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Knee Protocol

Overview

         Evaluation of the knee including the patello-femoral joint, medial and lateral compartments as well as related tendons and ligaments and the popliteal fussa is performed with a high resolution proton density sequence acquired in 3 planes: Axial, Sagittal and Coronal. Start with the axial sequence and then use this as a locator for prescribing the subsequent sequences. Evaluation of bone marrow for contusion requires a STIR or T2 fat saturation sequence in either coronal or sagittal planes. If the patient has a suspicious mass then post-Gd T1 fat saturation images are help to determine if the mass is benign or malignant and better delineate its full extent. An arteriogram can be obtained during the injection of the gadolinium. Finally in patients with hemophilia or PVNS a gradient echo sequence is useful for evaluating the extent of hemorrhagic synovitis.

	Axial PD	Sag PD	Coronal PD	Coronal T2 FatSat	Cartilage (Optional)
IMAGING PARAMETERS
Plane	Axial	Oblique	Oblique	Oblique	Sagittal
Mode	2D	2D	2D	2D	3D
Pulse Seq	FSE	FSE	FSE	FSE	SPGR
Imaging Options	NPW	FC,NPW	NPW, FC,	NPW, FC,
SCAN TIMING
# of Echoes	1   ETL10	1   ETL=6	1   ETL=10	1   ETL=8	1
TE	34	34	34	68	6
TR	4100	4000	4200	3200	39
Flip Angle	-	-	-	-	40 degrees
Bandwidth	32	32	16	16	15.6
ADDITIONAL PARAMETERS (see attached instructions)
SAT	S,I	S,I	S,I	Fat, S,I	Fat
ACQUISITION TIMING
Freq	512	512	512	256	256
Phase	256	256	256	256	160
NEX	2	2	2	2	0.75
Phase FOV	1	1	-	-	1
Locs Before Pause	-	-	0	0
Freq DIR	A/P	A/P	R/L	R/L	S/I
Auto Center Freq	Peak	Water	Water	Water	Water
Auto Shim	On	Off	Off	On	On
Contrast	-	-	-	-
SCANNING RANGE
FOV	18 (12-20)	16 (12-20)	18 (10-18)	18 (10-20)	14 (10-20)
Slice Thickness	4	3	3.6	3.6	1.5 (1-2)
Spacing	0.4	0	0.4	0.4
Start - End	S55-I46
# Slices	24	31	20	20	60 (40-80)
Scan Time	4 min.	6:00 min.	4:46 min.	3:24 min.	5:03 min.

Scheduling Guidelines:

• First Ask
• Is there a mass?______ When did you first discover the mass?_______________________

• Does the problem relate to a recent injury?  YES   NO    DATE_____________________
• Where does the knee hurt (  FRONT  -  BACK  -  INSIDE  -  OUTSIDE  )?
• Have you had surgery on your knee?   YES   NO    DATE__________________________
• Have you had an x-ray?  
• If “mass” then schedule in early morning with Radiologist monitoring. Patient may need gadolinium
• Otherwise schedule anytime.
• Instruct patient to bring x-rays if available.

 

Patient Preparation:

·       Fill out safety screening and clinical information form

·       Vitamin E capsule on the site of symptoms and on any masses

·       Measure distance left or right from centerline of magnet

 

Coil: Extremity. Slightly externally rotate the foot by about 10-15 degrees to stretch the anterior cruciate ligament.

Pack some cushions around the knee to help it stay motion-free. A small cushion under the ankle helps to keep the leg straight.

 

Landmark: inferior region of patella.

 

Patient Positioning:  Supine, feet first.

 

Series 1:  Axial Proton Density

Enter left or right offset corresponding to distance from centerline of magnet. Then SCAN.

Right knee:	offset	R 75
Left knee:	offset	L 75

 

                                                                                     

Series 2:  Sagittal Proton Density

• Oblique to the intercondylar notch
• Include all of medial and lateral menisci. Subcutaneous fat medial and lateral to knee joint may be excluded. If more slices are required, increase TR.

 

Series 3:  Coronal Proton Density

• Oblique perpendicular to series 2.
• If more slices are required, increase TR.
• Keep TR > 3000 and ETL < 16
• If there is bone abnormality or soft tissue mass then it may be necessary to increase FOV.

 

Series 4:  Coronal T2 Fat Sat  (same as series 3 above)

 

 

Series 5:  Optional Cartilage:

• Usually cartilage is well seen on the proton density sequences (series 1-3). However this in patients with cartilaginous injuries, this extra sequence optimized for cartilage may be useful.
• Do not film this sequence. It is viewed on the computer work station.

 

If there is a Solid Mass suspicious for CANCER:

then make sure there is a vitamin E capsule marking the site of the mass and perform dynamic 2D or 3D Gd MRA during the injection of single dose gadolinium followed by axial and either sagittal or coronal T1 fat sat spin echo sequences

 

Series 6:  Optional 2D Projection MRA

• This requires a custom pulse sequence written by Yi Wang. Actually 2 programs are required, one for data acquisition and another for data processing to perform complex subtractions.(yiwang@mail.med.cornell.edu)
• Set slab width to include mass and arteries: typically 50-100 mm.
• Sagittal: if mass is on front or back of knee
• Coronal if mass is on medial or lateral aspect of knee
• Select enough phases to last for 60 seconds
• Recontruction Instructions:
• Open C-shell under utilities menu 
• Change directory:        cd /usr/g/mraw
• List files                      plist
• Run post-processing  lx2dsa
• Use the second image as a mask for subtraction and store as series 20.  
• repeat the subtraction using a mask which immediately precedes arrival of contrast in popliteal artery

 

Series 7:  Optional Post Gd T1 fat sat 

• Perform in axial plane as 4-10 mm thick slices covering the mass with interleave or 25% gap
• Keep the TR under 600msec
• TE min full : do not use minimum TE
• Obtain one additional plane:
• Sagittal if the mass is on the front or the back
• Coronal if the mass is on the left or the right side

 

If there is hemophilia or if PVNS is suspected:

Do a gradient echo sequence

Series 8:  Optional Gradient Echo:

• This sequence is useful for patient with hemophilia or PVNS
• Make sure to cover all of the synovium

 

Series 9:  Optional Sagittal Spin Echo Proton Density:

This sequence is for use when fast spin echo is not considered adequate to diagnose a meniscal tear. It replaces series 2. Note that there is controversy over whether spin echo or fast spin echo is superior for diagnosing meniscal tears.

 

Filming Instructions:

Series 1           2 sheets 12 on 1           zoom in and shift to center knee

Series 2           2 sheets 12 on 1           and also film meniscal windows

Series 3           2 sheets 12 on 1

Series 4           2 sheets 12 on 1

 

ICD9 Codes

Internal derangement of knee	717.0-717.9
Articular cartilage disorder, site unspecified	718.00
Tear of medial cartilage or meniscus	836.0
Tear of lateral cartilage or meniscus	836.1
Other tear of cartilage or meniscus	836.2
Sprains and strains of knee and leg	844.0-844.9
Ankylosis of joint, fibrous, osseous	718.05
Cyst of bone	733.20-733.29
Malignant neoplasm lower limb	195.5
Benign neoplasm, short bones of lower limb	213.8
Lesion of lateral popliteal nerve	355.3
Lesion of medial popliteal nerve	355.4
Aneurysm of lower extremity	442.3

 

Billing code:

(any joint, lower extremity)                 73721

 

Sample Dictation

Dr.

 

Re:              

Exam:                   knee MRI

Exam Date:          January , 2000

 

Clinical Statement:  knee pain

 

Technique:              Extremity coil (right knee only):

Axial, Sagittal and Coronal  proton density

Coronal T2 with fat saturation

Sagittal 3D SPGR fat sat for cartilage

                   

 

Findings:       

Effusion:                                                                  

Patella retinaculae:                      

Anterior cruciate ligament:                

Posterior cruciate ligament:      

Popliteus tendon:                            

Lateral collateral lig complex:      

Medial collateral ligament::               

Medial meniscus:                         

Lateral meniscus         

Bone marrow:                           

Cartilage:                                   

Patella tendon:                            

Quadracepts tendon                   

 

 

 

Impression:

 

 

Examples: