Finding circles in a thresholded image

I am trying to find the center, radius and area of a circle. The circles edge is a gradient from black to white so I am trying to threshold it so I can manipulate where the circles edge starts.

The image is:

My current code is:

clear all
clc

T1 = imread('T2.png');
figure(1) 
imshow(T1)

% Threshold to find circles
BI = T1 < 10;
% Removes elements less than 10 pixels
BI = bwareaopen(BI, 10);
figure(2)
imshow(BI)

[centers, radii, metric] = imfindcircles(BI,[10 200]);%Finds circles between a b pixels 
viscircles(centers, radii,'EdgeColor','b');%Draws on edge

Ar = radii'*3.14;%Finds area 

%Outputs center, radius and Area
centers
radii
Ar

Answer 1

[Harrison Law]

This is what I ended up doing:

clear all, clc

T2 = imread('T2.png');

%Threshold image
BW = T2 > 100;%Lower number = more white
BW2 = BW;
ext = logical(ones(numel(BW(:,1)),1));
BW2 = [ext BW2 ext];
BW2 = imdilate(BW2,ones(3));
BW2 = imfill(BW2,'holes');
BW2 = imerode(BW2,ones(3));
BWout = BW2(:,2:end-1);

imshow(T2)
[centers, radii, metric] = imfindcircles(BWout,[10 200]);%Finds circles between a b pixels 
viscircles(centers, radii,'EdgeColor','b');%Draws on edge

Ar = radii'*3.14;%Finds area 

%Outputs center, radius and Area
centers
radii
Ar

Answer 2

[KSSV]

USe this: https://in.mathworks.com/matlabcentral/fileexchange/9168-detect-circles-with-various-radii-in-grayscale-image-via-hough-transform?focused=5171151&tab=function