evaluate the signal-to-noise ratio (SNR) improvement in diffusion-weighted imaging (DWI) of the spine with the use of a newly developed non-Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo (SS-FSE) sequence and its effect on apparent diffusion coefficient (ADC) measurements. MATERIALS AND METHODS: Twenty-four patients were enrolled after written informed consent. DWI of the spine was obtained with an echo-planar imaging (EPI)-based sequence followed by a non-CPMG SS-FSE technique. SNR and ADC values were measured over a lesion-free vertebral corpus. A quality score was assigned for each set of images to assess the image quality. When a spinal lesion was present, contrast-to-noise ratio (CNR) and ADC were also measured. Student t tests were used for statistical analysis. RESULTS: Mean SNR values were 5.83 +/- 2.2 and 11.68 +/- 2.87 for EPI and non-CPMG SS-FSE DWI, respectively. SNR values measured in DWI using parallel imaging were found to be significantly higher (P < .01). Mean ADCs of the spine were 0.53 +/- 0.15 and 0.35 +/- 0.15 x 10(-3) mm(2)/s for EPI and non-CPMG SS-FSE DWI, respectively. Quality scores were found to be higher for the non-CPMG SS-FSE DWI technique (P < .05). Overall lesion CNR was found to be higher in DWI with non-CPMG SS-FSE. CONCLUSION: The non-CPMG SS-FSE technique provides a significant improvement to current EPI-based DWI of the spine. A study including a larger number of patients is required to determine the use of this DWI sequence as a supplementary tool to conventional MR imaging for increasing diagnostic confidence in spinal pathologic conditions.     

Chronic cystic lesion of the sacrum: characterisation with diffusion-weighted MR imaging

PURPOSE: Sacral bone remodelling with abnormal dilatation of intervertebral foramina is usually associated with Tarlov cysts but can be caused by slow-growth lesions, which also may present cerebrospinal-fluid (CSF)-like signal or density. We describe three patients with a similar history of lower back pain presenting CSF-like density/signal lesions with extensive sacral bone remodelling who were affected by a Tarlov cyst, an epidermoid cyst and a giant neurofibroma, respectively. MATERIALS AND METHODS: Magnetic resonance imaging (MRI) studies were performed with 1.0-T magnet; axial and sagittal pre- and postcontrast T1-and T2-weighted images were obtained. Moreover, axial and sagittal diffusion-weighted (DWI) echoplanar images were produced, and corresponding apparent diffusion coefficient (ADC) values were calculated. ADC values were measured within the lesions on axial images. RESULTS: All lesions presented a CSF-like signal on conventional MRI. The Tarlov cyst was hypointense on DWI with high ADC values (2,793 s/mm(2)+/-137). The epidermoid cyst proved to be markedly hyperintense on DWI, with reduced ADC values (855 s/mm(2)+/-109). The neurofibroma was isointense on DWI, with ADC values not compatible with CSF (1,467 s/mm(2)+/-130). CONCLUSIONS: DWI and ADC values seem to be able to clearly differentiate Tarlov cysts from slow-growth lesions, allowing for adequate treatment.     

Single breath-hold diffusion-weighted MRI of the liver with parallel imaging: initial experience

AIM: To evaluate prospectively the improvement in the signal:noise ratio (SNR), with the use of parallel technique in single breath-hold diffusion-weighted imaging (DWI) of the liver and its affect on apparent diffusion coefficient (ADC) measurements. MATERIALS AND METHODS: This study was approved by our institutional review board. Written informed consent was obtained from all participants. Fifteen patients underwent single breath-hold DWI of the liver with and without parallel imaging technique. SNR and ADC values were measured over a lesion-free right hepatic lobe by two radiologists in both series. When a focal hepatic lesion was present the contrast:noise ratio (CNR) and ADC were also measured. Paired Student's t-tests were used for statistical analysis. RESULTS: Mean SNR values of the liver were 20.82+/-7.54 and 15.83+/-5.95 for DWI with and without parallel imaging, respectively. SNR values measured in DWI using parallel imaging were found to be significantly higher (p<0.01). Mean ADC of the liver were 1.61+/-0.45 x 10(-3)mm(2)/s and 1.56+/-0.28 x 10(-3)mm(2)/s for DWI with and without parallel imaging, respectively. No significant difference was found between the two sequences for hepatic ADC measurement (p>0.05). Overall lesion CNR was found to be higher in DWI with parallel imaging. CONCLUSION: Parallel imaging is useful in improving SNR of single breath-hold DWI of the liver without compromising ADC measurements.     

Evolution of apparent diffusion coefficient, diffusion-weighted, and T2-weighted signal intensity of acute stroke

BACKGROUND AND PURPOSE: Serial study of such MR parameters as diffusion-weighted imaging (DWI), apparent diffusion coefficient (ADC), ADC with fluid-attenuated inversion recovery (ADC(FLAIR)), and T2-weighted imaging may provide information on the pathophysiological mechanisms of acute ischemic stroke. Our goals were to establish the natural evolution of MR signal intensity characteristics of acute ischemic lesions and to assess the potential of using specific MR parameters to estimate lesion age. METHODS: Five serial echo-planar DWI studies with and without an inversion recovery pulse were performed in 27 patients with acute stroke. The following lesion characteristics were studied: 1) conventional ADC (ADC(CONV)); 2) ADC(FLAIR); 3) DWI signal intensity (SI(DWI)); 4) T2-weighted signal intensity (SI(T2)), and 5) FLAIR signal intensity (SI(FLAIR)). RESULTS: The lesion ADC(CONV) gradually increased from low values during the first week to pseudonormal during the second week to supranormal thereafter. The lesion ADC(FLAIR) showed the same pattern of evolution but with lower absolute values. A low ADC value indicated, with good sensitivity (88%) and specificity (90%), that a lesion was less than 10 days old. All signal intensities remained high throughout follow-up. SI(DWI) showed no significant change during the first week but decreased thereafter. SI(T2) initially increased, decreased slightly during week 2, and again increased after 14 days. SI(FLAIR) showed the same initial increase as the SI(T2) but remained relatively stable thereafter. CONCLUSION: Our findings further clarify the time course of stroke evolution on MR parameters and indicate that the ADC map may be useful for estimating lesion age. Application of an inversion recovery pulse results in lower, potentially more accurate, absolute ADC values.     

Detection of lymph node metastasis in cervical and uterine cancers by diffusion-weighted magnetic resonance imaging at 3T

PURPOSE: To evaluate diffusion-weighted imaging (DWI) for detection of pelvic lymph node metastasis in patients with cervical and uterine cancers. MATERIALS AND METHODS: Fifty patients scheduled for pelvic lymph node dissection were enrolled for 3T magnetic resonance imaging (MRI) using a single-shot echo-planar DWI technique, body-phased array coil, b = 0, 1000 s/mm(2). We measured short/long-axis diameters, mean apparent diffusion coefficient (ADC) values of all identifiable nodes, relative ADC values between tumors and nodes, and utilized their cutoff values to validate the diagnostic accuracy internally. Histopathologic results served as the reference standard. RESULTS: The relative ADC values between tumor and nodes were significantly lower in metastatic than in benign nodes (0.06 vs. 0.21 x 10(-3) mm(2)/s, P < 0.001; cutoff value 0.10 x 10(-3) mm(2)/s). Compared to conventional MRI, the method combining size and relative ADC values resulted in better sensitivity (25% vs. 83%) and similar specificity (98% vs. 99%). The smallest metastatic lymph node detected by this method measured 5 mm on its short axis. CONCLUSION: The combination of size and relative ADC values was useful in detecting pelvic lymph node metastasis in patients with cervical and uterine cancers.     

Persistent high signal on diffusion-weighted MRI in the late stages of small cortical and lacunar ischaemic lesions

Diffusion-weighted imaging (DWI) is very sensitive to early brain infarcts. However, the late stages have been insufficiently studied. Infarcts in small vessel disease are often multiple and of different ages, and differentiation between new and old lesions might be difficult. We have therefore studied the change with time in DWI of small (< 3 ml) ischaemic lesions. We imaged 21 patients with an acute lacunar syndrome and a lesion visible on early DWI. They all had three MRI examinations 12-58 h (early), 7-16 and 54-144 days after the onset of stroke; 10 patients with high DWI signal on the third examination had a fourth examination 12-28 months after the stroke. MRI was performed at 1.5 T, using echo-planar DWI with 7 b-values from 0 to 1200 x 10(6) s/m2 and conventional T2-weighted imaging. After 7-16 days 18 of 21 lesions gave high signal on DWI, and 12/16 measurable lesions had a decreased apparent diffusion coefficient (ADC). After 54-144 days ten lesions still gave high DWI signal and two still had an ADC below normal. On the fourth examination there was no remaining high DWI signal and all ADC were higher than normal.     

Diffusion-weighted imaging of the prostate at 3 T for differentiation of malignant and benign tissue in transition and peripheral zones: preliminary results

OBJECTIVE: To evaluate prospectively the use of apparent diffusion coefficients (ADCs) for the differentiation of malignant and benign tissue in the transition (TZ) and peripheral (PZ) zones of the prostate diffusion-weighted imaging (DWI) at 3 T magnetic resonance imaging (MRI) using a phased-array coil. METHODS: The DWI at 3-T MRI was performed on a total of 35 patients before radical prostatectomy. A single-shot echo-planar imaging DWI technique with b = 0 and b = 1000 s/mm2 was used. The ADC values were measured in both benign and malignant tissues in the PZ and TZ using regions of interest. Differences between PZ and TZ ADC values were estimated using a paired Student t test. Presumed ADC cutoff values in the PZ and TZ for the diagnosis of cancer were assessed by receiver operating characteristic analysis. RESULTS: The ADC values of malignant tissues were significantly lower than those of benign tissues in the PZ and TZ (P < 0.001; 1.32 +/- 0.24 x 10(-3) mm2/s vs 1.97 +/- 0.25 x 10(-3) mm2/s, and 1.37 +/- 0.29 x 10(-3) mm2/s vs 1.79 +/- 0.19 x 10(-3) mm2/s, respectively). For tumor diagnosis, cutoff values of 1.67 x 10(-3) mm2/s (PZ) and 1.61 x 10(-3) mm2/s (TZ) resulted in sensitivities and specificities of 94% and 91% and 90% and 84%, respectively. CONCLUSIONS: The DWI of the prostate at 3T MRI using a phased-array coil was useful for the differentiation of malignant and benign tissues in the TZ and PZ.     

Diffusion-weighted MR imaging in Japanese encephalitis

OBJECTIVE: This study was performed to evaluate the role of diffusion-weighted imaging (DWI) in the diagnosis of Japanese encephalitis (JE) and to look for any relationship of the apparent diffusion coefficient (ADC) values with duration of the illness. METHODS: We performed DWI in fourteen patients of JE. T2 weighted (T2W) and DWI were compared for number and location of lesions in all patients. Based on imaging patients were divided in three groups: group 1 (n=9) showing more lesions on DWI compared with T2W images, group 2 (n=3) with equal number of lesions on T2W and DWI and group 3 (n=2) with lesions more pronounced on T2W than DWI. ADC values were computed for all the lesions. The time interval between onset of neurologic signs/symptoms and MRI were charted and correlated with ADC values. RESULTS: DWI was helpful in making early diagnosis of JE by showing characteristic involvement of bilateral thalami in four patients. Nine out of fourteen patients showed additional lesions on DWI. ADC from lesions in groups I, II and III measured 0.648 +/- 0.099 x 10 mm/s, 0.739 +/- 0.166 x 10 mm/s and 1.123 +/- 0.185 x 10 mm/s respectively. The ADC from the lesions in group 1 was significantly lower compared with group 2 (P value <0.05) while it was higher in group 3 lesions compared with the other two groups. There was a significant direct correlation of ADC values with the disease duration in these cases (r=0.847, P <0.01). CONCLUSIONS: DWI is helpful in early diagnosis and characterization of the duration of the lesions in JE.     

ADC mapping of benign and malignant breast tumors.

PURPOSE: The purpose of this study was to investigate the utility of diffusion-weighted imaging (DWI) and the apparent diffusion coefficient (ADC) value in differentiating benign and malignant breast lesions and evaluating the detection accuracy of the cancer extension. MATERIALS AND METHODS: We used DWI to obtain images of 191 benign and malignant lesions (24 benign, 167 malignant) before surgical excision. The ADC values of the benign and malignant lesions were compared, as were the values of noninvasive ductal carcinoma (NIDC) and invasive ductal carcinoma (IDC). We also evaluated the ADC map, which represents the distribution of ADC values, and compared it with the cancer extension. RESULTS: The mean ADC value of each type of lesion was as follows: malignant lesions, 1.22+/-0.31 x 10(-3) mm2/s; benign lesions, 1.67+/-0.54 x 10(-3) mm2/s; normal tissues, 2.09+/-0.27 x 10(-3) mm2/s. The mean ADC value of the malignant lesions was statistically lower than that of the benign lesions and normal breast tissues. The ADC value of IDC was statistically lower than that of NIDC. The sensitivity of the ADC value for malignant lesions with a threshold of less than 1.6 x 10(-3) mm2/s was 95% and the specificity was 46%. A full 75% of all malignant cases exhibited a near precise distribution of low ADC values on ADC maps to describe malignant lesions. The main causes of false negative and underestimation of cancer spread were susceptibility artifact because of bleeding and tumor structure. Major histologic types of false-positive lesions were intraductal papilloma and fibrocystic diseases. Fibrocystic diseases also resulted in overestimation of cancer extension. CONCLUSIONS: DWI has the potential in clinical appreciation to detect malignant breast tumors and support the evaluation of tumor extension. However, the benign proliferative change remains to be studied as it mimics the malignant phenomenon on the ADC map.     

Diffusion-weighted imaging of normal and malignant prostate tissue at 3.0T

PURPOSE: To measure the apparent diffusion coefficient (ADC) of normal and malignant prostate tissue at 3.0T using a phased-array coil and parallel imaging, and determine the utility of ADC values in differentiating tumor from normal peripheral zone (PZ). MATERIALS AND METHODS: ADC values were calculated for 49 patients (tumor and PZ) with evidence of prostate cancer. Additionally, for nine asymptomatic volunteers, ADC values were determined for apparently normal central gland and PZ. A single-shot EPI diffusion-weighted imaging (DWI) technique with b = 0 and 500 seconds/mm2 was employed. RESULTS: ADC values were significantly lower for tumor (1.38 +/- 0.32 x 10(-3) mm2/second) than for patient PZ (1.95 +/- 0.50 x 10(-3) mm2/second, P < 0.001) and volunteer PZ (1.60 +/- 0.25 x 10(-3) mm2/second, P = 0.031). A considerable overlap of ADC values was noted between patient tissue types. CONCLUSION: DWI of the prostate at 3.0T in conjunction with a phased-array coil and parallel imaging allows ADC calculation of the prostate. ADC values were lower for tumors compared to normal-appearing PZ; however, there was considerable intersubject variability.     

Evaluation of diffusion-weighted imaging for the differential diagnosis of poorly contrast-enhanced and T2-prolonged bone masses: Initial experience

PURPOSE: To determine whether quantitative diffusion-weighted imaging (DWI) is useful for characterizing poorly contrast-enhanced and T2-prolonged bone masses. MATERIALS AND METHODS: We studied 20 bone masses that showed high signal intensity on T2-weighted images and poor enhancement on contrast-enhanced T1-weighted images. These included eight solitary bone cysts, five fibrous dysplasias, and seven chondrosarcomas. To analyze diffusion changes we calculated the apparent diffusion coefficient (ADC) for each lesion. RESULTS: The ADC values of the two types of benign lesions and chondrosarcomas were not significantly different. However, the mean ADC value of solitary bone cysts (mean +/-SD, 2.57 +/- 0.13 x 10(-3) mm(2)/second) was significantly higher than that of fibrous dysplasias and chondrosarcomas (2.0 +/- 0.21 x 10(-3) mm(2)/second and 2.29 +/- 0.14 x 10(-3) mm(2)/second, respectively, P < 0.05). None of the lesions with ADC values lower than 2.0 x 10(-3) mm(2)/second were chondrosarcomas. CONCLUSION: Although there was some overlapping in the ADC values of chondrosarcomas, solitary bone cyst, and fibrous dysplasia, quantitative DWI may aid in the differential diagnosis of poorly contrast-enhanced and T2-prolonged bone masses.     

Diffusion-weighted MRI features of brain abscess and cystic or necrotic brain tumors: comparison with conventional MRI

BACKGROUND AND PURPOSE: The purpose of this study was to determine whether diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) can be used to distinguish brain abscesses from cystic or necrotic brain tumors, which are difficult to distinguish by conventional magnetic resonance imaging (MRI) techniques. METHODS: Eleven consecutive patients with brain abscesses [10 pyogenic and 1 toxoplasmosis (in an AIDS patient)] and 15 with cystic or necrotic brain gliomas or metastases were enrolled in this study. None of these lesions had apparent hemorrhage based on T1-weighted image (T1WI). The DWI was performed using a 1.5-T system, single-shot spin-echo echo-planar pulse sequence with b=1000 s/mm(2). The ADC was calculated using a two-point linear regression method at b=0 and b=1000 s/mm(2). The ratio (ADCR) of the lesion ADC to control region ADC was also measured. RESULTS: Increased signal was seen in all of the pyogenic abscess cavities to variable degrees on DWI. In vivo ADC maps showed restricted diffusion in the abscess cavity in all pyogenic abscesses [0.65+/-0.16 x 10(-3) (mean+/-S.D.) mm(2)/s, mean ADCR=0.63]. The case with multiple toxoplasmosis abscesses showed low signal intensity on DWI and high ADC values (mean 1.9 x 10(-3) mm(2)/s, ADCR=2.24). All cystic or necrotic tumors but one showed low signal intensity on DWI and their cystic or necrotic areas had high ADC values (2.70+/-0.31 x 10(-3) mm(2)/s, mean ADCR=3.42). One fibrillary low-grade astrocytoma had a high DWI signal intensity and a low ADC value in its central cystic area (0.44 x 10(-3) mm(2)/s, ADCR=0.49). Postcontrast T1WIs yielded a sensitivity of 60%, a specificity of 27.27%, a positive predictive value (PPV) of 52.94%, and a negative predictive value (NPV) of 33.33% in the diagnosis of necrotic tumors. DWI yielded a sensitivity of 93.33%, a specificity of 90.91%, a PPV of 93.33%, and a NPV of 90.91%. The area under receiver operating characteristic (ROC) curves for postcontrast T1WI was 0.44 and DWI was 0.92. Analysis of these areas under the ROC curves indicates significant difference between postcontrast T1WI and DWI (P<.001). CONCLUSION: With some exceptions, DWI is useful in providing a greater degree of confidence in distinguishing brain abscesses from cystic or necrotic brain tumors than conventional MRI and seems to be a valuable diagnostic tool.     

Diffusion-weighted imaging of breast cancer with the sensitivity encoding technique: analysis of the apparent diffusion coefficient value.

PURPOSE: The usefulness of diffusion-weighted imaging (DWI) in the field of neuroradiology has been established. Despite its high contrast resolution, DWI has the disadvantages of susceptibility artifact and chemical shift artifact. We performed DWI of breast cancer with the sensitivity encoding (SENSE) technique. METHODS: The subjects were 60 female patients with breast mass. All patients underwent MRI including SENSE-DWI and were diagnosed histologically. Of these patients, 55 were diagnosed with breast cancer and the remaining five were diagnosed with benign mass. The histological diagnoses of breast cancer were as follows: 39 cases of invasive ductal carcinoma (IDC); 11 cases of IDC with a predominant intraductal component and non IDC (pure or predominant NIDC); and five cases of special types of cancer. The MR system used was a Gyroscan Intera 1.5T (Philips Medical Systems). In addition to routine MRI for breast cancer, including contrast-enhanced dynamic, SENSE-DWI was obtained. The accuracy of the positional information of SENSE-DWI was visually compared with that of conventional images. The apparent diffusion coefficient (ADC) values of breast mass were analyzed with SENSE-DWI. RESULTS: The accuracy of positional information was adequate for diagnosing of all patients. The mean ADC value of breast cancer was 1.021x10(-3) mm2/s and that of benign mass was 1.488x10(-3) mm2/s (p=0.0002). The mean ADC value of IDC was 0.968x10(-3) mm2/s and that of pure or predominant NIDC was 1.218x10(-3) mm2/s (p=0.0011). CONCLUSION: SENSE-DWI was of sufficient quality to support diagnosis of breast mass. SENSE-DWI may permit the acquisition of more detailed information about lesions, including tumor cellularity, that is difficult to obtain with conventional techniques.     

Thin-section diffusion-weighted magnetic resonance imaging of the brain with parallel imaging

BACKGROUND: Thin-section diffusion-weighted imaging (DWI) is known to improve lesion detectability, with long imaging time as a drawback. Parallel imaging (PI) is a technique that takes advantage of spatial sensitivity information inherent in an array of multiple-receiver surface coils to partially replace time-consuming spatial encoding and reduce imaging time. PURPOSE: To prospectively evaluate a 3-mm-thin-section DWI technique combined with PI by means of qualitative and quantitative measurements. MATERIAL AND METHODS: 30 patients underwent conventional echo-planar (EPI) DWI (5-mm section thickness, 1-mm intersection gap) without parallel imaging, and thin-section EPI-DWI with PI (3-mm section thickness, 0-mm intersection gap) for a b value of 1000 s/mm(2), with an imaging time of 40 and 80 s, respectively. Signal-to-noise ratio (SNR), relative signal intensity (rSI), and apparent diffusion coefficient (ADC) values were measured over a lesion-free cerebral region on both series by two radiologists. A quality score was assigned for each set of images to assess the image quality. When a brain lesion was present, contrast-to-noise ratio (CNR) and corresponding ADC were also measured. Student t-tests were used for statistical analysis. RESULTS: Mean SNR values of the normal brain were 33.61+/-4.35 and 32.98+/-7.19 for conventional and thin-slice DWI (P>0.05), respectively. Relative signal intensities were significantly higher on thin-section DWI (P<0.05). Mean ADCs of the brain obtained by both techniques were comparable (P>0.05). Quality scores and overall lesion CNR were found to be higher in thin-section DWI with parallel imaging. CONCLUSION: A thin-section technique combined with PI improves rSI, CNR, and image quality without compromising SNR and ADC measurements in an acceptable imaging time.     

磁共振弥散成像在鼻咽癌颈部淋巴结转移调强放射治疗中的应用

目的 探讨磁共振弥散成像(DWI)及表观弥散系数(ADC)在鼻咽癌颈部淋巴结转移调强放射治疗(intensity modulated radiation therapy,IMRT)前的诊断及其对放化疗反应的监测能力.方法 对18例病理确诊的鼻咽癌患者在治疗前、治疗中每周及治疗后1个月行DWI检查.所有患者均接受头颈部IMRT及铂类同步化疗.在DWI上共分析了52枚颈部异常淋巴结,将其分为最短径≥10 mm(32枚)及<10 mm(20枚)两组,测量比较治疗前两组的ADC值是否存在差异,观察所有淋巴结治疗过程中ADC值的动态变化,同时观察比较治疗后残存的颈部淋巴结与正常舌肌的ADC值.结果 最短径≥10 mm淋巴结的平均ADC值为(0.71±0.12)×10-3mm/s,与最短径<10 mm者的平均ADC值[(0.73±0.16)×10-3mm/s]差异无统计学意义(t=1.11,P=0.27).治疗前52枚淋巴结的平均ADC值明显低于正常舌肌(t=19.35,P＜0.01).治疗过程中ADC值逐渐上升,以第1、2周改变最明显,以后趋于平稳.治疗后残留淋巴结的ADC值明显增大,与治疗前比较差异有统计学意义(t=12.72,P＜0.01),与正常舌肌比较差异无统计学意义(t=0.34,P=0.73).结论 在鼻咽癌IMRT中,DWI对诊断颈部转移性淋巴结以及监测后者对放化疗的反应具有重要参考价值,从而帮助临床医生合理制定并及时更改放疗计划.

Abstract：

Objective To investigate the value of diffusion-weighted magnetic resonance imaging (DWI) and apparent diffusion coefficients (ADC) in detecting metastatic lymph nodes from nasopharyngeal carcinoma (NPC),and predicting the response of these nodes to concurrent chemoradiation (CRT).Methods Eighteen patients with pathologically proven NPC received conventional magnetic resonance imaging (MRI) and DWI before treatment,weekly during treatment,and one month after treatment.DWI was performed using a single-shot echo-planar (SSEPI) MR imaging sequence with b values of 0 and 1500 s/mm2.ADC maps were reconstructed for all patients and ADC values were calculated for each lymph node and tongue muscle.Totally fifty-two morphologically abnormal lymph nodes were analyzed.The ADC values of the metastatic lymph nodes before treatment were compared between those with the short axis≥10 mm (n=32) and those with the short axis<10 mm (n=20),and the dynamic changes in ADC values of the lymph nodes before,during,and after therapy were observed and recorded.Results The average ADC of the 32 lymph nodes with the short axis ≥ 10 mm was (0.71±0.12) x 10-3mm/s,not significantly different from that of the 20 lymph nodes with the short axis < 10 mm [(0.73±0.16) x 10-3mm/s,t = 1.11 ,P =0.27].The average ADC values of these lymph nodes before treatment was significantly lower than that of the tongue muscle (t = 19.35,P < 0.0001).During CRT,the ADC values of the lymph nodes increased gradually,with the most evident change in the first two weeks before reaching a relatively flat plateau thereafter.The ADC value of the residual lymph nodes after CRT was significantly higher than that before treatment (t = 12.72,P < 0.0001),however,not statistically significant different from that of the normal tongue muscle (t = 0.34,P = 0.73).Conclusions DWI plays an important role in diagnosing the metastatic lymph nodes from NPC and is feasible for observation of the early response of the lymph nodes to IMRT,thus helping the clinicians make appropriate treatment planning and replanning in the course of radiotherapy.     

DWI在胆囊壁增厚性病变中的诊断价值

目的 评价扩散加权成像(DWI)在胆囊壁增厚性病变中的诊断价值.方法 回顾性分析42例胆囊壁增厚性病变(16例胆囊癌和26例胆囊良性病变)的常规MRI及DWI图像,并由2位医师比较常规MRI、融合图像(DWI+T2WI)视觉评估、表观扩散系数(ADC)值的测量3种方法在判别胆囊壁增厚性病变良恶性的能力.结果 常规MRI、融合图像视觉评估、ADC值测量的受试者工作特征(ROC)曲线的曲线下面积(AUC)分别为0.570、0.849、0.901.常规MRI方法诊断的准确度、敏感性和特异性为59.5%、62.5%、57.7%;融合图像视觉评估的方法诊断的准确度、敏感性和特异性为85.7%、81.2%、88.5%;ADC值测量的准确度、敏感性和特异性为83.3%、80.0%、85.2%.胆囊癌组的平均ADC值[(1.15±0.35)×10-3mm2/s]明显低于胆囊良性病变组[(1.99±0.61)×10-3mm2/s](P<0.01).结论 DWI(融合图像的视觉评估和ADC值的测量)在胆囊壁增厚性病变良恶性质的判定中具有非常重要的价值.