Diffusion-weighted MRI compared to FDG PET/CT for assessment of early treatment response in lymphoma

Abstract

Background

18F fluoro-deoxyglucose (FDG) positron emission tomography / computed tomography (PET/CT) is a well-recognized diagnostic tool used for staging and monitoring of therapy response for lymphomas. During the past decade diffusion-weighted (DW) magnetic resonance imaging (MRI) is increasingly being included in the assessment of tumor response for various cancers.

Purpose

To compare the change in maximum standardized uptake value (ΔSUVmax) from FDG PET/CT with the change in apparent diffusion coefficient (ΔADC) from DW MRI after initiation of the first cycle of chemotherapy in patients with Hodgkin's lymphoma (HL) and in patients with diffuse large B-cell lymphoma (DLBCL).

Material and Methods

Twenty-seven consecutive patients with histologically proven lymphoma and lymphomatous lymph nodes (LLN) of the neck (19 with HL, 8 with DLBCL) underwent FDG PET/CT and MRI of the neck before and after initiation of the first cycle of chemotherapy. The mean time interval from initiation of chemotherapy to imaging was 19 days and 2 days for FDG PET/CT and MRI, respectively. For each patient ΔSUVmax, ΔADC, and change in volume of the same LLN were compared.

Results

There was a significant mean decrease of SUVmax by 70%, but no significant change in ADC. There was no significant reduction in LLN volume.

Conclusion

There was no significant correlation between ΔSUVmax and ΔADC. Thus, our data do not support that FDG PET/CT can be replaced by early DW MRI for response evaluation in lymphoma patients.

Keywords

FDG PET/CT DW MRI lymph nodes lymphoma neck

Introduction

As lymphoma patients often are treated with curable intent (1 –3), accurate response evaluation for early response-adapted therapy is important, avoiding ineffective treatment and unnecessary side-effects.

During the past decade 18F fluoro-deoxyglucose (FDG) positron emission tomography / computed tomography (PET/CT) has increasingly been included in primary staging, functional assessment of disease behavior, metabolic response to treatment, and detection of recurrence for lymphoma patients (4 –6). Interim FDG PET/CT evaluation performed after a few cycles of chemotherapy has shown to have prognostic value for treatment outcome and survival in patients with Hodgkin's lymphoma (HL) and in patients with diffuse large B-cell lymphoma (DLBCL) (4,7 –9). Although there are no guidelines as to when the interim examination should be performed (10,11), the current advice is to carry out interim assessment after two and/or four cycles of chemotherapy (12). It has been shown that FDG uptake in lymphoma decreases as early as 1 day after the initiation of chemotherapy (13). Maximum standardized uptake value (SUVmax) is the most common quantitative measure in PET/CT analyses in oncology (14), and percent change in SUVmax (ΔSUVmax) is often used for interim evaluation (15,16). A recent study concluded that interim assessment with FDG-PET/CT has a high negative predictive value (NPV), but low positive predictive value (PPV) in patients with advanced-stage DLBCL (17). In HL, interim FDG PET/CT is used in several prospective clinical studies and may lead to a paradigm shift in the treatment of this disease (18).

Magnetic resonance imaging (MRI) is increasingly being included in the assessment of lymphoma (19,20). Recently, diffusion-weighted (DW) MRI has successfully been applied for monitoring tumor response following different therapeutic interventions (21). The signal intensity (SI) in DW MRI reflects the restriction of water molecules to move within tissues. Malignant tumors show high SI on DW MRI because of high cellular density, limiting the freedom of water molecules to move (22). The diffusion can be quantified by calculation of the apparent diffusion coefficient (ADC) (23). DW MRI can be carried out in a few minutes, there is no need for administration of contrast medium, and the examination does not rely on the use of ionizing radiation, which could be particularly advantageous for repeated follow-up surveillance in lymphoma patients. Compared to FDG PET/CT, DW MRI is readily available, requires fewer resources, and can be performed at a lower cost (24).

The purpose of the study was to explore the association between ΔSUVmax and ΔADC after initiation of the first cycle of chemotherapy in patients with Hodgkin's lymphoma (HL) and diffuse large B-cell lymphoma (DLBCL).

Material and Methods

Study population and study design

Between February 2009 and November 2012, 33 consecutive patients (20 men, 13 women) with enlarged lymphomatous lymph nodes (LLN) of the neck referred for staging of histologically proven lymphoma were included in this prospective study. Their ages were in the range of 22–80 years (mean, 49.2 years), and their body weights were in the range of 50–112 kg (mean, 80.7 kg). The regional ethics committee approved the investigational protocol. All patients were given both oral and written information about the study and provided their written consent before inclusion. A flow-chart of the study is shown in Fig. 1. Of the 33 included patients, 23 patients were diagnosed with HL and 10 with DLBCL. All except two patients underwent baseline CT, baseline MRI of the neck, and FDG PET/CT prior to receiving the first cycle of chemotherapy. Based on the initial diagnostic CT examination, a single LLN located at level 2A (jugulodigastric) (denoted the index lesion) was chosen for exploring the potential of the ADC as an early marker of treatment response. Neck nodes on CT were considered lymphomatous if their shortest axial diameter was larger than 11 mm (25). Long-axis diameter (LAD) and short-axis diameter (SAD) in the axial plane at MRI was measured and lymph node volume was calculated using the formula for the volume of an ellipsoid (26).

Baseline FDG PET/CT was performed 1–25 days (mean, 6 days) before initiation of the first cycle of chemotherapy, interim FDG PET/CT was performed 9–30 days (mean, 19 days) after initiation of the first cycle of chemotherapy, and 0–17 days (mean, 5 days) before initiation of the second cycle of chemotherapy.

Baseline MRI was performed 0–26 days (mean, 7 days) before initiation of the first cycle of chemotherapy, interim MRI was performed 1–4 days (mean, 2 days) after initiation of the first cycle of chemotherapy, and 9–27 days (mean, 21 days) before initiation of the second cycle of chemotherapy. The mean number of days between interim DW MRI and interim FDG PET/CT was 18 days (range, 9–29 days).

Treatment procedures

Patients with HL stage I–IIA received two to four cycles of doxorubicin, bleomycin, vincristine, and dacarbazine (ABVD) followed by local radiotherapy of 20–30 Gy. ABVD was given at days 1 and 15 in 4-weekly cycles. DLBCL patients stage I–II were given four to six cycles of the anti-CD20 monoclonal rituximab (R) combined with cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) chemotherapy given with an interval of 2 weeks with granulocyte colony-stimulating factor (G-CSF) support for patients with elevated serum lactate dehydrogenase (s-LDL), otherwise every 3 weeks. Patients with stage III–IV disease were given at least six courses of R-CHOP. Radiotherapy was given in addition to chemoimmunotherapy in line with national guidelines but administered after the last FDG PET/CT and MRI examination according to the study protocol in this investigation.

Imaging

Twenty-seven patients (19 with HL) underwent interim FDG PET/CT and interim MRI after initiation of the first cycle of chemotherapy (Fig. 1). FDG PET/CT was performed using a Siemens Biograph 16 (Siemens Healthcare, Munich, Germany) PET/CT scanner. After 6 h of fasting 370 ± 37 MBq FDG was injected, and the patient was resting in a bed in a quiet, dim room for 1 h before scanning. PET data were collected from the skull base to the proximal thighs using 3 min scan time per bed position and 25% overlap between bed positions. Data acquisition and reconstruction were performed on Siemens Navigator / Wizard computers, and image evaluation and SUV measurements were performed on Siemens Leonardo / Multimodality work stations using the program True-D (Siemens Healthcare, Munich, Germany). The acquired PET data were reconstructed using three-dimensional ordered subset expectations maximization (OSEM) interactive algorithm with eight subsets and four iterations. Image pixel size was 3.5 mm displayed in a 168 × 168 matrix array. Emission data were corrected for scatter, random events, and dead-time losses, and a post-reconstruction Gaussian smoothing filter with full width half maximum of 5 mm was applied to the images. The CT images obtained from helical volume mode scanning (rotation time, 0.5 s; pitch, 0.75; peak tube voltage, 120 kV; quality reference mAs, 50 for integral automatic exposure control [CareDose]; slice thickness, 5 mm; distance between slices, 3 mm) were automatically fused with the PET images. The tracer uptake was quantified using the SUVmax being the decay-corrected ratio of the highest voxel activity within a selected volume to the injected dosage corrected for the body weight (27).

The patients underwent MRI using a 1.5 T Siemens Espree scanner (Siemens Healthcare, Erlangen, Germany) and a phased-array neck matrix coil. The MR protocol consisted of axial fast spin-echo T2-weighted (T2W) images (TR/TE, 3540/74 ms; slice thickness, 3 mm; slice gap, 1 mm; number of excitations [NEX], 2; voxel size, 0.9 × 0.8 × 3 mm) and axial DW MRI. The DW MR images were acquired using a presaturation inversion recovery (SPAIR) single-shot spin-echo planar imaging sequence and 4 b-values (50, 500, 1000, and 1600 s/mm²) in three orthogonal directions (TR/TE, 5000/80 ms; slice thickness, 3 mm; slice gap, 1 mm; NEX, 6; voxel size, 2.3 × 2.3 × 3 mm). The total acquisition time for the two MR sequences was 12 min. ADC maps were obtained using the online MRI scanner software.

After the initial baseline examinations two patients declined to undergo further study-specific imaging examinations. Patients were excluded due to lack of interim MRI (n = 2), suboptimal interim MR image quality (n = 1), and insufficient fasting before baseline FDG PET/CT (n = 1) (Fig. 1).

Image interpretation

The FDG PET/CT images were interpreted by two experienced nuclear medicine specialists in consensus, having 7 and 10 years of clinical PET/CT experience. The PET images and the fused PET/CT images (axial, sagittal, and coronal slices) as well as the maximum intensity projection (MIP) of the PET images were all studied. The SUVmax was obtained from a circular volume of interest (VOI) placed over the selected LLN. All PET/CT studies were compared side by side with available, relevant contrast-enhanced CT images. ΔSUVmax was calculated as the percentage change in SUVmax between baseline FDG PET/CT and interim FDG PET/CT (28).

The MR images were interpreted by a radiologist having 7 years of experience in oncological radiology. Mean ADC of individual LLN was obtained by manually delineating the LLN in the slice where the LLN had its largest extent using the AGFA medical picture archiving and communication system (Impax 5.4, AGFA, Mortsel, Belgium). The delineation of the region of interest (ROI) was guided by the T2W images to ensure the same lesions being compared between modalities. ΔADC was calculated as the percentage change in ADC between baseline DW MRI and interim DW MRI (28).

Statistical analysis

All statistical analyses were performed using Microsoft® Excel 2002 SP3 (Microsoft Cooperation, Redmond, WA, USA). Comparisons between pretreatment and interim values were assessed using the two-sided paired samples Student's t-test. The Pearson rho test was used to evaluate correlations between ΔADC and ΔSUVmax. Statistical significance was set to 5% (P ≤ 0.05) in all analyses.

Results

There was a statistically significant decrease in SUVmax from baseline FDG PET/CT (mean, 11.7; range, 3.7–28.0) to interim FDG PET/CT (mean, 3.2; range, 1.2–9.7) (P < 0.001). The mean ΔSUVmax for the 27 patients showed a decrease of 70% and for 25 out of the 27 patients the decrease in SUVmax was more than 40% (Fig. 2). There was no significant difference in ΔSUVmax between LLN with HL and LLN with DLBCL (P = 0.99).

The DW MR images were of diagnostic quality and had high contrast-to-noise ratio with the SI of the LLN being elevated compared to that of the surrounding normal tissue. MRI-assessed mean LLN volume decreased from 13.1 cm³ (range, 0.4–173.8 cm³) at baseline MRI to 6.4 cm³ (range, 0.3–68.9 cm³) at interim MRI yielding a mean volume reduction (ΔVolume) of 31%, albeit not statistical significant (P = 0.3). Before treatment the mean SAD of the LLN was 20 mm (range, 12–45 mm). There was no statistically significant difference in LAD (P = 0.3) and SAD of the lesions (P = 0.3) at interim MRI. Mean ΔADC was 5.3% (P = 0.6) with values ranging from a decrease of 0.20 × 10^–3 mm²/s to an increase of 0.28 × 10^–3 mm²/s for individual LLN. There was no difference between mean ADC at baseline (0.64 × 10^–3 mm²/s; range, 0.45 × 10^–3 – 1.10 × 10^–3 mm²/s) and at interim (0.67 × 10^–3 mm²/s; range, 0.47 × 10^–3–1.14 × 10^–3 mm²/s) for the 27 patients that underwent both MRI examinations (P = 0.6). At baseline there was no significant difference in ADC between patients with HL (0.65 × 10^–3 mm²/s) and DLBL (0.62 × 10⁻³ mm²/s) (P = 0.67). For ΔADC there was a significant difference between the two groups of patients (HL, 0.8%; DLBCL, 16.2%; P = 0.05).

There was no significant correlation between ΔSUVmax and ΔADC for the two patient groups separately (HL, ρ = 0.13; P = 0.17; DLBCL, ρ = 0.48; P = 0.08) or combined (ρ = 0.3; P = 0.1) (Fig. 2).

Discussion

In our study we found no change in ADC of the LLN after initiation of the first cycle of chemotherapy for lymphoma despite significant decrease in SUVmax indicating clinical response (Fig. 2). There was no significant LLN volume reduction.

The mean ΔSUVmax for the 27 patients included in our study showed a decrease of 70% 19 days after initiation of the first cycle of chemotherapy clearly indicating reduced metabolic activity (29). Although a recent international workshop on positron emission tomography in lymphoma suggests to use the same 5-point visual grading scale for interim and for end of treatment reporting (30), the use of percent change in SUVmax has been and is being used by several groups (15,16).

We found no change in the ADC of the selected LLN after initiation of the first cycle of chemotherapy. The ADC is a quantitative measure of the random microscopic motion of water molecules within tissue (22). Our findings may indicate that the microstructure of the LLN is similar at the two different measuring points (baseline and interim): intact cancer cells with intact diffusion barriers and elevated nuclear-to-cytoplasmatic ratio (31). A recent study reported increased ADC values during the first week of treatment (32), but most early therapeutic response evaluations of lymphoma have been performed after more than one cycle (33).

An inverse correlation between ADC and SUVmax at initial staging of lymphoma has been demonstrated (33,34) as well as after two cycles of chemotherapy (23). In our study, no such correlation was found.

FDG PET/CT has improved the interim response evaluation for HL and DLBCL (8,9), and DW MRI is claimed to complement FDG PET/CT for interim treatment response in lymphoma (23), however, the modalities have shortcomings (24,33). The integration of PET with MRI represents a promising tool which potentially opens new perspectives in clinical molecular imaging with advantages as superior soft tissue contrast and less radiation exposure (12,35).

Our study included patients with HL and DLBCL. The cellular component of HL (predominantly inflammatory cells) differs markedly from that of non-Hodgkin's lymphoma (NHL) (predominantly malignant lymphocytes) (36). Unlike other tumor types the ADC response to chemotherapy in HL may relate to changes in the population of inflammatory matrix rather than the population of tumor cells themselves (23). In this study there was no significant difference in ΔSUVmax between HL and DLBCL. However, ΔADC was significantly higher for DLBCL compared to HL, and this different response to treatment might be related to the different cellular components of HL and DLBCL. Further studies are needed in order to address the value of DW MRI for response monitoring in different subclasses of lymphoma.

Our study has limitations. First, the study population is relatively small, but it consists of a homogenous population of HL and DLBCL patients who received standard immunochemotherapy and had consistent timing and interpretation of the FDG PET/CT and the DW MRI. The selection of individual LLN in a limited anatomic area of the neck was based on CT criteria and not on baseline FDG-uptake or the results at baseline DW MRI. Although other local or regional lymph nodes showed higher baseline FDG-uptake or lower ADC values at baseline DW MRI, the calculated values of all selected nodes strongly suggested active disease compatible with the diagnosis of lymphoma (Fig. 3). Second, the time point for assessment of changes in SUVmax and ADC was different. We did not acquire interim DW MRI data at the same time as interim FDG PET/CT. In order to be able to reliably differentiate between therapeutic tumor response and post-therapeutic changes, such as edema and inflammation, the median interval between the completion of chemotherapy and interim FDG PET/CT was chosen to be more than 2 weeks (18). At the time this study was designed, studies had recently shown increased ADC already a few days after onset of treatment for lymphoma (37) and significantly increased ADC values as early as 1 week after chemotherapy for lymphoma (38). Based on this knowledge and institutional logistics it was decided to perform interim DW MRI in the current study 2 days after initiation of the first cycle of chemotherapy. Interim FDG PET/CT and interim DW MRI were performed 19 days after and 2 days (all mean values) after initiation of the first cycle of chemotherapy, respectively. One might speculate that if the time interval between the interim examinations had been less, a correlation between ΔSUVmax and ΔADC might have been shown.

In conclusion, this study showed that there was no significant change in ADC of the LLN after initiation of the first cycle of chemotherapy, whereas SUVmax of the same lesion was significantly reduced, clearly indicating therapeutic response. Further prospective studies with sequential MR examinations are needed to evaluate the potential of DW MRI in predicting response to therapy.

Footnotes

Acknowledgements

We would like to thank the radiographers at Department of Radiology and Nuclear Medicine for technical assistance.

Funding

This study received financial support from Haakon and Sigrun Ødegaard Foundation and from The Norwegian Radium Hospital Research Foundation.

References

Gisselbrecht

Schmitz

Mounier

. Rituximab maintenance therapy after autologous stem-cell transplantation in patients with relapsed CD20⁺ diffuse large B-cell lymphoma: final analysis of the collaborative trial in relapsed aggressive lymphoma. J Clin Oncol 2012; 30: 4462–4469.

Fisher

. Advanced insights into the biology of malignant lymphomas. J Clin Oncol 2011; 29: 1799–1800.

Cheson

. Hodgkin lymphoma: protecting the victims of our success. J Clin Oncol 2012; 30: 4456–4457.

Hutchings

. How does PET/CT help in selecting therapy for patients with Hodgkin lymphoma? Hematology 2012; 2012: 322–327.

Afshar-Oromieh

Kratochwil

Haberkorn

. Importance of PET/CT in lymphoma diagnostics. Radiologe 2012; 52: 338–346.

de Geus-Oei

Vriens

Arens

. FDG-PET/CT based response-adapted treatment. Cancer Imaging 2012; 12: 324–335.

Hutchings

Barrington

. PET/CT for therapy response assessment in lymphoma. J Nucl Med 2009; 50: 21–30.

Yang

Ahn

Byun

. Interim PET/CT based prognostic model for the treatment of diffuse large B cell lymphoma in the post-rituximab era. Ann Hematol 2013; 92: 471–479.

Bakhshi

Radhakrishnan

Sharma

. Pediatric nonlymphoblastic non-Hodgkin lymphoma: baseline, interim, and posttreatment PET/CT versus contrast-enhanced CT for evaluation - a prospective study. Radiology 2012; 262: 956–968.

10.

Shankar

Hoffman

Bacharach

. Consensus recommendations for the use of 18F-FDG PET as an indicator of therapeutic response in patients in National Cancer Institute trials. J Nucl Med 2006; 47: 1059–1066.

11.

Bodet-Milin

Euqène

Gastinne

. The role of FDG-PET scanning in assessing lymphoma in 2012. Diagn Interv Imaging 2013; 94: 158–168.

12.

Buchbender

Heusner

Lauenstein

. Oncologic PET/MRI, Part 2: Bone tumors soft-tissue tumors, melanoma, and lymphoma. J Nucl Med 2012; 53: 1244–1252.

13.

Yamane

Daimaru

Ito

. Decreased ¹⁸F-FDG uptake 1 day after initiation of chemotherapy for malignant lymphomas. J Nucl Med 2004; 45: 1838–1842.

14.

Fuertes

Setoain

Lopez-Guillermo

. Interim FDG PET/CT as a prognostic factor in diffuse large B-cell lymphoma. Eur J Nucl Med Mol Imaging 2013; 40: 496–504.

15.

Vanderhoek

Perlman

Jeraj

. Impact of different standardized uptake value measures on PET-based quantification of treatment response. J Nucl Med 2013; 54: 1188–1194.

16.

Itti

Meignan

Berriolo-Riedinger

. An international confirmatory study of the prognostic value of early PET/CT in diffuse large B-cell lymphoma: comparison between Deauville criteria and ΔSUVmax. Eur J Nucl Med Mol Imaging 2013; 40: 1312–1320.

17.

Cashen

Dehdashti

Luo

. ¹⁸F-FDG PET/CT for early response assessment in diffuse large B-cell lymphoma: poor predictive value of international harmonization project interpretation. J Nucl Med 2011; 52: 386–392.

18.

Kostakoglu

Gallamini

. Interim ¹⁸F-FDG PET in Hodgkin lymphoma: would PET-adapted clinical trials lead to a paradigm shift?. J Nucl Med 2013; 54: 1082–1093.

19.

Thoeny

Keyzer

King

. Diffusion-weighted MR imaging in the head and neck. Radiology 2012; 263: 19–32.

20.

Vermoolen

Kersten

Fijnheer

. Magnetic resonance imaging of malignant lymphoma. Expert Rev Hematol 2011; 4: 161–171.

21.

Padhani

Koh

. Diffusion MR imaging for monitoring of treatment respons. Magn Reson Imaging Clin N Am 2011; 19: 181–209.

22.

Koh

Collins

. Diffusion-weighted MRI in the body: applications and challenges in oncology. Am J Roentgenol 2007; 188: 1622–1635.

23.

Punwani

Taylor

Ziauddin

. Diffusion-weighted MRI of lymphoma: prognostic utility and implications for PET/MRI. Eur J Nucl Med Mol Imaging 2013; 40: 373–385.

24.

Revheim

Hole

Bruland

ØS

. Multimodal functional imaging for early assessment in GIST patients treated with imatinib. Acta Oncol 2014; 53: 143–148.

25.

Som

Curtin

. Head and neck imaging 2003; Vol. 1867, 4th ed. St Louis, MO: Mosby, pp. 1910–1911.

26.

Torabi

Aquino

Harisinghani

. Current concepts in lymph node imaging. J Nucl Med 2004; 45: 1509–1918.

27.

Lin

Itti

Haioun

. Early ¹⁸F-FDG PET for prediction of prognosis in patients with diffuse large B-cell lymphoma: SUV-based assessment versus visual analysis. J Nucl Med 2007; 48: 1626–1632.

28.

Byun

Kong

Lim

. Combination of ¹⁸F-FDG PET/CT and diffusion-weighted MR imaging as a predictor of histologic response to neoadjuvant chemotherapy: preliminary results in osteosarcoma. J Nucl Med 2013; 54: 1053–1059.

29.

Kluge

Kurch

Montravers

. FDG PET/CT in children and adolescents with lymphoma. Pediatr Radiol 2013; 43: 406–417.

30.

Meignan

Barrington

Itti

. Report on the 4th International Workshop on Positron Emission Tomography in Lymphoma held in Menton, France, 3--5 October 2012. Leuk Lymphoma 2014; 55: 33–37.

31.

Velasco

Burg

Delwail

. Comparison of PET-CT and magnetic resonance diffusion imaging with body suppression (DWIBS) for initial staging of malignant lymphomas. Eur J Radiol 2013; 82: 2011–2017.

32.

Chen

Zhong

. The clinical application of whole-body diffusion-weighted imaging in the early assessment of chemotherapeutic effects in lymphoma: the initial experience. Magn Reson Imaging 2012; 30: 165–170.

33.

Kellokumpu-Lehtinen

Pertovaara

. Diffusion-weighted MRI in early chemotherapy response evaluation of patients with diffuse large B-cell lymphoma – a pilot study: comparison with 2-deoxy-2-fluoro- D-glucose-positron emission tomography/computed tomography. NMR Biomed 2011; 24: 1181–1190.

34.

Punwani

Prakash

Bainbridge

. Quantitative diffusion weighted MRI: A functional biomarker of nodal disease in Hodgkin lymphoma?. Cancer Biomarkers 2010; 7: 249–259.

35.

Appenzeller

Mader

Huellner

. PET/CT versus body coil PET/MRI:how long can you go?. Insights Imaging 2013; 4: 481–490.

36.

Hagtvedt

Aaløkken

Smith

. Enhancement characteristics of lymphomatous lymph nodes of the neck. Acta Radiol 2010; 5: 555–562.

37.

Huang

Pickup

Nelson

. Monitoring response to chemotherapy of non-Hodgkin's lymphoma xenografts by T(2)-weighted and diffusion-weighted MRI. NMR Biomed 2008; 21: 2021–2029.

38.

Nerisho

Dastidar

. Comparison of different MRI sequences in lesion detection and early response evaluation of diffuse large B-cell lymphoma – a whole-body MRI and diffusion-weighted imaging study. NMR Biomed 2013; 9: 1186–1194.