regex select multilines in powershell

I created a file like this

echo "test 1", Hello, foo, bar, world, "test 2" > test.txt

and the result is this:

test 1
Hello
foo
bar
a better world
test 2

I need to remove all the text starting with the keyword "Hello" and ending with "world", including both keywords.

Something like this

test 1
test 2

I tried

$pattern='(?s)(?<=/Hello/\r?\n).*?(?=world)'
(Get-Content -Path .\test.txt -Raw) -replace $pattern, "" | Set-Content -Path .\test.txt

but nothing happend.
What can I try?

>Solution :

Assuming you want to remove the starting and ending keywords you could use either (?s)\s*Hello.*world or (?s)\s*Hello.*?world depending on if you want .* to be greedy or lazy.

(Get-Content path\to\file.txt -Raw) -replace '(?s)\s*Hello.*world' |
    Set-Content path\to\result.txt

Use -creplace for case sensitive matching of the keywords.